Technical Note – TN 018: 2019

For queries regarding this document

standards@transport.nsw.gov.au
www.transport.nsw.gov.au

Technical Note – TN 018: 2019

Issue date: 18 December 2019
Effective date: 18 December 2019

Subject: Publication of track drainage standard

T HR CI 12130 ST version 2.0
This technical note is issued by the Asset Standards Authority (ASA) as an update to
T HR CI 12130 MA Track Drainage, (manual) version 1.0.

ASA recently published T HR CI 12130 ST Track Drainage, (standard) version 2.0. As a result,
the cross-referencing to the standard and some content in the manual is now superseded.

Manual T HR CI 12130 MA version 1.0, Section 2.2, notes that the shaded sections are extracts
from the standard. Due to the associated standard being revised, the content of all shaded
sections (in between the horizontal bars) in this manual shall be ignored and the replacement
content shall be obtained from the current track drainage standard.

Furthermore, as noted in Section 2.2 of the standard (T HR CI 12130 ST version 2.0), where a
conflict in requirements exists between the standard and any other referenced standard or
document, which includes the manual (T HR CI 12130 MA), the standard takes precedence.

Manual T HR CI 12130 MA version 1.0, Section 9.2, provides guidance only for 'External party
development discharging onto or through the rail corridor'. External development requirements
are in T HR CI 12080 ST External Developments.

Authorisation:
Technical content Checked and Interdisciplinary Authorised for
prepared by approved by coordination release
checked by
Signature

Date
Name Malcolm Peake Richard Hitch Peter McGregor Andrea Parker
Position Senior Engineer Lead Civil Engineer A/Chief Engineer A/Executive Director
Structures

© State of NSW through Transport for NSW 2019 Page 1 of 1

 Technical Note - TN 042: 2017

For queries regarding this document

standards@transport.nsw.gov.au
www.asa.transport.nsw.gov.au

Technical Note - TN 042: 2017

Issued date: 17 October 2017

Effective date: 17 October 2017

Subject: Changes to durability requirements arising from

the publication of T HR CI 12002 ST Durability
Requirements for Civil Infrastructure
This technical note is issued by the Asset Standards Authority (ASA) to notify that the durability
requirements for civil infrastructure contained in the following documents have been superseded.

• ESC 310 Underbridges

• ESC 340 Tunnels

• T HR CI 12030 ST Overbridges and Footbridges

• T HR CI 12040 ST Overhead Wiring Structures and Signal Gantries

• T HR CI 12060 ST Retaining Walls

• T HR CI 12065 ST Station Platforms

• T HR CI 12070 ST Miscellaneous Structures

• T HR CI 12072 ST Track Slabs

• T HR CI 12130 MA Track Drainage

• T HR CI 12130 ST Track Drainage

Durability requirements are now contained in T HR CI 12002 ST Durability Requirements for Civil
Infrastructure.

© State of NSW through Transport for NSW 2017 Page 1 of 2

 Technical Note - TN 042: 2017

Authorisation:
Technical content Checked and Interdisciplinary Authorised for
prepared by approved by coordination release
checked by
Signature

Date
Name Richard Hitch Richard Hitch Jason R Gordon Jagath Peiris
Position Lead Civil Engineer Lead Civil Engineer Chief Engineer Director
Network Standards
and Services

© State of NSW through Transport for NSW 2017 Page 2 of 2

 T HR CI 12130 MA

Manual

Track Drainage

Version 1.0
Issued date: 04 September 2015

Important Warning

This document is one of a set of standards developed solely and specifically for use on Transport Assets (as defined in the Asset
Standards Authority Charter). It is not suitable for any other purpose.

You must not use or adapt it or rely upon it in any way unless you are authorised in writing to do so by a relevant NSW Government
agency. If this document forms part of a contract with, or is a condition of approval by a NSW Government agency, use of the document
is subject to the terms of the contract or approval.

This document is uncontrolled when printed or downloaded. Users should exercise their own skill and care in the use of the document.

This document may not be current. Current standards may be accessed from the Asset Standards Authority website at
www.asa.transport.nsw.gov.au.

© State of NSW through Transport for NSW

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Standard governance
Owner: Lead Civil Engineer, Asset Standards Authority
Authoriser: Chief Engineer Rail, Asset Standards Authority
Approver: Executive Director, Asset Standards Authority on behalf of the ASA Configuration Control
Board

Document history
Version Summary of Changes
1.0 First issue

For queries regarding this document,

please email the ASA at
standards@transport.nsw.gov.au
or visit www.asa.transport.nsw.gov.au

© State of NSW through Transport for NSW

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Preface
The Asset Standards Authority (ASA) is an independent unit within Transport for NSW (TfNSW)
and is the network design and standards authority for defined NSW transport assets.

The ASA is responsible for developing engineering governance frameworks to support industry
delivery in the assurance of design, safety, integrity, construction, and commissioning of
transport assets for the whole asset life cycle. In order to achieve this, the ASA effectively
discharges obligations as the authority for various technical, process, and planning matters
across the asset life cycle.

The ASA collaborates with industry using stakeholder engagement activities to assist in
achieving its mission. These activities help align the ASA to broader government expectations
of making it clearer, simpler, and more attractive to do business within the NSW transport
industry, allowing the supply chain to deliver safe, efficient, and competent transport services.

The ASA develops, maintains, controls, and publishes a suite of standards and other
documentation for transport assets of TfNSW. Further, the ASA ensures that these standards
are performance-based to create opportunities for innovation and improve access to a broader
competitive supply chain.

This document expands upon content in the ASA standard T HR CI 12130 ST Track Drainage.

This document supersedes RailCorp standard TMC 421 Track Drainage, Version 1.2. The
changes to previous content include the following:

• replacement of RailCorp organisation roles and processes with those applicable to the
current ASA organisational context

• minor amendments and clarification to content

• conversion of the standard to ASA format and style

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Foreword
This manual is intended to be used by competent personnel engaged in the provision of
services relating to rail infrastructure. Compliance with the advice in this manual will not, by
itself, be sufficient to ensure that satisfactory outcomes will be produced. Personnel providing
services based on the manual need to bring appropriate expertise to the matters under
consideration.

If, when using the manual, it is considered that the intent of stated advice is not clear, a
clarification should be sought from the ASA.

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Table of contents
1. Introduction .............................................................................................................................................. 7
2. Purpose .................................................................................................................................................... 7
2.1. Scope ..................................................................................................................................................... 7
2.2. Application ............................................................................................................................................. 7
3. Reference documents ............................................................................................................................. 7
4. Terms and definitions ............................................................................................................................. 8
5. Types of track drainage ........................................................................................................................ 10
5.1. Surface drainage ................................................................................................................................. 10
5.2. Subsurface drainage ............................................................................................................................ 12
6. Design of track drainage ....................................................................................................................... 24
6.1. Design criteria ...................................................................................................................................... 25
6.2. Design investigation ............................................................................................................................. 34
6.3. Estimation of the required drainage system capacity .......................................................................... 35
6.4. Surface drain design ............................................................................................................................ 38
6.5. Subsurface drain design ...................................................................................................................... 46
6.6. Other design considerations ................................................................................................................ 51
7. Construction of track drainage ............................................................................................................ 52
7.1. Line and grade ..................................................................................................................................... 52
7.2. Site preparation ................................................................................................................................... 53
7.3. Excavation ........................................................................................................................................... 54
7.4. Surface drain construction ................................................................................................................... 54
7.5. Subsurface drain construction ............................................................................................................. 56
7.6. Other types of construction .................................................................................................................. 61
7.7. Inlets and outlets .................................................................................................................................. 62
8. Maintenance of track drainage ............................................................................................................. 62
8.1. General ................................................................................................................................................ 62
8.2. Surface drainage ................................................................................................................................. 65
8.3. Subsurface drainage ............................................................................................................................ 66
8.4. Typical problems and solutions ........................................................................................................... 68
8.5. Preparation for flooding ....................................................................................................................... 75
9. Documentation guide ............................................................................................................................ 76
9.1. Drawing guide ...................................................................................................................................... 77
9.2. External party development discharging onto or through the rail corridor ........................................... 81
Appendix A Flow charts ......................................................................................................................... 83
A.1. Flow chart 1 – overall design process ................................................................................................. 83
A.2. Flow chart 2 – surface drainage design ............................................................................................... 84
A.3. Flow chart 3 – subsurface drainage design ......................................................................................... 85
Appendix B Drainage design checklist ................................................................................................ 86
Appendix C Design investigation form ................................................................................................. 94

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Appendix D Calculation of capacity required form ............................................................................. 96

Appendix E Drawings: typical examples.............................................................................................. 99
Appendix F R loading configuration ...................................................................................................... 100
Appendix G Further reading ................................................................................................................ 101

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1. Introduction
This manual specifies the design, construction, and maintenance guides for track drainage
systems. It covers drainage of the track formation, supporting embankments, and cuttings.

The potential effects of any drainage work need to be considered and mitigated to ensure safety
so far as is reasonably practicable in accordance with the requirements of T HR CI 12130 ST
Track Drainage.

2. Purpose
The purpose of this manual is to provide a comprehensive guide for the design, construction,
and maintenance of effective track drainage.

Regular examination, inspection, and routine maintenance of drainage systems are essential in
maintaining the integrity of the track formation, supporting embankments, and cuttings.

Neglect of drainage problems will inevitably lead to track problems.

Inspection of track drainage is included in track engineering manual TMC 203 Track Inspection.

2.1. Scope
This document covers drainage of the track formation, supporting embankments and cuttings.

This standard does not cover drainage from platforms, buildings, overbridges, footbridges,
airspace developments, external developments, access roads, roads outside the rail corridor,
council drains, or properties adjacent to the rail corridor.

This standard does not include culvert design or selection.

2.2. Application
The guidance given in this document applies to Authorised Engineering Organisations (AEOs)
that are involved in track drainage works across the full life cycle. This includes activities such
as design, construction, maintenance, and decommissioning works, which take place within the
TfNSW heavy rail corridor.

The shaded sections in this manual are extracts from ASA standard T HR CI 12130 ST Track
Drainage. Horizontal bars are also shown at the beginning and end of these requirements.

3. Reference documents
The following documents are cited in the text. For dated references, only the cited edition
applies. For undated references, the latest edition of the referenced document applies.

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Australian standards

AS 1289 Methods of testing soils for engineering purposes

AS 3706 Geotextiles – Methods of test

AS/NZS 3725 Design for installation of buried concrete pipes

AS 3996 Access covers and grates

AS 5100 Bridge design

Transport for NSW standards

ESC 310 Underbridges

ESC 410 Earthworks and Formation

ESC 540 Service Installations within the Rail Corridor

TMC 421 Track Drainage Manual

TMD 0001 CAD and Drafting Manual - All Design Areas – Sections 1 and 2

TMD 0001 CAD and Drafting Manual – Civil Design - Section 3

TMD 0001 CAD and Drafting Manual – Track Design - Section 7

TS 10765 Concessions to ASA Requirements

Transport for NSW drawings

CV 0205421 Track Drainage - Typical Sections and Notes

CV 0400998 Ballast Cage (Lobster Pot) with Removable Lid

CV 0497068 Pipe Culverts Headwalls to Suit Pipes 225-600 mm Diameter

CV 0497069 Pipe Culverts Headwalls to Suit Pipes 675-1800 mm Diameter

Other reference documents

Institution of Engineers Australia 1997, Australian Rainfall and Runoff

4. Terms and definitions

The following terms and definitions apply in this document:

AEO Authorised Engineering Organisation; a legal entity (which may include a Transport
Agency as applicable) to whom the ASA has issued an ASA Authorisation.

AR&R Australian Rainfall and Runoff (see Section 3. Reference documents)

ARI average recurrence interval

ASA Asset Standards Authority

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ASA Authorisation an authorisation issued by the ASA to a legal entity (which may include a
Transport Agency as applicable) which verifies that it has the relevant systems in place to carry
out the class of asset life cycle work specified in the authorisation, subject to any conditions of
the authorisation. The issue of ASA Authorisation confers the status of ‘Authorised Engineering
Organisation’ or AEO on the entity.

average recurrence interval the average or expected value of the periods between
exceedances of a given flood event accumulated over a given duration

catch drain intercepts overland flow or run-off before it reaches the track and related structures
such as cuttings or embankments

cess area from the edge of the ballast profile to either the edge of the embankment or the toe of
the cutting

cess drain drain located at formation level at the side of the track

Darcy-Weisbach equation an equation which relates head loss due to friction along a given
length of pipe to the average velocity of the fluid flow

DLA dynamic load allowance

down rail identified with back to Sydney as normal, the down rail will be on the left

dynamic load allowance the dynamic load allowance for railway live load effects is a
proportion of the static railway live load calculated in accordance with AS 5100

mitre drain connected to cess and catch drains to remove water or to provide an escape for
water from these drains

multiple tracks more than two tracks

OHWS overhead wiring structure

peak flow rate the highest flow discharged from the catchment under consideration having
evaluated storm durations with a particular average recurrence interval

railway corridor comprises the full volume, both above and below ground, between the centre-
line of opposing boundary fences. If no boundary fences are present, the extent of the rail
corridor will be taken as 15 m from the centre-line of the outermost rail.

SFAIRP so far as is reasonably practicable

6-foot area between two tracks

track drainage drainage of the track formation including diversion of water away from cuttings
and embankments

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5. Types of track drainage

Without adequate track drainage, track formation may become saturated, leading to weakening
and subsequent failure. Formation failure may be indicated by mud pumping up through the
ballast, repeated top and line problems, bog holes, or heaving of the formation.

If the permanent way or track structure is to be maintained at a suitable standard for the
passage of freight or high-speed passenger trains, adequate drainage needs to be installed in
new or upgraded track, and existing drainage needs to be maintained so that it works
effectively.

Track drainage consists of the following two types:

• surface drainage

• subsurface drainage

5.1. Surface drainage

Surface drainage removes surface run-off before it enters the track structure, and collects water
percolating out of the track structure.

Basic grading of the ground on either side of the track is a form of surface drainage, and allows
removal of water flowing out of the track structure.

Shoulder grading may be used in very flat areas where it is difficult to get sufficient fall for either
surface or subsurface drains. This type of grading is shown in Figure 1.

Figure 1 - Typical track formation

There are three main types of surface drainage. These are the following:

• cess drains

• catch drains

• mitre drains

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Figure 2 - Surface drainage types

5.1.1. Cess drains

Cess drains are surface drains located at formation level at the side of tracks, to remove water
that has percolated through the ballast and is flowing along the capping layer towards the
outside of the track formation. Cess drains are primarily intended for the protection of the
formation by keeping the formation dry.

Cess drains are most frequently found in cuttings where water running off the formation cannot
freely drain away.

Figure 3 - Cess drain - typical location

Surface drains can be constructed on flat grades, as they are easily cleared of any sediment
that may collect in them.

5.1.2. Catch drains

The purpose of catch drains (also known as top drains) is to intercept overland flow or run-off
before it reaches the track. They reduce the possibility of overland flow or run-off causing
damage to the track or related structures, such as cuttings or embankments.

Catch drains are generally located on the uphill side of a cutting to catch water flowing down the
hill and remove it prior to reaching the cutting.

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If this water was allowed to flow over the cutting face, it may cause excessive erosion and
subsequent silting up of cess drains.

Figure 4 - Typical catch drains

Catch drains may be used alongside tracks that cut across a slight downhill grade.

5.1.3. Mitre drains

Mitre drains are connected to cess and catch drains to provide an escape for water from these
drains. Mitre drains should be provided at regular intervals to remove water before it slows
down and starts to deposit any sediment that it may be carrying.

Figure 5 - Mitre drains

5.2. Subsurface drainage

Subsurface drainage is necessary for maintaining the integrity of the track formation and
ensuring the stability of earth slopes.

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Subsurface drainage is used for the following:

• drainage of the track structure

• controlling of ground water

• the draining of slopes

"If a drainage system is required to remove ground water and seepage, a detailed hydrological
and geotechnical investigation is required to determine the volume of water for the sizing of
drains."

The volume of water from other systems is determined from the outlet capacity of that system.

Subsurface drains are used where adequate surface drainage cannot be provided due to some
restriction or lack of available fall due to outlet restrictions. Locations where these
circumstances may occur are the following:

• platforms

• cuttings

• junctions

• multiple tracks

• bridges

"Subsurface drainage shall be provided in locations where the water table is at or near
earthworks level. Subsurface drainage shall also be provided where artesian conditions exist to
relieve water pressure.

Subsurface drainage shall be provided along the cess, between, across, or under tracks as
required."

Advice should be sought from the Principal Engineer Geotech, ASA, before designing and
installing subsurface drainage.

"Subsurface drainage systems shall be designed to transfer surface runoff, ground water and
seepage, and water collected from other drainage systems to which the new system is being
connected."

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Most systems will only have to cater for surface run-off.

5.2.1. Functions of subsurface drains

Subsurface drainage systems perform the following functions:

• collection of infiltration water that seeps into the formation (capping layer), as shown in
Figure 6

• draw-down or lowering of the watertable, as illustrated in Figure 7

• interception or cut-off of water seepage along an impervious boundary, as illustrated in

Figure 8

• drainage of local seepage such as spring inflow, as shown in Figure 9

Figure 6 - Collection of water seeping into the ballast structure

Figure 7 - Lowering the watertable

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Figure 8 - Interception and cut-off of seepage water

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Figure 9 - Drainage of local seepage

5.2.2. Types of subsurface drains

Subsurface drains normally used for track drainage can be classified into three types according
to their location and geometry as follows:

• longitudinal drain (Figure 10)

• transverse drain (Figure 11)

• drainage blankets (Figure 12)

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Figure 10 - Typical longitudinal drain arrangement

Figure 11 - Typical transverse drain

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Figure 12 - Typical drainage blanket

Two other types of subsurface drainage are the following:

• horizontal drains (Figure 13)

• vertical drains (Figure 13)

Figure 13 - Typical horizontal and vertical drain arrangement

Horizontal and vertical drains are more specialised and are seldom used for track drainage.

Horizontal drains are generally used to drain wet soils and speed consolidation of earth
structures.

Vertical drains may also be used to speed consolidation. Another type of vertical drain is used
to drain water from behind retaining walls or bridge abutments.

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5.2.3. Subsurface drain material types

Subsurface drains can also be classified according to the materials used in the drain. For
example, a subsurface drain can be classified as one of the following:

• aggregate drains

• pipe drains

• geotextile drains

• a combination of the above

Aggregate drains
These drains consist of permeable granular material. The aggregate should be coarse enough
to be free draining, but not so coarse as to allow the migration of fines into or through the
permeable material. The graded aggregate is to be wrapped in a geotextile (Figure 14).

Figure 14 - Cross-section of an aggregate drain

Pipe drains
These consist of perforated or slotted pipes, installed by trenching and backfilling. Some type of
filter material around the pipe or permeable backfill is normally required to minimise clogging of
the drain perforations or slots (see Figure 15, Figure 16, and Figure 17).

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Figure 15 - Cross-section of a typical subsoil drain used in impervious soil (for example,
clayey soils)

Figure 16 - Cross-section of a typical subsoil drain used in pervious soil (for example,
sandy soil)

Figure 17 - Cross-section of a subsoil drain where the pipe is wrapped in geotextile

(alternative slotted pipe system)

Geotextile drains
A geotextile drain may be a horizontal, vertical, or inclined blanket whose purpose is to collect
subsurface water and convey it along the plain of the fabric to an outlet. The drain needs to act
as a filter to keep soil particles out of pores and prevent clogging. An example is shown in
Figure 18.

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Figure 18 - Geotextile drain behind a retaining wall. A similar arrangement may be used
behind bridge abutments

Other types of subsurface drain

Where large volumes of water may need to be removed by subsurface drains, a carrier pipe
may be used in conjunction with a collector drain, as shown in Figure 19. With this arrangement
the collector drain does not need to carry all the water. The advantage of this arrangement is
that excess (large volumes of) water is removed from the collector drain therefore preventing it
seeping into the subgrade again at a point further down the drainage route.

Figure 19 shows a typical arrangement for a collector drain and carrier pipe located between
two tracks. The subsurface water is collected by the collector drain between the two sumps
shown. The collector drain then conveys the water to the downstream sump where it can enter
the carrier pipe and be removed without any risk of it re-entering the subgrade. See Figure 34
for an example of this system used in yard drainage.

Figure 19 - Subsoil collector drain plus a larger carrier pipe

5.2.4. Inlets and outlets

There are various types of inlets and outlets in use for subsurface drains.

The main purpose of inlet and outlet protectors is to reduce erosion. Where outlet velocities are
expected to be high, some form of energy dissipater should be installed. In addition, where the

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sediment load of the water being discharged from a drainage system is high, a silt trap should
be installed (see Figure 20 below).

Figure 20 - Typical silt trap installed in drains with high sediment loads

Some typical examples of inlet and outlet protection are the following:

• precast concrete units

• grouted sand bags (Figure 21)

• concrete (Figure 22)

• reno mattresses and gabions (Figure 23)

• revetment mattress (Figure 24)

• spalls grouted or hand packed (Figure 25)

Figure 21 - Grouted sand walls

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Figure 22 - Concrete headwall

Figure 23 - Gabion headwall

Figure 24 - Revetment mattress

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Figure 25 - Spalls used as a headwall

NOTE: As mentioned in Figure 25, on the downstream side of the outlet, water getting
under the headwall structure and causing scouring and the eventual washaway of the
headwall is a problem that cannot be overlooked. The best way to help prevent this
occurring is to provide a cut-off wall at the end of the headwall (see Figure 23 for an
example).

6. Design of track drainage

The purpose of this section is to specify design criteria and the design process to enable track
and related structures to be drained effectively using either surface or subsurface drainage
systems.

Proper drainage design, using the design process detailed in this section, may allow problems
to be discovered early and enable easier construction.

Only AEOs are allowed to design track drainage.

This section discusses the design process from the initial concept through to the detailing of the
drain capacity and components required.

Flow charts of the design process are provided in Appendix A.

A drainage design checklist is provided in Appendix B.

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"Track drainage is to be designed to capture water flows calculated in accordance with this
standard.

No other drainage shall be discharged into the track drainage system.

The design, maintenance and construction of track drainage shall only be done by an
authorised engineering organisation (AEO)."

6.1. Design criteria

Drainage systems are to be designed for the peak capacity calculated by the Rational method.
Alternatively, the Hydrograph method may be used.

"The design average recurrence interval (ARI) for track drainage (excluding siding track
drainage) shall be 50 years.

Siding track drainage shall have a design average recurrence interval (ARI) of 25 years.

The minimum design life of all track drainage components shall be 50 years.

The following configurations are not approved for track drainage on the RailCorp network:

• plastic pipes: unplasticised polyvinylchloride (UPVC); polypropylene

• inverted syphon systems.

Drainage cell systems shall only be used with the approval of the Lead Civil Engineer, ASA."

6.1.1. Surface drainage

Design criteria for surface drainage includes cess drains, catch drains, and mitre drains.

Cess drains

"The flow capacity of the open channel cess drain shall be greater than the peak flow rate.

For ease of maintenance, over-sized channels can be adopted to allow a certain degree of
sediment build up to occur and still work effectively."

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Figure 26 - Channel types

Figure 26 shows the dimensions of two channel types, trapezoidal and rectangular. If concrete
is used to form a channel then the dimension ‘B’ may be reduced to zero thereby producing a
vertical face.

"The minimum dimensions in mm of an open channel shall be A= 200, B= 200, C= 300.

The minimum gradient for an open channel shall be 1:200.

The location of the open channel shall comply with the formation shoulder distance specified in
ESC 410 Earthworks and Formation.

Where track drainage is incorporated within existing track constraints (for example, cuttings,
between tracks) and the shoulder distance cannot be achieved, open channels shall be at an
adequate distance from the track to prevent ballast spill into the channel area. In this case, the
edge of the channel closest to the track shall be a minimum of 2800 mm from the design track
centre. This minimum edge distance shall be increased as required based on track
configuration (rail size, sleeper type, ballast depth) and track curvature.

The top of lined channels shall be no higher than the top of the adjacent track formation(s).

If fibre reinforced concrete is specified, synthetic fibres shall be used.

With multiple tracks, drainage is to be provided by sumps and pipes in the ‘six-foot’ between
each alternate track.

All cess drainage systems shall be designed to discharge to an approved watercourse or

existing drainage system, and the approval of the appropriate authority shall be obtained in
advance of discharge."

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Catch drains

"Catch drains shall be provided on the uphill side of a cutting to divert water from the cutting
face. Drains shall be 1000 mm minimum from the top edge of the cutting.

Catch drains shall be provided on the downhill side of embankments to divert water from the
embankment toe. Drains shall be 1000 mm minimum from the toe of the embankment.

Catch drains may be either lined or unlined depending on the local soil conditions. Half round
pipes or dish drains may be used instead of lined channels.

The location of drains shall comply with the requirements of ESC 410."

Mitre drains

"Where mitre drains are required, they shall be provided at regular centres with a drain located
approximately every 100 m maximum. They shall be installed at the ends of cuttings.

The minimum slope of mitre drains shall be 1 in 200.

The ends of mitre drains shall be splayed to disperse water quickly and reduce scouring."

6.1.2. Subsurface drainage

Subsurface type drains generally consist of a combination of any of the following:

• pipes

• geotextile (or geofabric)

• aggregate filter

• sumps, grates, and sump covers or cages

• inlets and outlets

"Subsurface drains are used where adequate surface drainage cannot be provided due to some
restriction or lack of available fall due to outlet restrictions.

Subsurface drainage shall be provided in locations where the water table is at or near
earthworks level. Subsurface drainage shall also be provided where artesian conditions exist to
relieve water pressure.

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Subsurface drainage shall be provided along the cess, between, across, or under tracks as
required.

Subsurface drainage systems shall be designed to transfer surface runoff, ground water and
seepage, and water collected from other drainage systems to which the new system is being
connected.

If a drainage system is required to remove ground water and seepage, a detailed hydrological
and geotechnical investigation is required to determine the volume of water for the sizing of
drains.

The volume of water from other systems is determined from the outlet capacity of that system."

Pipes

"The capacity of the proposed drainage system shall be determined using the peak flow rate
calculated by the Rational method, with adjustment made for subsurface water and water
collected from other systems. Alternatively, the Hydrograph method may be used. The peak
flow velocity within the pipe shall be less than the manufacturer recommended maximum limits.

Pipes larger than the design size may be adopted to reduce the likelihood of the system
becoming blocked and also enable easier cleaning. The minimum pipe diameter shall be 225
mm (for ease of maintenance).

The gradient of pipes shall be 1 in 100. Where this is not achievable, pipes shall be laid at 1 in
200 minimum.

Depth of pipes under the track shall be 1600 mm minimum from top of rail to top of pipe or pipe
encasing.

Depth of pipes running parallel to the track shall be 600 mm minimum from the design cess
level to top of pipe.

At sites where it is not possible to comply with the pipe depth requirements stated in this section
and achieve an effective drainage system design, the pipe depth may be reduced to the
following:

• 1200 mm minimum from top of rail to top of pipe or pipe encasing for under track pipes

• 300 mm minimum from the design cess level or 1000 mm from top of adjacent rail
(whichever produces the lowest invert level) to top of pipe for pipes running parallel to the
track

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Acceptable pipe materials are as follows:

• reinforced concrete

• fibre reinforced concrete

• steel

Approved proprietary products shall be designed and installed in accordance with the
manufacturer’s specifications.

Steel pipes shall be designed to mitigate the effects of electrolysis and stray track currents.
Designs shall be in accordance with the requirements stated by the Lead Electrical Engineer,
ASA.

Both slotted and unslotted pipes may be used depending on the system type and its means of
collecting and carrying water.

Slotted pipes are preferred, as these do not rely on surface flow between sumps to collect
water.

Slotted pipes and perforated pipes shall not be used for under track pipe work.

Minimum strength requirements are detailed in Table 1. The strength of reinforced concrete and
fibre reinforced concrete pipes shall be determined in accordance with AS/NZ 3725.

Subsurface drainage pipes shall not pass within 10 m of a turnout or crossing.

Table 1 - Acceptable pipe types and minimum strength requirements

Material Type Minimum strength class

Reinforced concrete Slotted and unslotted 4
Fibre reinforced concrete Slotted and unslotted 4
Steel Slotted, perforated and N/A
unslotted
High density polyethylene Slotted, perforated and Only approved products can
(HDPE) pipe unslotted be utilised

If railway live loads are applicable, then the pipes shall be designed for train loads specified in
ESC 310 Underbridges. AS 5100 does not provide guidance on a suitable impact factor for
railway loads distributed on fill. A dynamic load allowance (DLA) shall be adopted which varies
linearly from 1.5 at 0.3 m depth to 1.0 at 3.5 m depth or greater (where the depth is measured
from the top of rail).

Where slotted pipes are used, strength reductions for the slots shall be included in the design
and shall be based on manufacturer’s recommendations.

Pipes located under sections of the rail corridor used for road vehicle access along the rail
corridor, shall be designed for the R20 design load. See Appendix A for details of the R loading
configuration.

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Refer to CV 0205421 – Track Drainage - Typical Sections and Notes for details of typical cross
sections."

After the layout and required capacity of the drain has been established, it is necessary to detail
the various items that will make up the system. This enables the correct components to be
ordered quickly in the construction phase.

Trenching

"The minimum trench width shall be pipe diameter plus 150 mm on each side.

For longitudinal drains located either within 2500 mm of the track centre line or between tracks
where track centres are less than 6000 mm, the minimum trench width shall be pipe diameter
plus 100 mm on each side.

For pipes running in parallel, a clear space of 300 mm between pipes shall be provided to allow
compaction to take place.

Trenches shall be backfilled with suitable material and compacted to not less than 95%
maximum dry density as determined in Test 5.1.1 and Test 5.3.1 (Standard Compaction) of AS
1289.

Reference shall be made to ESC 540 for further requirements on trenching within the rail
corridor."

Pipe bedding type

"When determining the class of pipe to be specified in a subsurface drainage system the
bedding type assumed shall be appropriate for what can be achieved during construction. Most
under track drainage is constructed during track possessions where the more stringent
requirements for placement and compaction of bedding material cannot always be satisfied.

For under track crossings to be constructed during a limited track possession, type ‘U’ bedding
in accordance with AS 3725 shall be used in design."

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Sumps, ballast cages, and covers

"Sumps are required as access points for surface water and for maintenance of the drainage
system.

Sumps shall be spaced at 30 m to 50 m centres, except through platforms where spacing shall
be 20 m to 30 m centres. Reduced centres may be applicable in the 6-foot between tracks to
account for track curvature.

Sumps located adjacent to turnouts shall fit fully between sleepers.

The minimum internal plan dimensions of a sump shall be 600 mm x 600 mm for depths greater
than 1 m. Minimum internal plan dimensions of 450 mm x 450 mm are acceptable for depths
less than 1 m.

Precast sumps with risers used to accommodate varying depths shall be adopted in preference
to cast in-situ sumps.

All sumps shall be provided with a minimum Class D grate in accordance with AS 3996. All
grates shall be galvanised. In addition, for all sumps within 2800 mm of a track centre, or where
site restraints dictate the possibility of ballast covering a pit, a ballast cage (lobster pot) shall be
provided in accordance with CV 0400998. Ballast cages shall be positioned to the outside
edges of the sump. When installed the cages shall not extend above the top of sleeper level.

For locations where access for off-track equipment is limited, sump grates shall be designed for
easy manual removal; for example, grates on a sump shall be manufactured in two sections
rather than one. These grates shall be lockable.

Where the internal sump height (including risers) exceeds 1200 mm, the following shall be
provided:

• step rungs shall be provided at 300 mm vertical centres. If possible, the step runs shall be
located on the face looking at the oncoming train traffic (that is, either Sydney face for the
down track or Country face for up track)

• sump riser heights shall be selected such that step rungs do not come within 50 mm of the
top or bottom of the riser

Where sumps are located in the 6-foot between tracks, the internal dimensions of the sump
shall be increased to a minimum of 600 mm wide (perpendicular to the tracks) x 900 mm to
accommodate inspection access. The width shall be the maximum size available to enable
proper placement of the sump and ballast cage (lobster pot) without clashing with the sleepers.

The internal dimensions of the sump in areas beyond the 6-foot, shall be increased to a
minimum of 900 mm x 900 mm to accommodate inspection access.

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Sumps shall be set out to ensure the minimum amount of pipe cutting is required during
installation (that is, whole pipe lengths shall be used between pits).

Only wet cast concrete pits are permissible. Dry cast concrete pits are not permitted."

Flushing points

"Ground water and seepage (subsoil) drains shall have flushing points. Flushing points shall be
provided generally at intervals of not more than 60 m and at abrupt changes of grade and
alignment. On long and straight pipe runs (for example, straight pipe lengths of 1 km or more)
flushing points can be installed at a maximum interval of 120 m.

Flushing points shall consist of ‘T’ or ‘L’ connections in the subsurface pipe, with pipe
connections extending to the surface for regular flushing with water to clear the subsurface
drain of fouling material."

Aggregate drains

"Aggregate drains are only suitable for use where a small flow of ground water or seepage is
expected. They are not to be used for the collection of surface water.

The design of permeable drains may be carried out using the Darcy-Weisbach equation.

The permeability of clean gravel can range from 0.01 to 1.0 m/s. The aggregates used in
aggregate drains are either 20 mm nominal diameter or 53 mm diameter (ballast). The
permeability of these aggregates is as follows:

• 20 mm aggregate k = 0.15 m/s

• 53 mm aggregate k = 0.40 m/s

Aggregate drains shall be lined with permeable geotextile fabric in accordance with
Section 7.8."

A minimum 100 mm layer of aggregate may be placed on top of the geotextile to protect it from
damage.

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Geotextiles

"The main purpose of a geotextile used in subsurface drainage is to act as a filter, which helps
prevent silting--up of the drain it is protecting. The selected geotextile is to achieve the following
characteristics:

• good permeability through the fabric material

• durability (including the ability to survive during construction)

• good filtering qualities

• resistance to clogging by fine particles

• ability to stretch and conform to the shape of an open trench

An appropriate geotextile filter fabric shall be selected which satisfies both the filtration criteria
suited to the in-situ soil and the site drainage conditions.

The selected geotextile is to exhibit the following mechanical properties as a minimum when
tested in accordance with AS 3706:

• Tear Strength of 400 N

• G Rating of 2000

• Grab Strength of 1100 N

Geotextiles used in subsurface drainage shall fully line the trench and have a minimum lap at
the top of 200 mm but not exceeding 50% of the width at the top. The wrapped trench shall be
covered by a minimum of 100 mm of aggregate."

Inlets and outlets

There are various types of inlets and outlets in use.

Some typical examples of inlets and outlets are rip-rap, grouted rip-rap, sand bags, wire baskets
(that is, gabions and reno mattresses), revetment mattresses, precast concrete units, and cast
in place concrete. Example diagrams can be found in Section 5.2.4.

"To prevent soil erosion, all inlet and outlet points shall be provided with an appropriate size
concrete headwall to suit the ground profile. Refer to CV 0497068 and CV 0497069 for standard
concrete headwalls.

These drawings are not suitable where the face of the headwall is closer than 2150 mm to the
track centreline. These drawings are also not suitable where railway surcharge applies to the

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headwall. In these instances, the concrete headwalls shall be designed by the AEO to provide
strength and stability to resist the applied loadings to AS 5100.

The ground covering at the pipe exit points shall be capable of withstanding the exit flow rates.
The maximum permissible velocities provided in Table 1 shall be used as the ground covering
limits.

Where the sediment load of the water being discharged from a drainage system is high, a silt
trap shall be included."

6.2. Design investigation

Design investigation involves establishing the scope of the investigation and the type and
characteristics of drainage system required.

6.2.1. Scope of investigation

The main objective of a design investigation is to establish the requirements of the drainage
system and any restrictions that may be imposed on the system.

Aspects to be covered in the design investigation include the following:

• identification of the problem and therefore the drainage objective. That is, what area is to
be drained and for what reason.

• determination of the information required. That is, location, outside influences, fall
available, possible outlets, access, site safety requirements, and so forth)

• collection and study of all available existing information

All available information from adjacent sites or the locality in general should be studied
before embarking on any fieldwork. This will often save unnecessary fieldwork or may point
out particular problems or aspects that should receive special attention.

Included in this stage should be a full service search. This involves the check of the
location of both TfNSW and public services. This may also involve site inspections with
representatives from various bodies to accurately locate services, the position of which
should then be marked, either on a plan or pegged.

Other types of information that may be of use are aerial photographs, maps (topographic,
geological, soil, and so forth), charts, and meteorological and hydrological information.

• site inspection

A checklist should be prepared prior to the actual investigation so that the maximum
amount of information may be extracted from the site in a minimum time (see the form in
Appendix C).

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Items that should be looked at during a site inspection include the following:

o access to and from the proposed site and any possible restrictions

o type and location of any existing drainage systems and any possible reasons for its
failure

o the position and condition of any existing drainage outlets

o any other likely drainage outlets. Determine the outlet conditions and any likely
restrictions because these may affect the design of the drainage system.

o adjacent structures that may impact on the drainage design, or where the drainage
design may cause instability to the structure

• catchment area estimation

The catchment area for the drainage system needs to be estimated during the site
inspection. This may be checked by comparison with maps of the area.

A further inspection may be required at a later stage so that the area may be surveyed to
establish the available fall and invert level for the inlet and outlet.

6.2.2. Determination of the type of drainage system required

On completion of the design investigation, information gathered will be compiled and a decision
made on the type of drainage system that is most suitable.

The type of system chosen for each location is dependent on the site restraints, water source,
track structure, and long-term maintenance issues. The two types of drainage systems are
surface and subsurface.

If possible, surface drains should be used in preference to subsurface drains since surface
drains are easily inspected and maintained.

Note: care needs to be taken to ensure that the right drainage system is designed for
each location. For example, using a slotted system to drain surface run-off that could
have been collected by sumps may not be the best solution. This could lead to a
quicker failure of the system by allowing an easier route for water to pass (seep) into
the formation.

6.3. Estimation of the required drainage system capacity

At this point, the site requirements and restrictions, the drainage type, and the layout of the
proposed drainage system should be known.

The next step is to estimate the quantity of water that the drain will need to carry, so that the
size of the drain and its various components may be determined.

The quantity of water (QPF) that the drain is required to carry generally is given by Equation 1.

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QPF = QR + QS + QC

Equation 1 - Quantity of water that a drain is required to carry at peak flow

Where:
3
QPF = water quantity (m /s or l/s)
3
QR = run-off quantity collected (m /s or l/s)
3
QS = subsurface water quantity intercepted (m /s or l/s)
3
QC = collected water quantity from a drain of a connecting system (m /s or l/s)

The calculated quantity (QPF) represents the peak flow that the drain will be required to carry, for
a short time only.

The quantity (QR) is calculated for the catchment size and critical rainfall duration by using the
Rational method. Alternatively, the Hydrograph method may be used.

The value of intercepted subsurface water 'QS' is difficult to determine. If a drainage system is
required to remove intercepted subsurface water, a detailed hydrological investigation or
geotechnical investigation, or both is usually required.

The volume of water conducted from other systems, 'QC', is estimated from the outlet capacity
of the system to which the new system is being connected. Provided the catchment area, drain
size, and slope are known (or can be measured), the maximum value of 'QC' can be determined
using the Rational method. This information may also be available from the authority owning the
asset (such as a council).

If the connecting system is a complex network of drainage, a detailed study may be required.

Account needs to be taken of all water flowing onto the rail corridor from adjoining properties
and streets.

6.3.1. Average recurrence interval (ARI)

To use the Rational method, it is necessary to adopt a relevant average recurrence interval
(ARI). This is an approximate estimate of how often a particular event will occur on average. For
example, an ARI of 1 in 50 years means that a particular storm event is likely to occur on
average only once in every fifty years.

6.3.2. The Rational method

The Rational method provides a method for calculating the peak rate of discharge of a storm
event for a specific ARI.

If incorporating computer modelling in the design process, then a range of storm events
representing varying rainfall duration needs to be investigated. The drainage design will be
carried out adopting the critical rainfall event.

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Hydrology and hydraulic computer packages can be utilised for the design of track drainage.
The following procedure deals with hand calculation methods only.

The Rational method is detailed fully in Australian Rainfall and Runoff (AR&R) published by the
Institution of Engineers, Australia.

The AR&R publication recommends the following steps for flow rate determination for sites in
eastern New South Wales.

The form in Appendix D breaks down these steps and can be used as a calculation sheet.

1. calculate the critical rainfall duration (tC) for the area under investigation

Two methods may be adopted to calculate the critical rainfall duration. These methods are
the following:

• equal area stream slope - recommended for hilly or undulating sites as it gives a more
realistic flow response time (refer to AR&R for this procedure)

• basic formulae (for Eastern New South Wales), given by Equation 2.

0.38
tC = 0.76 A

Equation 2 - Critical rainfall duration - basic formula for Eastern NSW

Where:

tC = critical rainfall duration (in hours)

2
A = catchment area (km )

The catchment areas required for peak flow rate calculations need to be determined
using (in order of preference) site survey, site measurements, or suitably scaled
topographic maps.

2. calculate the critical 50 year design rainfall intensity (Icr,50)

This step comprises of looking up a series of basic rainfall intensities, skewness factors, and
geographical factors from contour style maps found in Volume 2 of the AR&R guide.

These values can be plotted on a log-Pearson Type III diagram (LPIII) or incorporated in
interpolation formulas found in Book 2 of AR&R volume 1.

From either of these two methods the 50 year design rainfall intensity ‘Icr,50’ for the critical
duration tC can be determined.

3. determine the 50 year run-off coefficient (C50) for the geographical area by determining the
following:

• read the 10 year run-off coefficient value (C10) from Figure 1.1 in Volume 2 of the AR&R

• geographical zone B is adopted from Figure 1.2 (AR&R) – for Sydney Metropolitan Area

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• interpolate or calculate the 50 year frequency factor FF50 from Table 1.1 (AR&R) based
on site elevation

• calculate C50 = C10 x FF50 (no units)

4. calculate the 50 year peak flow rate (Q50)

Adopt the Rational method formula.

Q50 = F × C50 × Icr,50 × A

Equation 3 - Rational method formula

Where:
3
Q50 = peak flow rate (m /s) for ARI = 50 years

F = conversion factor to balance units used.

2
= 0.278 if A is in km

= 0.000278 if A is in hectares (ha)

C50 = run-off co-efficient for ARI = 50 years

Icr,50 = average rainfall intensity (mm/h) for the critical duration

2
A = catchment area (km or ha)

The peak flow rate is used in determining how much water is likely to rain onto a catchment and
therefore enabling the sizing of the drainage system under consideration.

6.4. Surface drain design

The following steps can be used to determine correctly the required size of surface drainage.

6.4.1. Step A: Determine the required channel capacity

Prior to estimating the size of a surface drain, the required capacity either needs to be known or
calculated using Equation 1.

For surface drains, 'QS' and 'QC' can usually be neglected. In this case, Equation 1 becomes QPF
3
= QR = Peak flow rate (m /s).

Example 1
3
A rainfall run-off quantity of 0.15 m /s was calculated to act on a catchment for the 50 year ARI
critical duration storm (from the 'Rational method'). There is no subsurface water intercepted,
3
but a nearby stormwater pipeline enters the channel and adds 0.07 m /s. What is the total water
quantity the channel will need to be designed for?

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Solution 1
The design flow capacity can be determined from Equation 1.
3
QPF = QR + QS + QC = 0.15 + 0 + 0.07 = 0.22 m /s.
3
The channel will need to be sized to take a 0.22 m /s flow rate or greater.

6.4.2. Step B: Select a Manning's roughness coefficient

A value of the roughness coefficient 'n' can then be selected from Table 2, Table 3, Table 4,
Table 5, or Table 6, depending on the pipe or channel type.

Table 2 - Manning's roughness coefficient - closed conduits

Channel material Roughness coefficient ‘n’

concrete pipe or box 0.012
corrugated steel pipe - helical 0.020
vitrified clay pipe 0.012
fibre cement pipe 0.010
P.V.C. pipe 0.009
steel pipe 0.009 - 0.011

Table 3 – Manning's roughness coefficient - lined open channels

Channel material Roughness coefficient ‘n’

concrete lining 0.013 - 0.017
gravel bottom concrete sides 0.017 - 0.020
gravel bottom rip rap sides 0.023 - 0.033
asphalt rough 0.016
asphalt smooth 0.013

Table 4 - Manning's roughness coefficient - unlined channels - earth uniform section

Channel material Roughness coefficient ‘n’

clean channel 0.016 - 0.018
with short grass 0.022 - 0.027
gravelly soil 0.022 - 0.025

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Table 5 - Manning's roughness coefficient - unlined channels - earth fairly uniform

section

Channel material Roughness coefficient ‘n’

no vegetation 0.022 - 0.025
grass plus some weeds 0.030 - 0.035
dense weeds 0.030 - 0.035
clean sides gravel bottom 0.025 - 0.030
clean sides cobble bottom 0.030 - 0.040

Table 6 - Manning's roughness coefficient - rock

Channel material Roughness coefficient ‘n’

smooth and uniform 0.035 - 0.040
jagged and irregular 0.040 - 0.045

6.4.3. Step C: Determine the slope of the drain

The minimum slope of a drain is 1 in 200 (that is, 1 m fall vertically for every 200 m horizontally),
though a minimum slope of 1 in 100 is preferred for self-cleaning purposes. It should be noted
that as the slope of the drain becomes flatter, the tendency for a drain to become blocked due
to sediment build-up increases. Consequently, the maintenance of the drain also increases.

6.4.4. Step D: Select a trial channel size

Using the value of slope 'S' and the roughness coefficient 'n' selected previously, the capacity of
the trial drain can be calculated using Equation 4 (Manning's equation) or a simplified version
(Equation 5).
0.67 0.5
Q = (1/n) × A × R ×S

Equation 4 - Manning's equation

Where:
3
Q = flow rate or capacity (m /s)

n = roughness co-efficient. From Table 2, Table 3, Table 4, Table 5, or Table 6

A = channel cross-sectional area

R = hydraulic radius - examples given in Table 7

R = A/P where P = wetted perimeter (that is, the surface in contact with the water)

S = slope of the drain

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0.67
If X = A x R then Equation 4 becomes:
0.5
Q = (1/n) × X × S

Equation 5 - Simplified version of Manning's equation

See Table 7 for values of 'X' for various channels. See Figure 26 - Channel types for a review of
the trapezoidal and rectangular channel types referred to in Table 7.

Table 7 - Calculation of X for various channel sizes

No. Channel Channel Channel Area Wetted Hydraulic X

2
dimension dimension dimension (m ) perimeter radius (m) (eqn 5)
(mm) for A (mm) for B (mm) for C (m)
1 200 - 300 0.060 0.700 0.086 0.012

2 200 - 450 0.090 0.850 0.106 0.020

3 200 200 300 0.100 0.860 0.115 0.024
4 200 300 300 0.120 1.021 0.118 0.029
5 200 200 450 0.130 1.016 0.128 0.033
6 300 - 450 0.135 1.050 0.129 0.034
7 300 200 300 0.150 1.021 0.147 0.042
8 300 300 300 0.180 1.149 0.157 0.052
9 450 - 450 0.203 1.350 0.150 0.057
10 300 200 450 0.195 1.171 0.167 0.059
11 300 450 300 0.225 1.382 0.163 0.067
12 300 300 450 0.225 1.299 0.173 0.070
13 300 200 600 0.240 1.321 0.182 0.077
14 300 450 450 0.270 1.532 0.176 0.085
15 450 - 600 0.270 1.500 0.180 0.086
16 300 300 600 0.270 1.449 0.186 0.088
17 300 450 600 0.315 1.682 0.187 0.103
18 300 200 900 0.330 1.621 0.204 0.114
19 450 300 450 0.338 1.532 0.220 0.123
20 300 300 900 0.360 1.749 0.206 0.125
21 450 - 900 0.405 1.800 0.225 0.150
22 450 450 450 0.405 1.723 0.235 0.154
23 450 300 600 0.405 1.682 0.241 0.157
24 300 450 900 0.405 1.441 0.281 0.174
25 450 450 600 0.473 1.873 0.252 0.188
26 450 300 900 0.540 1.982 0.272 0.227

27 450 450 900 0.608 2.173 0.280 0.260

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No. Channel Channel Channel Area Wetted Hydraulic X

2
dimension dimension dimension (m ) perimeter radius (m) (eqn 5)
(mm) for A (mm) for B (mm) for C (m)
28 600 600 600 0.720 2.297 0.313 0.332

29 600 600 900 0.900 2.597 0.347 0.440

Note: Smaller channels tend to become blocked with built up sediment very quickly.

The following are typical examples of calculations to determine the capacity of an open channel.

Example 2
For a trapezoidal channel (shown in Figure 27 below) with a slope of 1 in 200 and a roughness
coefficient 'n' of 0.030. Calculate the channel capacity using a) Equation 4 and b) Equation 5
and Table 7:

Figure 27 - Sample trapezoidal channel

Solution 2a) - using Equation 4

S = 1 in 200 = 0.005

n = 0.030

A = (600 × 300) + 2 × (0.5 × 300 × 450)

2
A = 315,000 mm
2
A = 0.315 m

R = A/P

P = 2 ×√((300)×2+(450)×2)+600

P = 1682 mm

P = 1.682 m

R = 0.315/1.682

R = 0.187 m

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0.67 0.5
Q = 1/n × A × R S
0.67 0.5
Q = 1/0.03 × 0.315 × (0.187) × (0.005)
3
Q = 0.243 (m /s)

Solution 2b) - using Equation 5 and Table 7

S = 0.005

n = 0.030

From Table 7, X = 0.103

Equation 5
0.5
Q = 1/n ×X × S
0.5
Q = 1/0.03 × (0.103) × (0.005)
3
Q = 0.243 (m /s)

6.4.5. Step E: Check channel capacities

Once the capacity of the trial drain is determined 'Q' it will be compared with the required
capacity found using Equation 1 'QPF'. If the capacity of the trial drain 'QPF' is considerably
greater or lesser than the required capacity 'Q', then a new trial drain should be selected and
steps (c) and (d) repeated until the trial capacity is approximately equal to or slightly greater
than the required capacity.

Example 3
Check that the channel in Example 2 has sufficient capacity to cater for the design storm as
calculated in Example 1.

Solution 3
3
The channel capacity 'Q' of 0.243 m /s (Example 2) is greater than the design storm flow rate
3
'QPF' of 0.220 m /s (Example 1). Therefore, it has sufficient capacity.

6.4.6. Step F: Calculate water velocities

Once the required capacity is obtained, the flow velocity of water within the channel may be
calculated.

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The velocity is calculated using Equation 6 as shown below:

V=Q/A

Equation 6 - Flow velocity of water

Where:

V = velocity (m/s)
3
Q = flow rate (m /s) calculated using Equation 1
2
A = area of selected channel (m )

Example 4
Calculate the flow velocity of water within the channel in Example 2.

Solution 4
3
Q = 0.22 m /s
2
A = 0.315 m (from example 1 - assumed flowing full)

V = Q/A = 0.220/0.315 = 0.69 m/s

6.4.7. Step G: Check channel lining

In some cases, it may only be possible to install a small drain and the flow through this drain
may have a velocity greater than the maximum permissible velocity, and consequently the
channel needs to be lined.

Table 8 gives the maximum permissible velocity of varying ground coverings.

Table 8 - Maximum permissible velocities for various types of channel lining

Channel type Velocity (m/s)

Fine sand 0.45
Silt loam 0.60
Fine gravel 0.75
Stiff clay 0.90
Coarse gravel 1.20
Shale, hardpan 1.50
Grass Covered 1.8
Stones 2.5
Asphalt 3.0
Boulders 5.0
Concrete 6.0

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Lining a channel changes the roughness coefficient 'n', and therefore the capacity of the
channel may be altered either up or down (See Table 3, Table 4, Table 5, and Table 6).

A lining is selected such that the allowable velocity for the type of lining is greater than that
calculated in step F. This is used as a first trial value.

Example 5
The channel in example 4 is lined with grass covering. Is it sufficient to withstand the flow
velocity?

Solution 5
Velocity of water in channel = 0.69 m/s (solution 4).

The maximum permissible velocity of grass lining = 1.8 m/s (Table 8).

Therefore, grass has the required resistance and the lining is sufficient.

6.4.8. Step H: Completion

If the capacity of the channel is inadequate or the ground cover velocity insufficient then
modifying the channel size, slope, or lining type will need to be done until all aspects are
satisfactory.

6.4.9. Complete example

The following is a complete example.

Example 6
Calculate the required channel size and lining type given that the required capacity of the
3
channel is 0.40 m /s. The existing soil is clay.

Solution 6:
Trial 1:
3
Step A: No subsurface water or connecting system. So QPF =0.40 m /s

Step B: n=0.016 (Table 3, Table 4, Table 5, and Table 6)

Step C: Adopt S=0.01 (desirable minimum slope)

2
Step D: Select channel no. 14 from Table 7. A = 0.270 m . X = 0.085
0.5 0.5 3
Q = 1/n ×X × S = (1/0.016) × (0.085) × (0.01) = 0.53 m /s (Equation 5)
3 3
Step E: Channel capacity 0.53 m /s > design capacity 0.40 m /s. Okay.

Step F: V = Q/A = 0.40/0.270 = 1.48 m/s (Equation 6)

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Step G: Clay has permissible velocity capacity of 0.9 m/s (Table 8) which is less than the design
flow of 1.48 m/s. Could modify size or change lining. Opt for a change of lining type to grass
covered (capacity 1.8 m/s).

Step H: Need to redo calculations, as n will change

Trial 2: Try lining with higher permissible velocity – say grass lining
3
Steps A, B & C: QPF =0.40 m /s. n=0.024 (Table 7). S=0.01
2
Step D: Same channel no. 14 from Table 7. A = 0.270 m . X = 0.085
0.5 3
Q= (1/0.024) × (0.085) × (0.01) = 0.35 m /s (Equation 5)
3
< 0.4m /s therefore no good. Could modify size or change lining.

Trial 3: Try smoother lining, with high permissible velocity - say asphalt
3
Steps A, B & C: QPF =0.40 m /s. n=0.013 (Table 7). S=0.01
2
Step D: Same channel no. 14 from Table 7. A = 0.270 m . X = 0.085
0.5 3
Q = (1/0.013) × (0.085) × (0.01) = 0.65 m /s (Equation 5)
3 3
Step E: Channel capacity 0.65 m /s > design capacity 0.40 m /s. Okay.

Step F: V = Q/A = 0.40/0.270= 1.48 m/s (Equation 6)

Step G: Asphalt has capacity of 3.0 m/s (Table 8) which is greater than the design flow of
1.48 m/s. Therefore, it is satisfactory.

Step H: Channel no. 14 laid in bitumen at a 1% slope is satisfactory.

6.5. Subsurface drain design

Subsurface drain design involves calculating the required size of pipe drains and aggregate
drains, taking into consideration capacity, type, roughness coefficient, slope, strength, and
environment.

6.5.1. Pipe drains

The following steps can be used to determine correctly the required size of subsurface drainage
pipes:

Step A: Determine the required pipe capacity

Prior to estimating the size of a subsurface drain, the required capacity will either be known or
calculated using Equation 1. Refer to Section 6.3 for more detail.

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Step B: Select the pipe type

The pipe type selected should be adopted based on the suitability of the system to the site.
Unslotted pipes will be used for undertrack pipes, whereas either slotted or unslotted pipes can
be used elsewhere.

Acceptable pipe materials by type are detailed in Table 1.

Step C: Adopt a Manning's roughness coefficient

A value for pipe roughness 'n' can be obtained from the manufacturer for the product being
adopted. Table 3, Table 4, Table 5, and Table 6 detail typical values that are also acceptable.

Step D: Determine the slope of the pipe

The pipe slope will be determined from the geometry of the site to best suit site constraints.
However, the minimum pipe slope is 1 in 300 (although a slope of 1 in 100 is preferable for self-
cleaning purposes). The steeper the slope, the lesser the maintenance requirements.

Step E: Select a pipe size

A trial pipe size can be found using Table 9 by selecting a pipe where 'Q' is greater than the
peak flow required 'QPF'.

Alternatively, the capacity of the pipe can be found by using Manning's Equation (Equation 4).

Table 9 - Capacities for various pipe types and sizes. L

Pipe diameter Pipe material Drain slope Max flow Q (l/s)

225 F.C. 1 in 100 58.3
225 F.C. 1 in 200 41.2
225 Concrete 1 in 100 53. 0
225 Concrete 1 in 200 37.4
300 F.C. 1 in 100 125.6
300 F.C. 1 in 200 88.8
300 Steel 1 in 100 104.6
300 Steel 1 in 200 74.0
300 Concrete 1 in 100 114.1
300 Concrete 1 in 200 80.7
375 F.C. 1 in 100 227.7
375 F.C. 1 in 200 161.0
375 Steel 1 in 100 175.1
375 Steel 1 in 200 123.8
375 Concrete 1 in 100 207.0
375 Concrete 1 in 200 146.6

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Pipe diameter Pipe material Drain slope Max flow Q (l/s)

450 F.C. 1 in 100 370.3
450 F.C. 1 in 200 261.8
450 Steel 1 in 100 264.5
450 Steel 1 in 200 187.0
450 Concrete 1 in 100 336.6
450 Concrete 1 in 200 238.0
525 F.C 1 in 100 558.7
525 F.C 1 in 200 395.0
525 Concrete 1 in 100 507.9
525 Concrete 1 in 200 359.1
600 F.C. 1 in 100 797.7
600 F.C. 1 in 200 564.0
600 Steel 1 in 100 498.5
600 Steel 1 in 200 352.5
600 Concrete 1 in 100 725.1
600 Concrete 1 in 200 512.7

Notes to Table 9

1. FC = fibre cement pipe

2. Steel = corrugated steel pipe

3. Concrete = concrete or vitrified clay pipe

4. PVC pipes are not to be used for track drainage design. They are included in
Table 9 for assessment of existing pipe systems.
3
5. To convert m /s to l/s multiply by 1000 (that is, 1000 litres = 1 cubic metre)

6. The values of Manning's roughness co-efficient used in the calculations for the
values given in Table 8 are as follows:

• concrete: n = 0.011

• fibre Cement: n = 0.010

• P.V.C.: n = 0.009

• steel (100 - 300 dia): n = 0.012

• steel (375 dia): n = 0.013

• steel (450 dia): n = 0.014

• steel (600 dia): n = 0.015

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Step F: Check the flow rates within the pipe

Using Equation 5 (V=Q/A), the velocity of flow within the pipe can be determined. The flow
velocity within the pipe needs to be at an acceptable level so as not to cause damage to the
pipe surface. The manufacturer has recommended maximum limits.

Step G: Determine the strength of the pipe (pipe class)

The pipe needs to be checked to see if it is suitable for the design and construction loads that
are imposed on it. The method of calculation of pipe strength is to follow the relevant Australian
Standard (for example, AS 3725 Design for installation of buried concrete pipes).

If pipes are within a 45 degree projection of the outside of the sleeper (in any direction), then
railway loading needs to be included. Dynamic loads will also be applied – Refer to
Section 6.1.2.

If pipes are situated within a 45 degree projection of the outside of an access road (in any
direction) then the loads applicable to the access vehicle need to be included. Dynamic loads
will also be applied – Refer to Section 6.1.2.

Pipe strength is also highly dependent on the type of trench excavation, fill material, and
compaction technique. When determining the class of pipe to be specified in a drainage system,
type 'U' bedding should be assumed, even if better bedding is specified on the drawings. Most
track drainage is constructed during track possessions where the specified placement and
compaction of bedding material cannot always be achieved.

Where slotted pipes are used, strength reductions for the slots need to be included in the design
and will be based on manufacturer’s recommendations.

Manufacturer supplied computer software is acceptable for this purpose of pipe strength design,
provided it is in accordance with AS 3725.

Minimum strength requirements are detailed in Table 1.

Complete example:
Example 7
3
A rainfall run-off quantity of 0.10 m /s was calculated to act on a catchment for the 50 year
average recurrence interval (ARI) critical duration storm (from the Rational method). There is no
subsurface water intercepted, but a nearby stormwater pipeline enters the system and adds
3
0.02 m /s. What size reinforced concrete pipe is required to satisfy flow requirements?

Solution 7

Step A: The design flow capacity can be determined from Equation 1

3
QPF = QR + QS + QC = 0.10 + 0 + 0.02 = 0.12 m /s

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Step B: Reinforced concrete (given)

Step C: Roughness n=0.011 (from Table 9 – notes)

Step D: Pipe slope 1 in 200 (given)

3
Step E: From Table 9, a 375 mm diameter RC pipe has capacity of 146.6 l/s (0.146 m /s) which
is greater than the design flow capacity. In addition, the size is greater than the 225 mm
minimum.

Step F: Flow rate within the pipe V=Q/A = 0.12/(3.142 × 0.375 × 0.375/4) = 1.1 m/s which is less
than the acceptable limit for concrete (6 m/s). Therefore, okay.

6.5.2. Aggregate drains

Aggregate drains are only suitable for use where small flow or seepage is expected. If a larger
flow is expected, a slotted pipe should be added to the system, and then the drain should be
sized as described previously. A typical example of an aggregate drain is a blanket drain.
Another type of aggregate drain is a French drain.

Aggregate drains are to be lined with a geotextile.

The capacity of an aggregate drain may be determined using Darcy's equation (Equation 7).

Q=k×i×A

Equation 7 - Darcy's equation

Where:
3
Q = flow (m /s)

k = permeability of the aggregate

i = hydraulic gradient or slope

2
A = cross-sectional area (m )

The permeability of clean gravel can range from 0.01 m/s to 1.0 m/s. The aggregates used in
aggregate drains are either 20 mm nominal diameter or 53 mm diameter (ballast). The
permeability of these aggregates is:

20 mm aggregate - k = 0.15 m/s

53 mm aggregate - k = 0.40 m/s

Equation 7 may be simplified if K = k × i, and Equation 8 becomes:

Q=K×A

Equation 8 - Simplified version of Darcy's equation

Table 10 gives values for 'K' for use in Equation 8 to determine the capacity of aggregate drains.

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Table 10 - Values of K = k × i for various slopes

Slope K = k × i (m/s), applied to K = k × i (m/s), applied to

20 mm 53 mm
1 in 100 0.00150 0.0040
1 in 200 0.00075 0.0020
1 in 300 0.00050 0.0013
1 in 400 0.00038 0.0010
1 in 500 0.00030 0.0008

Example 8
3
If Q = 0.01 m /s or 10 l/s an aggregate drain using 20 mm aggregate at a slope of 1 in 200, what
size drain is required?

Solution 8

Q = K × A, this may be rearranged to: A = Q/K

Therefore:

A = 0.01 / 0.00075
2
A = 13.3 m

For the same flow using 53 mm aggregate at a slope of 1 in 200, the area required is:

A = 0.01 / 0.002
2
A = 5.0 m

6.6. Other design considerations

"When selecting a pipe, the type of environment (whether, the water is abrasive, acidic or
alkaline) shall be considered. The manufacturer's specifications shall be referred to in relation to
the various environmental conditions and circumstances for which the pipe is deemed to be
suitable.

The possible effects of non-standard ballast profiles, other track infrastructure and track
geometry shall be considered.

The configuration issues arising from placing straight pipes alongside curved tracks shall be
considered (for example, this situation may require reduced sump centres).

The permanent effects of the drainage system located alongside existing structures such as
overhead wiring structures, retaining walls, platforms, embankments, shall be taken into
account. The likelihood of destabilising an existing structure during the excavation stage shall
also be identified and accounted for.

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Potential conflicts with existing services shall be considered. Service searches shall be
conducted and the locations of these services indicated on the design documentation. Service
searches shall be supplemented by trial pits to ensure the accuracy of the service search
information and determine the depths of the services."

7. Construction of track drainage

This section deals briefly with the various forms of drainage construction.

One important consideration is that each site needs to be assessed on its own merits. No two
sites are the same. This will be taken into account when selecting the site protection,
equipment, and personnel required for each particular site.

This section discusses the various steps involved in the construction of both surface and
subsurface drainage systems.

7.1. Line and grade

The line and grade of the drainage system, be it surface or subsurface, may be set out by one
or a combination of the following methods:

i. stakes, spikes, shiners (small reflective metal discs), marks, or crosses set at the surface
on an offset from the desired centre line

ii. stakes set in the trench bottom on the pipeline as the rough grade for the pipe is completed

iii. elevations given for the finished trench grade and pipe invert while laying the pipe or
excavating the trench is in progress

Of these three methods, method (i) is the most commonly used for track drainage.

Method (i) involves stakes, spikes, shiners, or crosses being set on the opposite side of the
trench from where the excavated material is to be cast at a uniform offset, in so far as
practicable, from the drain’s centreline. A table known as a cut sheet is prepared. This is a
tabulation of the reference points giving the offset and vertical distance from the reference point
to either: the trench bottom, the pipe invert, or both. When laying the pipe it may be more
practical to give two vertical distances, one to the trench bottom (excavation depth), and one to
the top of the pipe, which is generally easier to measure to than the pipe invert. The grade and
line may be transferred to the bottom of the trench by using batter boards, a tape and level, or
patented bar tape and plumb bob unit.

This method may be adapted to suit. For example, it is common practice to have the proposed
route surveyed with the reference points marked on the datum rail (either the down rail or the
low rail on a curve). The offset and vertical height may be easily transferred from the rail by use
of a straight edge, spirit level, and tape (see Figure 28).

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Figure 28 - Method of measuring the depth of a trench and offset to pipe centreline

If the track is on a constant grade that is suitable for the pipeline and trench, this grade may be
adopted. This gives a constant vertical depth from the datum rail to the trench bottom and
pipeline, making construction and grade control much easier.

Another method of controlling the line and grade is the use of lasers. A laser beam is passed
through the centre of the pipeline at the desired grade. It strikes opaque targets attached to the
end of the pipe, and the pipe may then be either lifted (packed) or lowered until the laser passes
through the centre of the target.

7.2. Site preparation

The amount of preparation varies from site to site. Operations that should be classified as site
preparation are the following:

• clearing

• removal of unsuitable soils

• preparation of access roads

• detours and bypasses

• improvements to and modification of existing drainage

• location, and protection or relocation of existing utilities

The success of the construction phase depends to a great degree on the thoroughness of the
planning and the execution of the site preparation work.

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7.3. Excavation
With favourable ground conditions, excavation can be accomplished in one simple operation.
Under conditions that are more adverse, it may require several steps, such as clearing, rock
breaking, ripping or blasting, and excavation. When excavating for a pipeline, the trench at and
below the top of the pipe should be wide enough to ensure adequate compaction on the sides
of the pipe can be achieved. The minimum width on either side of the pipe will be in accordance
with Section 6.1.2.

The amount of excavation and the types of equipment required may vary, so each site needs to
be assessed on its merits to determine the type and quantity of equipment necessary.

Excavation near structures or platforms will comply with TMC 411 Earthworks.

Particular conditions that should be taken into account when selecting equipment are the
following:

• site access

• size and amount of excavation necessary

• site conditions, that is, firm or boggy ground conditions

• location and availability of plant

• whether the plant item required has to be floated to the site (if so the offloading conditions
and a suitable area should be checked)

• services in the area

Typical items of plant (equipment) utilised are the following:

• gradall (normal or highrail)

• backhoe

• tiltable dozers

• graders

• front end loaders

• tracked excavators

• hydraulic excavators

• bogie tippers and 4WD dumpers

7.4. Surface drain construction

Surface drains remove surface water from near the tracks, and construction of the drains
involves surveying, excavating, and (where needed) lining of channels.

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7.4.1. Requirements
The main purpose of surface drains is to remove surface water from near the tracks and
disperse it as quickly as possible. To do this, the drainage trench or ditch should be constructed
at a uniform even grade, with no low sections where water may pond and seep into track
formation, thereby defeating the purpose of the drainage system.

The grade of the drainage trench should be a minimum of 1 in 200 where practicable. Flatter
grades may be used but require more regular inspection and maintenance, since they tend to
become blocked with sediment more quickly than drains with steeper grades.

Where the velocity of the water is greater than that shown in Table 8 in Section 6.4, some form
of scour protection is required, for example, lining the channel. Where doubts exist as to the
erodability of a soil, the Lead Civil Engineer at ASA needs to be consulted. Where any surfaces
are cleared of vegetation, these areas will be re-vegetated at the end of construction, to prevent
unnecessary build-up of silt in nearby drains.

7.4.2. Construction steps

The steps involved in construction of surface drains are the following:

• Survey the proposed drainage route. This may be carried out during the preliminary
investigation.

• Establish and mark out reference points for use during construction. Marking out may
consist of paint marks on the datum rail or star pickets. The interval used for the reference
marks depends on the length of the drainage system. For example, for a short drain the
interval may be five metres.

• Clear the site. This should be part of any site preparation work carried out. This may
involve relocation of signal troughing, clearing vegetation, and so forth.

• Excavate to required level. When excavating the trench, use a bucket width equal to the
width of the trench base, then add a batter to the sides of the trench formed. Monitor
excavation with the method described in Section 7.1. Once the trench has been
constructed, level and compact the trench base making sure that no low points exist.

• Check for risk of erosion. If this is expected to be high, the drain may require lining.

• Clean up the site and re-vegetate any denuded slopes.

Note: It is good practice to work from the lowest to the highest point. That way, if work
is interrupted for any reason, at least part of the drainage system will function correctly
if it rains before completion.

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7.5. Subsurface drain construction

The following sections detail construction methods for the following subsurface drains:

• longitudinal drains

• lateral drains

• blanket drains

• horizontal and vertical drains

• pipe drain using unslotted pipes

• sump installation

7.5.1. Longitudinal drain construction

This is the most commonly used form of subsurface drain used for track drainage. The basic
construction steps are as follows:

i. survey the site

ii. establish the reference points. These may be paint marks on the rails or star pickets. The
purpose of these marks is to provide points from which the depth of the trench and pipe
invert level may be measured accurately. (See Section 7.1).

iii. excavate to the desired level. The type of equipment used to excavate the trench differs
from location to location, depending on such parameters as access, material, volume to be
excavated, and clearances for the safe operation of equipment.

iv. the depth of the excavation depends on the pipe location, and outlet and inlet
requirements. For pipes running parallel to the track, the minimum pipe cover is to be
600 mm below the design cess level. Where this is not feasible, the minimum pipe cover is
to be 300 mm below the design cess level or 1000 mm below the adjacent rail level
(whichever produces the lowest invert level). The design track formation profile will be as
set out in TMC 411. The width of trenches should only be as wide as necessary to ensure
proper installation and side compaction. The minimum width will be pipe diameter plus
150 mm on each side. For longitudinal drains located either within 2500 mm of the track
centre line or between tracks where track centres are less than 6000 mm, the minimum
trench width will be pipe diameter plus 100 mm on each side. See Figure 29 for a visual
representation of these width requirements. A vertical sided trench with no support may
only be suitable for a shallow trench. Geotechnical advice may be sought to determine if
shoring or benching is required for certain ground conditions or deeper trenches.

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Figure 29 - Trench width

The method of installing this type of subsoil drain depends on the type of subsoil and other
conditions encountered, such as the following:

i. impervious soil - aggregate filled excavation (that is, most clays are relatively impervious).
Refer also to Figure 15.

a. lay the geotextile in the bottom of the trench. Where joints need to be made in the
geotextile a minimum overlap of 1 m should be made.

b. place a layer of aggregate in the bottom of the trench approximately 50 mm thick. The
aggregate used for this should be 20 mm nominal diameter aggregate.

c. lay the pipe sections, one section at a time, on top of the aggregate

d. place pits or sumps or both, and remove knockouts

e. check and adjust the pipe level and grade if necessary by packing aggregate under
the pipe

f. place aggregate around and over the pipe, tamping the aggregate on the sides of the
pipe as the trench is filled. Once the pipe is covered, complete the filling of the trench
compacting the aggregate in layers no greater than 150 mm thick, using a vibrating
plate compactor or similar.

g. fold geotextile over the top of the trench, ensuring that the ends are overlapped a
minimum of 300 mm

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h. place a minimum 100 mm thick layer of aggregate over the geotextile and grade the
surface

i. pack knockouts from the inside of the pits using sand or cement mortar (or geotextile if
detailed in this manner)

j. complete associated works (for example, pit lids or pots, ballasting, and so forth)

ii. pervious soil – aggregate filled excavation (for example sandy soils). Refer also to
Figure 16.

When laying a drain in pervious soil, it is necessary to place an impervious layer in the
base of the trench. Typical impervious layers are concrete, cement or lime stabilised fill, or
clay fill. The impervious layer is to be 100 mm thick at the edges of the trench and slope
towards the centre of the trench, where it is to be 50 mm thick. Once an impervious layer is
installed, the remaining construction steps are the same as steps '(a)' to '(j)' for drains in
impervious soils above.

iii. geotextile wrapped pipes

Sometimes it is beneficial to wrap the pipe inside a geotextile rather than around the
outside of a trench. In this case, repeat the procedure of point 'i' with the exception of: step
'a', the geotextile is wrapped and lapped a minimum 300 mm around the pipe and step 'g'
is not required.

iv. earth filled excavations - unslotted pipes

a. place bedding sand or roadbase in the trench and compact as per the design

b. lay the pipe sections, one section at a time on top of the bedding

c. check and adjust the pipe level and grade if necessary. Adjust pipes by removal of
base material or ramming additional bedding under the pipe. Alternatively, slings may
be used around pipe ends.

d. place pits or sumps or both and remove knockouts

e. place side zone material and compact to the required relative density as shown on the
drawing

f. place a 150 mm maximum layer of material over the pipe and use a vibrating plate
compactor or similar to compact the fill to the required relative density. Repeat
backfilling and compaction until fill is at final level.

g. pack knockouts from the inside of the pits using sand or cement mortar (or geotextile if
detailed in this manner)

h. complete associated works (for example, pit lids or pots, ballasting, and so forth)

v. limited length due to outlet restrictions

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In some locations, a subsoil drain cannot be located deep enough to prevent it being
disturbed by track maintenance machines. In this case, the pipe may be wrapped in
geotextile, and then placed in the trench on a bed of aggregate to allow any adjustments to
the level and grade of the pipe to be made. The trench may then be filled with a suitable
pervious fill and compacted in layers.

vi. ash pockets

Where isolated pockets of ash are encountered, an impervious membrane may be placed
in the trench before the fabric is laid. This membrane should cover the ash pocket and
extend approximately 2 m either side of it. The rest of the drain is constructed as set out in
point 'i' above. This method is used only where the soil on either side of the ash pocket is
impervious; otherwise, the drain is constructed as per point 'ii' above. If an impervious
membrane is not available, the section of the drain above the ash pocket may be
constructed as for a drain in a pervious soil. See Figure 30 for the treatment of ash
pockets.

Figure 30 - Construction of a drain over an ash pocket

7.5.2. Lateral subsurface drain construction

This type of drain is commonly used to drain under turnouts and isolated water pockets in
embankments. For turnouts, the construction of lateral drains is the same as that for longitudinal
drains. The main difference is the depth of the pipe below rail level, which is a minimum of
1200 mm.

For embankment drainage, a lateral trench is excavated to the desired level, using a backhoe or
similar. Once the trench is excavated to the desired level, the base is graded to fall away from

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the embankment centre. The construction methods are the same as for longitudinal drains
(point 'iv' in Section 7.5.1).

7.5.3. Blanket drain construction

This type of drain is most commonly found at the base of embankments. Blanket drains are
usually constructed during embankment construction, embankment widening, or repairs to a
slip. The construction steps are as follows:

• excavate. For embankment widening or slip repair, steps should be cut into the existing
embankment (see TMC 411 Earthworks)

• level and compact the base with a fall away from the embankment centre

• lay out the geotextile. Any joints should have a minimum 1 m overlap.

• place aggregate, usually 20 mm to 53 mm aggregate up to 300 mm thick (this should be

laid and compacted in layers)

• fold sides of geotextile up over the top of the aggregate, then cover with a layer of
geofabric over the top of the aggregate

• place riprap (100 mm to 150 mm stone) over the exposed face of the drainage blanket as
protection

• build up the embankment to the desired level and compact in layers

7.5.4. Other types

Included in this section is the construction of horizontal and vertical drains. These drains are not
often used for track drainage and consequently will not be dealt with at this stage, with the
exception of the following.

The most commonly used vertical drain is used to drain water from behind retaining walls and
bridge abutments. This drain consists of a geotextile layer placed at the back of the wall and
connected to a pipe at the base of the wall.

Water reaching the geotextile can flow along the plain of the fabric that is down the back of the
wall, and is then removed by the pipe at the base. This may also be combined with horizontal
layers of geotextile to collect water seeping through the embankment or backfill behind the wall,
which is conducted towards the vertical drain, and then to the carrier pipe and removed.

This type of drain may be placed during construction and backfilling, or an area behind the wall
can be excavated for their installation.

7.5.5. Construction of an unslotted pipe drain

Follow the procedure as per step iv in Section 7.5.1.

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7.5.6. Sump installation

"Sumps shall be spaced at 30 m to 50 m centres, except through platforms where spacing shall
be 20 m to 30 m centres. Reduced centres may be applicable in the 6-foot between tracks to
account for track curvature."

At the location at which a sump is to be placed, the trench is widened and deepened to
accommodate for the sump. The base of the trench is then levelled and covered with a layer of
compacted sand or road base, which is a minimum 150 mm deep. This layer may be added to
so that the sump is positioned at the correct height.

Prior to placing the sump, the wafer of concrete covering the inlet and outlet is knocked out to
approximately the desired size. Drains using slotted pipes and geotextile are connected to
sumps as shown in Figure 31 below. Once the pipe is in place, any remaining gaps between the
pipe and the sump are grouted. The trench is then filled and compacted.

Figure 31 - Method of joining longitudinal subsoil drain to sumps

7.6. Other types of construction

Other construction methods that may be used include the following:

• pipe jacking

• tunnelling

• augering

• cast in place

These are seldom used for track drainage, and therefore are not covered in this document.

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7.7. Inlets and outlets

Some typical examples of inlet and outlet protection used are the following:

• precast concrete units

• grouted sand bags (Figure 21)

• concrete (Figure 22)

• reno mattresses and gabions (Figure 23)

• revetment mattress (Figure 24)

• spalls grouted or hand packed (Figure 25)

Inlet and outlet protection is to be installed as shown on the drawings and in accordance with
manufacturers’ instructions.

Typical details for a gabion headwall are shown in Figure 32.

Figure 32 - Gabion headwall – typical details

8. Maintenance of track drainage

Considerations for maintenance of track drainage include drainage principles, indications and
causes of ineffective drainage, typical problems and their solutions, and preparation for flooding.

8.1. General
Good track maintenance and effective track drainage are closely associated. The stability and
condition of the track and the formation is intimately related to the effectiveness of the drainage
systems.

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The track’s drainage system will be carefully maintained.

The consequences of poor or blocked drains can range from small areas of foul ballast to large
washaways or embankment failures.

Water needs to be drained away from the track as quickly as possible, so that it does not affect
the track stability.

Where sub-drainage work has been carried out, the outlets need to be kept clean to allow water
to run-off.

The cesses in cuttings need to be kept formed so that the water will run at the toe of the batter.
On banks, the cesses need to be graded away from the track.

Where bog holes exist, ample metal ballast should be kept on hand to replace the continued
loss of metal through fettling. The attention of the team manager needs to be drawn to this so
that they can have sub-drainage work carried out, when practicable.

Effective drainage is a major factor in minimising maintenance work necessary on welded track.

8.1.1. Drainage principles

Drains will do the following:

• Allow water to drain away. It is important that water be drained away from the track
structure as quickly as possible.

• Keep water flowing. If there are low spots in the drainage path, water will pond and will
saturate the sensitive track structure and weaken the material in that area.

• Control the path of water. Water should not be permitted to flow from the drain into areas
that will be damaged by water, for example, flowing into sinkholes or from the cess back
into the track because of debris in the cess.

• Control the flow rate of water. Water should not flow too slowly as to cause saturation
(ponding) or too rapidly as to cause erosion.

• Reduce erosion. Certain materials are prone to erosion and require additional treatment,
otherwise drains block rapidly, or slopes become undercut and cause instability.

• Keep water as far away as possible. Where the countryside is very flat and recommended
grades cannot be achieved, water should be drained away from areas that can be
damaged by saturation. For example, allow water to pond at the railway boundary rather
than the toe of the embankment.

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8.1.2. Indications of ineffective drainage

The following are indications of ineffective drainage:

• foul or dirty ballast

• pumping sleepers

• rotting sleepers

• bad top and line

• silted drains

• pumping joints and crossings

• pools of water

• broken or blocked pipes

If drainage is ineffective, then do the following:

• look for the cause

• fix the problem

Pools of stagnant water lying near the track will be drained and the problem that caused them
rectified. The proper action in this situation is to do the following:

• locate the problem

• drain the pools

• check all drains have proper cross-fall and grading

8.1.3. Possible causes of ineffective drainage

Possible causes of ineffective drainage are the following:

• broken pipes

• street gutters

• septic tanks

• unlawful diversion of water by property owners

To maintain good drainage the team leader needs to do the following:

• know where the drains are

• know which way they flow

• know where they discharge

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• clear any blockages immediately

• repair any weak spots

If team leaders cannot do the necessary work, they should do the following:

• report it to their team manager

• request extra staff, material, or equipment

Backhoes, bobcats, small bulldozers, and dumpers are some equipment that can be used to
clear drains.

8.2. Surface drainage

Maintenance operations carried out on surface drains usually fall into one, or a combination of
the following:

• weed control

• removal of debris from other track maintenance activities

• removal of sediment

• regrading

A build-up of weeds within the surface drain tends to slow the passage of water through the
drain, which, in turn, allows sediment to settle leading to a blockage of the drain. Such a
blockage can render a drain useless and lead to a decline in the effectiveness of other drains in
the system. For example, if a cut-off drain at the top of a cutting becomes blocked, water may
overflow the drain, run down the cutting face thereby increasing erosion of the face, and the
cess drain will eventually block up due to the additional sediment load.

Weeds may be removed using normal weed control practices.

Sleepers and rails, for example, left in the cess drains after maintenance work, tend to act as
dams allowing water to pond alongside the track and seep into the formation. This will also
allow sediment to settle. Therefore, old sleepers and rails should be removed to a suitable
dump at the completion of any track work.

When a drain fills with sediment, whether it is due to a blockage or a flat grade, this sediment
should be removed and the drain regraded if necessary. The type of equipment used to remove
the sediment depends on the extent of the blockage and the accessibility (equipment used may
range from a shovel to a gradall). Regrading is sometimes necessary due to scouring, or to
increase the grade of the drain slightly to reduce the amount of sediment that can settle in the
ditch (channel).

See Table 11 for a summary of surface drain maintenance.

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Where cutting faces are exposed, therefore undergoing unnecessary cutting face erosion
leading to an acceleration of sediment build-up in cesses, these cutting faces need to be
protected. Forms of protection commonly used are spray grasses, seeding, sodding, and
shotcrete.

Table 11 - Summary of maintenance of surface drains

Type of drain Problems encountered Possible remedies

Cess drain Blockages from weeds Poison.
Cess drain Blockages from old sleepers, Should be removed and cess
rail, and so forth regraded. Old sleepers and
rails should be removed when
replaced and not left lying in
the cess drain. If not removed
from site, sleepers should be
gathered up and disposed of.
Cess drain Blockages from other Approach other disciplines
discipline infrastructure about equipment relocation.
Cess drain Blockages from spillages and Remove and regrade cess.
spent ballast
Cess drain Silt build up, water ponding, Clean out cess drain and
and overflow as a result of regrade if necessary.
blockages
Cess drain Uneven grades Regrade cess.
Catch drain Same problems as above Same remedies as above.
Catch drain Animal (rabbit) burrows are Eradicate or remove animals
also a problem in some areas and fill in burrows.
Catch drain Poorly graded Regrade the drain.
Catch drain Scour - especially at outlets for Use more regular outlets,
catch drains above cuttings, thereby producing less water
where drains tend to be steep at lower velocities at each
thereby producing high outlet. Or regrade or line the
velocities drain or do both.
Mitre drain As above for cess drains. Regrade or line the drain. If
Greatest problem is scour necessary, provide some
means of retarding the flow
out of these drains.
Graded shoulder Water ponding Regrade the shoulders so that
they fall away from the track.

8.3. Subsurface drainage

Maintenance of subsurface drainage involves inspection, cleaning, unblocking, and repairing of
pipes, sumps, and outlets.

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8.3.1. Pipes and sumps

Pipes and sumps are susceptible to blockages due to ballast and rubbish from the track, tree
roots in search of water, siltation, and pipe breakages or crushing.

Sumps can be cleaned by digging the sediment, ballast, and rubbish out of the silt traps, or by
using a vacuum device (mainly used for deep sumps). Sumps filled with ballast are most
effectively cleaned using post-hole shovels, but these are ineffective for the removal of fine non-
cohesive silt. Square nose shovels of varying widths are suitable only where sediment fills the
silt trap. Where a sump is deeper than two metres, it becomes too difficult to clean using
shovels. In this case, a vacuum device may be used.

After the sumps have been cleaned, the adjoining pipes can be cleaned if necessary, by
rodding, hydroblasting, or similar.

Rodding of the pipes involves the pushing of a circular plug, of slightly less diameter than the
inside of the pipe, through the pipe using flexible rods. Rodding is done working from sump to
sump, starting at the downstream end. Any sediment or other debris pushed out of the pipe is
then cleaned out of the sumps.

Hydroblasting involves the removal of sediment by using a low-pressure, high volume water jet.
Low-pressure with high volume is used because high-pressure low volume water jets tend to
damage pipes. Hydroblasting is most effectively carried out using experienced contractors. The
process involved is as follows:

• sections of the pipe network are cleaned from sump to sump working from the outlet pipe

• various nozzles are used to break up any encrustations and remove debris. This is done by
either jetting it out into the sump or by relying on the volume of water and the grade of the
pipe to create a self-cleaning effect, and remove any sediment.

• after this operation is completed the sumps are cleaned either by the methods previously
mentioned or by sludge pumps

This process is then repeated in the next pair of sumps and so on.

Care needs to be taken to replace any displaced sump grates or covers removed during the
cleaning and inspection of the drainage system.

See Table 12 for a summary of subsurface drainage maintenance.

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Table 12 - Summary of maintenance of subsurface drains

Type of drain Problems encountered Possible remedies

Pipe, aggregate geotextile Blockages such as rubbish Clean out rubbish and ballast.
filter and sump type drain and ballast
(longitudinal drains)
Pipe, aggregate geotextile Silt Hydroblast or rod pipe.
filter and sump type drain Remove sludge with sludge
(longitudinal drains) pump or shovel.
Pipe, aggregate geotextile Scour outlet Provide scour protection or
filter and sump type drain decrease water velocity, or do
(longitudinal drains) both.
Sump grates and covers Blocked by rubbish and silt Remove cover or grate or
both, then clean sump if
necessary. Clean and replace
grates and cover. Remove
rubbish and so forth from site.
Aggregate and geotextile Blocked outlets Remove vegetation. Clean
drains such as blankets outlets. Ensure no water
ponds at outlets.
Outlets Scour Provide scour protection or
decrease water velocity, or do
both.
Outlets Blockages Clear away vegetation from
outlet. Clear any other debris
away from outlet, for
example, spent ballast and so
forth.

8.3.2. Outlets
Outlets are the most critical element of a subsurface drainage system because they are
susceptible to events that can impede the free flow of water. The main concerns are blockages
due to weed growth, siltation of the adjacent ditch or stream, debris from the track or slope, and
the activities of animals or humans. A system of marking outlets of subsurface drains should be
implemented to enable easy location of outlets.

TfNSW recommends that outlets and outlet markers be inspected and repaired, if necessary, as
part of routine maintenance at least once a year. As with the inspection of other drainage
system components, this should preferably be carried out in the period of least rainfall.

8.4. Typical problems and solutions

This section looks at typical drainage problems, suggests possible reasons for their occurrence,
and provides practical maintenance solutions that range from simple cleaning to upgrading
drainage.

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8.4.1. Cuttings
Drainage problems are exhibited by the following:

• water ponding

• poor track alignment and level through the cutting

• pumping of mud up through the ballast

• rock pumping

The main causes of these problems are the following:

• poorly graded cess drains

• blocked cess drains, that is, drains silted up due to cutting face erosion or debris (for
example, sleepers and spent ballast)

• foul ballast, that is, spillages from coal and wheat trains or mud causing the water to be
trapped in the ballast. Another possible cause is the damming of water caused by the
dumping of spoil by ballast cleaners at the ballast toe.

Another problem associated with cuttings is where cut-off drains have been provided but not
maintained. Therefore, water can pond within these drains, resulting in the saturation of the
cutting face which would lead to slipping, slumping, or piping of the cutting face. This may also
allow water to overflow the drains and run down the cutting face causing excessive cutting face
erosion, which in turn causes the cess drain to silt up quicker.

There are a number of solutions to these problems depending on the size of the cutting and the
number of tracks. These solutions are discussed in the following sections.

8.4.2. Narrow or steep cuttings

Depending on the severity of the problem, it may only be necessary to clean, regrade the cess,
and ballast clean the problem section.

The other alternative is to install subsoil drains. The cess is deepened and a subsoil drain
installed, and the ballast is then allowed to fall over the drain. Therefore, if the surface (cess)
drain becomes blocked (that is, silted up) the subsurface water is still being drained away from
the formation. This system can also be used on multiple track, provided the formation be in
good condition and graded towards the cess drains. Otherwise, the formation may need to be
reconstructed.

8.4.3. Wide cuttings

In wider cuttings or if widening of the cutting is possible, the cess drains need only be deepened
and widened so that water is drained out of and away from the track and does not prevent water
flowing away from the track.

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This method should be used where easy access is available, allowing regular maintenance to
be carried out.

Note: Cutting faces should be stabilised to reduce erosion and subsequent silting up
of cess drains. For example, spray grassing.

8.4.4. Embankments
The main drainage problems associated with embankments are water being trapped in the
ballast due to fouling of the ballast (either from spillages or mud), and the build-up of spoils from
previous ballast cleaning operations.

Another problem is that of water ponding at the embankment base, which may lead to slips.
This water may cause saturation of the embankment base consequently causing further
consolidation and settlement of the embankment.

To prevent water being trapped in the ballast, leading to formation failures, the shoulders of the
embankment need to be kept clean and graded away from the track. Therefore, windrows of
spent ballast cannot be allowed to build up on embankment shoulders. Depositing ballast
cleaning spoil over the side of the embankment stops water being trapped in the ballast but can
cause water to be trapped in the embankment itself. The spent ballast tends to form an
impermeable layer over the outside of the embankment.

Catch drains will be installed and maintained such that water is prevented from ponding at the
embankment base. An alternative to catch drains in flat areas is to grade surrounding ground
away from the embankment such that if water does pond in the area, it is away from the
embankment base.

At areas of heavy seepage through embankments, a transverse subsoil drain should be

installed to drain the water from the embankment, thereby reducing the possibility of
embankment saturation and any resulting problems.

On multiple tracks where drainage problems have been encountered it may be necessary to
install a transverse drain with suitable outlets to drain water effectively from the ballast.

Note: Embankment faces should be stabilised to reduce erosion problems (for

example, spray grassing, sodding, geotextile).

8.4.5. Soft spots or bog holes

Because this condition is often the result of water collecting in depressions in the formation, as
caused by inadequate or poorly maintained drains, the first consideration should be to upgrade
or clear existing drainage.

The provision of suitable drainage to preserve the stability of the formation is of prime
importance.

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The disposal of the impounded water from these depressions is achieved by excavating to the
lowest level and providing suitable permanent outlet drains.

Before deciding the actual method of treatment, the local conditions need to be investigated.
The objective of the investigation is to try to determine the source of the water and to obtain the
depth of the water pocket or depression.

To investigate a soft spot, trial holes are sunk at approximately 2 m intervals. This will determine
the depth of ballast and soft formation. This enables selection of the best type of drainage
system or solution to the problem.

The procedure to follow in the solution to the problem is as follows:

i. Determine the position and depth of the outlet drain or 'tap' drain by using trial holes to
locate the depth of ballast or the soft area.

ii. Excavate and remove the 'soft spot' and foul ballast. The lower level of the trench for any
sub drains used needs to be graded longitudinally at least 1:100 toward the outlet drain.
Sub drains should be lined or covered with a geotextile fabric and filled with clean new
ballast.

iii. Cess drains are also upgraded so that surface water will not penetrate the treated area
upon completion of the work. Where possible, they should be widened and graded
uniformly to the mouth of the cutting. This will help in allowing the water to run freely away.

iv. If the capping layer has been disturbed then it is then restored with crossfall angled
towards the drains.

v. The track is restored with 'clean' new ballast and resurfaced.

8.4.6. Scours and washaways

During heavy and prolonged rain, the normal drainage channels provided might not be able to
deal with the extra water flowing through them, with the result that flooding occurs.

In flat country, embankments may become submerged and saturated. If the water level rises
uniformly on both sides of the bank, there will not be a great amount of water flow. As a result,
little damage will occur. If, however, the flooding is confined to one side of the line, bridge and
culvert openings will be liable to scour. Should the water run over the top of the track, very
serious damage can result. The amount of damage will be dependent on the velocity or rate of
flow of the water. Any steps taken to reduce the velocity therefore will assist in reducing
damage.

The danger point is reached as water first commences to trickle over the formation. Scouring
then starts, first in the ballast and then in the formation. If there is a large difference in the water
levels on the two sides of the bank, the velocity will be high and damage extensive.

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During heavy flooding, washaways may be numerous. They may range from small sections of
ballast washed away to deep cuts where the whole embankment has been removed. The
method of doing temporary repairs will depend on the nature and size of the washaway and the
materials and equipment available.

If the ballast only is scoured out and it is not possible to get ballast to the site, quick repairs may
be made by redistributing the remaining ballast. This will lower the track into a long 'slack' and is
only a temporary measure to restore traffic. Repairs that are more permanent need to be
completed as soon as possible.

Where shallow scouring of the formation occurs, continuous sleeper pigsties may be used. For
deeper scouring, pigsties, trestles, and temporary beams will be required.

Permanent repairs will then require the closure of the track and reconstruction of the
embankment.

8.4.7. Slips
This type of earthwork failure comes within the experience of nearly every person associated
with track maintenance. Slips need not be large to cause serious damage and are very
dangerous in that they can occur suddenly and without warning.

It is desirable, in the initial construction of the track, to avoid unsuitable soils. However, track
staff are generally involved with tracks constructed for many years. As such, conditions need to
be dealt with as they are found.

Terracing and flattening of slopes will assist in bringing about stable conditions. Cuttings, in soft
material or in slopes liable to fail, may be widened to provide space for falling debris clear of the
track. Material removed from cuttings should not be placed on or pushed over embankment
sides without prior investigation of the embankment stability. Embankments can only be
widened using the correct procedures.

Advice on the appropriate batter slope, terraces, and procedures for the widening of
embankments should be sought from the Lead Civil Engineer, ASA.

Small slips may be foreseen and prevented by the removal of loose material or the building of
some form of protective structure. The removal of only the 'toe' of a slip will lead to increased
sliding. When it is necessary to clear the toe, only the minimum quantity to permit the passage
of trains should be removed. Mud flows, which result mainly from heavy rainfall, cannot always
be foreseen and prevented but continual maintenance of top drains will assist in reducing their
incidence.

Slips may be of several types or include features of each type.

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Flow movements
The soil material of a hillside or side slope may become so saturated with water that it moves
downward in the form of a mud flow. The rate of flow may be slow or rapid depending on the
degree of saturation and type of material. The slopes from which the flow starts need not be
steep if excess water is present.

The potential effect of this type of slip is to cover the track, push it out of line, or destroy any
form of support or retaining wall.

Shear failure
Sometimes an embankment or hillside is composed of soil without any great strength or
cohesion between its particles. It may be standing too steeply and cracks may develop which
will permit the entrance of water.

Movement of a large part of the slope takes place slowly at first, but can become very rapid as
complete failure takes place.

This type of slip may occur at any time, even many years after the railway is constructed. The
effect on the track is seen as a depression if the movement is minor or a total loss of support if
major movement occurs.

Slope adjustment
This is a natural occurrence due to erosion. Quantities of spoil or rock fall away from the sides
of cuttings and fall onto the track. They may be composed of fine material or rocks that are large
enough to derail trains.

Protection against the damage can be afforded by periodically removing any loose stones, and
by the provision of a wide bench at the toe of the cutting in which debris may collect clear of the
track.

8.4.8. Platforms
The main problem associated with platforms is the ponding of water that consequently causes
formation failures, exhibited as poor track alignment, pumping sleepers, and bog holes.

The solutions available depend upon the severity of the problem. The solutions include the
following:

• clean all sumps and pipes

• install a suitable drainage system in the 6-foot

• recondition track and install subsurface drainage system

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• completely excavate problem area and replace with densely compacted fill up to the next
formation level, then provide a 150 mm compacted granular capping layer and 300 mm of
ballast cover. During reconstruction, install a subsurface drainage system.

Also at stations with island platforms, there is often a problem with water ponding at the ends of
the platform. This can be remedied by placing a sump in the 6-foot connected to an existing
drainage system or suitable outlet.

Note: Run-off from station buildings and platforms can be piped into sumps. This
provides relatively clean water which can be used to help flush drainage systems.

8.4.9. Turnouts
With the increased axle loads and cyclic forces exerted on turnouts it takes very little water for
them to start pumping mud up through the ballast, consequently fouling the ballast and
compounding the problem.

Some solutions to this problem are as follows:

• Deepen and widen the cess drains on each side to drain water from the ballast and keep it
clear of the formation.

• Install subsurface drains under problem areas during turnout reconditioning or renewal.
Major problem areas are under heel blocks and crossings. These are points where the
most pounding (greatest impact load) tends to occur. Standard concessions to
T HR CI 12130 ST Track Drainage are required for subsurface drains within 10 m of a
turnout or crossing.

In some cases, during turnout and crossing renewals asphaltic concrete has been used as a
capping layer to help make the formation more impermeable, thereby giving it a longer life.

8.4.10. Yard drainage

The problems associated with yard drainage are similar to those of any other track work except
on a larger scale. On most lines, the drainage needs to cater for between one and four tracks,
but in yards there are usually many more. In addition, yards tend to be constructed on very flat
areas, so there is very little fall available for surface and subsurface drainage systems.

The simplest solution for any drainage problems in yards is to clean and regrade cesses and
provide regular outlets in the form of sumps, such that the best possible grades can be applied
to the surface drains.

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The most effective method is to have the formation graded as shown in Figure 33 below.

Figure 33 - Typical 'saw tooth' formation used in yards

Subsurface drains are located at the low points. If large flows are expected it may be necessary
to install carrier pipes. Carrier pipes may be placed at a deeper level thereby allowing the
grades of subsoil drains to be increased between sumps. Figure 34 shows a carrier pipe
arrangement.

Figure 34 - Carrier pipe arrangement

8.4.11. Bridge abutments and retaining walls

Unless adequate weep holes are installed during construction and kept clear by routine
maintenance, weep holes tend to block, trapping water behind the abutment or retaining wall.
This causes saturation of the earth (fill) behind the walls, which can lead to further consolidation
and settlement of the fill.

Weep holes are required at and above the capping layer level as well as at the base of a wall.
Weep holes should also be located at regular intervals down the wall, so if the bottom holes
become blocked the upper ones can still allow some water to escape.

Existing weep holes should be cleared during routine bridge maintenance. New holes should be
bored through the wall if no holes exist or the existing holes are inadequate, especially if there
are no weep holes present above the capping layer level.

8.5. Preparation for flooding

Preparation for flooding involves collecting historical data to assist with decisions, making
emergency plans, and issuing them to relevant staff.

8.5.1. General
Each Region is to have an emergency plan for dealing with major flooding that would affect train
operations.

Major flooding can occur with little warning and quick action may be necessary without time to
prepare.

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The 'flood plan' is to be documented and regularly updated. Copies are to be issued to each
team manager and other senior staff. In particular, a copy is to be part of the 'handover notes'
for relief officers.

The Regional staff should be the railway source for forecasting the effect of a flood on railway
facilities and be the adviser to Network Control. The civil maintenance engineer is to arrange
this service when a flood is forecast.

8.5.2. Historical information

The collection of data during flooding is most valuable in planning measures that will reduce or
avoid damage by future floods.

The heights of water levels at bridges, culverts, and on railway embankments should be marked
so that flood levels may be recorded.

At large bridges, the water level may be different at each end or on up and down stream sides.
Levels at all of these points should be recorded. Any appreciable difference in the up and down
stream flood levels at a bridge may indicate an inadequate waterway.

The records of previous floods in each river in the Region are to be kept up-to-date.

Frequency and severity of flooding are usually available on working plans and office files. Other
instructions require all flood heights to be recorded.

Local councils and other local bodies can provide a wealth of information on flood heights that
will allow upriver peak height information to be related to timing and severity of railway bridge
flooding levels.

Local papers and local residents can also advise on the time the river takes to rise, water
movements, and other essential local knowledge.

Bureau of Meteorology rainfall patterns assist in assessing run-off rates, saturation figures, as
well as river peaks and times.

From all available information a river flow chart should be prepared that will provide an accurate
forecast of the effect of future floods in the river systems on railway facilities once upriver
reports are received.

9. Documentation guide
The aim of this section is to provide a guide for external consultants in the preparation of design
drawings and hydrology reports for minor track drainage projects within the rail corridor. It also
covers external party development works discharging onto or through the rail corridor where this
has been approved by the concession process TS 10765 Concessions to ASA Requirements.

The requirements are also applicable to field staff doing track drainage design.

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This guide is provided to achieve standardisation of documentation associated with track

drainage design and external works discharging onto the rail corridor.

All documentation is to be retained on the project design file.

Minor drainage works within the railway corridor include open cess, pipes, pits, covers such as
lobster cages, and minor under track drainage openings.

9.1. Drawing guide

Typically, most rail drainage projects are site specific in that they have different site constraints,
varying terrain, and unique rainfall catchments. For this reason, TfNSW has not developed
standard drawings. However, it is fair to say that many details of track drainage remain generic.
The following aspects are considered the minimum requirements that should be detailed on
track drainage drawings.

9.1.1. General
For CAD drafting, refer to the documents TMD 0001 CAD and Drafting Manual - All Design
Areas – Sections 1 and 2, TMD 0001 CAD and Drafting Manual – Civil Design - Section 3, and
TMD 0001 CAD and Drafting Manual – Track Design - Section 7.

All drawings are to be completed using CAD (Microstation or AutoCAD). There is to be only one
drawing sheet per CAD file.

Drawings are to be detailed using standard TfNSW drawing sheets (A1 size). An electronic
template file of the standard TfNSW title block can be downloaded from ASA website.

Each drawing is to have a unique electronic document management system (EDMS) number.
These numbers can be requested from the TfNSW planroom.

Title blocks are to be filled out to the TfNSW requirements as detailed in TMD 0001.

9.1.2. Plan
Plan drawings require the following:

• drainage layout drawn at a minimum scale of 1:200 with Sydney shown on the left

• the layout will include identification or marking of drainage pits and sumps, for example pit
P1, P2, and so forth

• all railway tracks (including turnouts, crossovers, and sidings) to be shown and labelled, for
example, Main West - Down

• kilometrage marks to be shown along the track – say at 20 m centres. Text labelling at
even 100 m centres (20.100 km). Note that overhead wiring structure (OHWS) numbers
might not coincide with track kilometrage.

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• show the north point

• indicate and label railway boundary line

• show the top and bottom of cuttings, embankments, drainage channels, depressions, and
so forth

• show and label trackside furniture - if applicable (for example, signal footings, signal
troughing, air lines, train stops, services, face of platforms, retaining walls, bridge
abutments and piers, and so forth)

• show and label any applicable surveyed items (for example, trees, power poles, nearby
buildings, edge of roads or access roads, and so forth)

• show locations of any external services (as determined from a dial before you dig request-
submitted by the consultant)

• existing drainage to be indicated and labelled (dotted if they are to be removed)

• proposed drainage with dimensions of extent, pipe size or type or class. Arrows indicating
flow direction. Each pit to be labelled (for example, P1).

• extent of scour protection (dimensioned and labelled fully)

• pipe jacking - temporary excavation lines shown and pipe jacking direction indicated

• OHWS shown with footing outline and structure number indicated. Note that an OHWS
comprises a pedestal and either piled or spread footing base. Normally only the pedestal is
visible. TfNSW bridges and structures design personnel might be able to help determine
the footing size and type if a structure number is known.

The plan will be drawn from and based on a detail survey. However, at the discretion of TfNSW
(due to time or budgetary restraints), a schematic layout such as a 'track diagram' may be
inserted into the drawing. If a 'track diagram' is used, then the following note is to be included
alongside:

• This plan has been taken from track books and is not to scale.

• The effects of track curvature and clashes with existing OHWS footings or trackside
furniture are to be confirmed on site prior to ordering materials or construction or both.

• The possible effects of undermining of existing structures have been investigated and are
covered in the design.

9.1.3. Locality map

The following is required for locality maps:

• a street directory format showing the general area is to be included

• label “From Sydney” and “To Country” at the edge of the map

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• show north point

• circle and identify 'site of works'

9.1.4. Typical sections and cross-sections

The following is required for typical sections and cross-sections:

• drawn at a suitable and legible scale (usually 1:20 is adequate)

• show the track, ballast, and cross-fall of the track formation

• show nearest track and dimension the offset to the centreline of the drainage system

• dimension the depth below rail of the pipe system and the pipe cover to ground surface

• indicate width of trench, pipe type or size, geofabric type and fill and bedding material.
Dimension and label the compaction layers.

• if an open channel is adopted, fully dimension the channel and label any scour protection.
A table can be incorporated if the channel size varies along the length.

• if different methods of pipe installation are covered, then a typical section is required for
each method (for example, cess pipe installation different from undertrack pipe installation)

• cross-sections are typically required at all track crossings, adjacent to OHWS and where
there is a change in track configuration

9.1.5. Longitudinal sections (for pit or pipe and open channel)

The following is required for longitudinal sections:

• a separate longitudinal section is required along all pipe or drainage lines

• draw at a suitable scale (vertical exaggeration can be used to highlight grades)

• table along the bottom of the longitudinal section with headings indicating ‘Track km’,
‘design rail level (low rail)’, ‘cess level’ and ‘pipe invert level’

• indicate track kilometrage, rail levels, and cess levels at a minimum of 20 m centres and at
pit locations

• indicate pipe invert level at all pit locations

• indicate grade and extent of pipe runs and open channel

• all levels nominated need to be to Australian Height Datum (AHD). Where assumed level is
adopted, the assumed benchmark needs to be clearly identified.

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9.1.6. Additional details

Include any additional details that are essential for the construction of the project. These may be
individual details or separate drawings and may include items such as (but not limited to) the
following:

• how new pipes are to be joined in with existing drainage

• energy dissipating device details

• scour protection details

• pipe jacking collaring

• detention basin details

• lobster pot details

• temporary support of existing structures

9.1.7. Pit table

A pit table is to be included and will be set up in the format as shown in Table 13.

Table 13 - Pit table format

Pit no. Pit type Riser Top

P1 # 1/ 600 sq. x 1200 # 1/ 300 high riser 1/ 150 high LID.
deep (internal) # 1/ 150 high riser 1/ HD galv. cast iron
grate.
1/ ballast cage

# - designates step irons required in pit

9.1.8. Notes
Notes can include the following:

• design criteria (for example, design: average recurrence interval (ARI) of 50 years, loading:
pipes designed for 300 load allowance plus DLA train live load, and so forth)

• pipe or pit notes

• any other notes particular to the project (for example, shotcreting)

9.1.9. References (drawings)

The first drawing in the set is to reference all other drawings. The remaining drawings need to
refer to the first drawing and any other drawing that is referred to in the details on that sheet.

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9.1.10. Typical example drawings

Examples of typical drainage design drawings are in Appendix E.

9.2. External party development discharging onto or

through the rail corridor
The developer will provide the minimum supporting documentation as detailed in the sections
below. The requirements of TS 10765 also apply.

9.2.1. Hydrology and hydraulics report

A hydrology or hydraulics investigation report needs to be prepared by an AEO. The
investigation and analysis will include any possible impacts of any additional discharge
downstream or backwater effect upstream. This is to include discharge into council stormwater
systems.

The report will look at an average recurrence interval (ARI) of 50 years and should investigate a
range of storms from 5 minutes to 24 hour duration.

Note: TfNSW will accept reports done for ARI 100 years (as stipulated by some
councils) as long as the results satisfy TfNSW requirements.

It is TfNSW’s policy to reject any submission where the development will adversely affect
discharge rates onto or through the rail corridor. To control this, the developer may be required
to incorporate a retention and detention system within the developer’s property. Such a system
will be covered in the hydrology and hydraulics report. It will also be the consultant’s
responsibility to submit a ‘long-term maintenance management plan’.

It is TfNSW’s policy to reject any submission where the development will increase scouring
potential within the railway boundary. A drainage solution particular to the site may be required
to disperse flow effectively. Alternatively, provision of scour protection may be required.

Where the existing track drainage is found to be inadequate to accommodate the site discharge,
the developer will document the upgrade of the track drainage required at their costs. The costs
(to be borne by the developer) will include of upgrading of the TfNSW drainage system.

9.2.2. Drawings
Where upgrading of the TfNSW track drainage system is required, or additional drainage works
are required within the railway boundary, the documentation needs to be prepared in
accordance with Section 9.1.

Where the developer confines all drainage works to within their property, they need to supply a
layout plan that conveys the overall stormwater drainage system. This will include any pipes,
pits, basins, channels, and downpipes, and is to include the outline of the proposed dwelling

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and ground contour lines (including any ground level survey points taken). Any labelling of pipes
or pits or both will conform to the labelling conducted in the hydraulics and hydrology report. All
pipe inverts will be clearly identified in plan or on cross-sections. Any non-related information
will be filtered out.

For construction works carried out within the railway boundary, work-as-executed drawings are
to be submitted once works have been completed.

9.2.3. Long term maintenance management plan

Where a developer incorporates a detention and retention system to control discharge, then a
‘long term maintenance management plan’ will be required. This will detail the actions and
frequency of inspection and maintenance tasks to maintain the system effectively over its
design life.

Responsibility needs to be clearly defined in the maintenance plan. For example, the
maintenance plan needs to show who is responsible for the nominated inspection and who is
responsible for carrying out the maintenance tasks.

Any costs incurred by TfNSW as a direct consequence of failure of the stormwater system will
be passed onto the developer or owner.

9.2.4. Other considerations

The developer will seek the appropriate approval from the affected council or other relevant
authorities and parties.

The cost of design, documentation, and construction for any works within the railway boundary
will be borne by the developer. The developer will ensure that works are carried out in
accordance with railway safety requirements with appropriate TfNSW safety accreditation for all
workers.

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Appendix A Flow charts

Three flow charts are shown in this appendix. These are to illustrate the overall design process,
the surface drainage design process, and the subsurface drainage design process.

A.1. Flow chart 1 – overall design process

Figure 35 shows the generic design process applicable to all drainage systems.

Design investigation
1. Objective
2. Information required
3. Collection and study of existing information
4. Site investigation
5. Catchment estimation

Drainage system capacity

1. Recurrence interval
2. Design system

Rational method
Section 6.3.2

Peak surface runoff flow

Is the
drainage system required
a surface or subsurface
system?

Surface Subsurface

Flow chart 2 Flow chart 3

Produce any drawings and tables necessary for system

installation

Design stage complete proceed to construction phase

Figure 35 - Overall design process

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A.2. Flow chart 2 – surface drainage design

Figure 36 shows the design process specific to surface drainage.

From Section 6.4 calculate the peak flow rate QPF

Determine the local soil type such that the maximum

permissible velocity and roughness (Table 2, Table 3,
Table 4, Table 5, and Table 6) can be established.

Determine the slope from the preliminary investigation

survey (standard is 1 in 100).

Select trial channel size from Table 7.

Calculate the maximum flow rate for the selected trial

channel size (Q1)

yes Is Q1 ≈ QPF? no

Check the water velocity (V1)

Provide either a larger
channel or line the
drain
Is the
velocity less than the
no
maximum permissible
velocity? Table 8

yes

The channel size and water velocities are satisfactory

If new lining was chosen, then the cost of the lining

versus a larger unlined channel should be compared.

Figure 36 - Surface drainage design

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A.3. Flow chart 3 – subsurface drainage design

Figure 37 shows the design process specific to subsurface drainage.

From Section 6.5.1, calculate the peak surface runoff

(QR)

Carry out a hydrological study to establish QS or

Is QS = 0? no
estimate a value for QS

yes

Estimate the value of QC from the size of the upper drain

Is QC = 0? no
and approximately how full it flows

yes

QPF = QR + QS + QC (Equation 1)

Is the
subsurface drain a pipe or
pipe aggregate
aggregate
drain?

Determine the slope of the drain (standard is 1 in 100) Determine the slope of the drain

Size pipe for all pipe materials (min diameter 225 mm).
Select pipes from Table 9 such that max flow > QPF Select the size of the aggregate
determined from Equation 1

no
Is the
flow rate in the
pipe acceptable? Choose a value for K from Table 10

yes

Once the required flow is known, the drain area required

Calculate the strength of pipe required (Section 6.5.1)
can be calculated using Equation 8

Select other drainage components, for example, fabric

Compare the cost and availability of each type of pipe
and so forth (Section 6.1.2)

Draw up list detailing the items required and quantity

Select a pipe
and so forth.

Figure 37 - Subsurface drainage design

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Appendix B Drainage design checklist

The following checklist provides a useful guide for designing track drainage.

Drainage design and investigation checklist (Checklist D06)

Project identification

Location:
Line:
Details:
Project number or identification:
File:
Design delivery manager:
Target dates:

Delivery plan prepared: Yes No

Documentation: In-house External

Deliverable requirements

Hydrology and hydraulics report

Investigation report
Detailed design
Technical specification
Scope of works
Review of external design report

Prepared by:

Scope of work and project brief

What type of drainage is it? (i) track (ii) bridge – UB/culvert (i) (ii) (iii)
(iii) external party development
Has a scope of works been provided for Civil Works? Yes No
Has a project brief been provided? Yes No
Have the key design parameters been defined in the scope Yes No
or brief?
Are mandatory legislative or regulatory requirements defined Yes No N/A
in the scope or brief?

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Have any validation methods been established in the scope Yes No N/A
or brief?
Is a technical maintenance plan (TMP) required? Yes No N/A
Has functional and performance requirements been identified Yes No
by the client?
Have interface requirements been scoped (see below)? Yes No N/A
Are there any future proposals that have been identified (for Yes No
example, access road, embankment widening,
quadruplication, turnbacks, upgrades, track lifts, and so
forth)?
Do installation or maintenance manuals need to be Yes No
developed or changed?
Do you know the class of line? Yes No N/A
Do you know the speed? Yes No N/A
Do you know the maximum axle load? Yes No N/A
Do you know the operation (inspection and maintenance Yes No N/A
regime, and so forth)?
Do you know the usage factors such as numbers of trains? Yes No N/A
Will the configuration change affect the conditions of Yes No
operation?
Is training required prior to the installation of the design? Yes No
Have all the stakeholders (both internal and external) been Yes No
identified?

Discipline interface - track

Impact on track vertical and horizontal alignment (for Yes No

example, is there a need to lift or move the tracks)?
Are design track levels (low rail) known? Yes No

Discipline interface - geotechnical

Are founding parameters required for drainage design? Yes No

Are there any possible stability concerns with adjacent Yes No
structures or embankments?

Discipline interface - survey

Is a detailed survey scope required? Yes No

Is additional surveying required to define the catchment area Yes No
(for example, cross-sections, additional points)
Do existing drainage systems and services need to be Yes No
identified?

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Items required surveying (cross out or add as appropriate) – Yes No

existing drainage, pipe sizes, locations of pits, invert levels,
inlet and outlet , cess levels, rail levels, existing OHWS and
footings, visible services, banks, ballast edge, road edge,
site markers, survey pegs, fenceline, trees, surface levels,
define wingwalls, water level, local depressions, sketches

Discipline interface – electrical

Are there any Electrical requirements such as electrolysis, Yes No

transmission lines, and other services?

Discipline interface – services

Has TfNSW internal services searches been conducted? Yes No

Has ‘Dial Before You Dig’ external services searches been Yes No
carried out?
Does it look possible that conflict will exist with structure Yes No
footings

Discipline interface – external bodies

Have external hydrology reports been carried out in the area Yes No
(for example, local council and previous reports)?
Are external bodies required to be involved? Yes No
• local council Yes No
• RMS Yes No
• EPA Yes No
• water authorities Yes No
• land owner Yes No
• external development Yes No

Consultant:

Will any proposed configuration changes impact on TfNSW's Yes No

accreditation with Minister of Transport?
Will any proposed configuration changes require approval Yes No
from external bodies (EPA, RMS, water authorities, local
councils, and so forth)?

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Site data

Is the proposed works located in an (i) embankment, (ii) (i) (ii) (iii)
cutting, or (iii) open track
Project type: (i) renewal, (ii) refurbishment (UB and culvert), (i) (ii) (iii)
or (iii) upgrading for track drainage
Is there possible impact with existing structures – OHWS, Yes No
signal gantry, bridges, footings (for example, alignment
conflicts, undermining of footings, embankment stability
concerns)?
Site access – is there an existing access road? Yes No
Is there surrounding drainage systems? For example, local Yes No
council, RMS, private parties
Are there possible scouring concerns or evidence of site Yes No
scouring?
Are details (drawings) of existing drainage available? Yes No
Are there physical interfaces with other property owners or Yes No
Stakeholders?
• road crossings (including private crossings) Yes No
• interface between earthworks and other properties Yes No
• drainage flow to other properties Yes No
• installations such as pipelines laid within the corridor Yes No
• private sidings and bridges Yes No
• other statutory authority requirements for example, Yes No
environment?

Hazard and risk identification and analysis

Are there hazard sources from any of the following?

• normal operation Yes No
• environment Yes No
• equipment failure Yes No
• improper use or maintenance Yes No
Are there risks to any of the following?
• maintenance or construction staff Yes No
• public Yes No
• operators Yes No
• other equipment Yes No
• environment Yes No
Has the design and analysis considered the effect of
potential hazards and risks during the following?
• construction, including any temporary works required as Yes No N/A

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part of the project

• maintenance Yes No N/A
• operation Yes No N/A
• decommissioning and disposal Yes No N/A
Have possible mitigation measures been identified and Yes No N/A
documented?

Design and documentation checklist

Hydrology and hydraulics

Has proper hydrology and hydraulics calculations (including Yes No N/A

correct design parameters) been carried out by staff with the
proper engineering authority?
For complex hydrology studies – has an external service Yes No N/A
provider been nominated?

Hydrology report and investigations

Has the following information been documented:

• document control table (revision no, date, details, Yes No N/A
signatures)
• site description and background Yes No N/A
• options for refurbishment or renewal Yes No N/A
• catchment details Yes No N/A
• design methodology Yes No N/A
• hydrology parameters adopted Yes No N/A
• hydraulic parameters adopted Yes No N/A
• other design input (for example, survey, recorded Yes No N/A
flooding, measured values, consultation with councils or
authorities)
• analysis results Yes No N/A
• conclusions and recommendations Yes No N/A
• recommendation and concurrence by stakeholders Yes No N/A
Comments:

Detailed design drawings

Has the following information been documented:

• location and description and extent of the drainage Yes No N/A
works

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• drawing sheets and title block to TfNSW current Yes No N/A

standards
• plan view (Sydney on the left, layout of drainage, Yes No N/A
existing drainage, banks and depressions, all tracks
labelled, north point, boundary line, OHWS, services,
scour protection, flow direction, survey items, and so
forth)
• locality map Yes No N/A
• typical sections(offsets to rail, depth to rail, cover to Yes No N/A
pipe, trench details, compaction layers, geofabric, scour
protection, pipe labelled)
• longitudinal section along each pipe run (includes, track Yes No N/A
km, design low RL, cess level, pipe invert levels,
grades)
• relevant notes – design criteria, reference to appropriate Yes No N/A
standards and manufacturers.
• drawing references Yes No N/A
• additional details (join with existing, energy dissipaters, Yes No N/A
scour protection, pipe jacking, detention basin, lobster
pots, temporary support, and so forth)
• specific maintenance requirements, for example, Yes No N/A
retention basin – responsibilities and frequency of silt
removal
Do the design document and the information it contains Yes No N/A
comply with the standards?
Does the design reflect sound engineering practice? Yes No N/A
Have all known relevant project constraints have been Yes No N/A
considered?
Is this document fit for purpose? Yes No N/A
Is it suitable for construction use? Yes No N/A
Is it suitable for record (plan room) purposes? Yes No N/A
Does the design generally comply with the TfNSW track Yes No N/A
drainage guide?

Drawing check (reference – part 4.8 and 4.9 EM0323)

Accuracy - are dimensions correct? Yes No

Accuracy - is the drawing to scale? Yes No
Clarity - is the designer's intention clear? Yes No
Clarity - is sufficient information given? Yes No
Practicality - can the work be constructed as efficiently as Yes No
possible?
Consistency - is the drawing consistent with existing Yes No
drawings of the same type?
Regarding the question above - if not, can the change be Yes No N/A

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justified?
Standards - have relevant drafting standards and practices Yes No
been adhered to?
Standards - is the drawing presentation consistent with Yes No
TfNSW drafting standards?
References - are all the necessary cross-references Yes No
included?
Status - has the drawing status been updated? For example, Yes No
from tendering and construction
Title - is the drawing titled according to TfNSW practice? Yes No
Corrections - if corrections have already been marked on a Yes No N/A
previous check print held by the checker, are they included in
the current print?
Distribution - have the drawings been distributed to the Yes No
relevant stakeholders by the Design Delivery Manager
(DDM)?

Verification and approval

The drawing has been signed by the drafter, drawing Yes No

checker, and designer

Drafting checker

I certify that I have completed the drafting check.

Signature: Printed name: Date:

The drawings reflect the design intent, details, and Yes No

completeness.

Designer

I certify that I have completed all required actions.

Signature: Printed name: Date:

Have independent actions have been taken to verify the Yes No N/A
design as detailed on the drawings?

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Independent verifier

I certify that I have completed an independent design check.

Signature: Printed name: Date:

The design, drafting, and checking functions have been Yes No

carried out by people with appropriate engineering authority.
The design and drawing reflect sound engineering practice. Yes No
Reviews at progressive stages have been carried out with Yes No N/A
the client, to ensure that the design takes into account the
client’s needs, the functional requirements and constraints of
all relevant codes, standards, regulations, practices and
statutory requirements.
Comments:

The drawing is satisfactory for construction purposes. Yes No

The design phase for the discipline is complete. Yes No
Has the relevant information been entered in bridge Yes No
management system (DAD)?
TfNSW standards have been applied. Yes No

Approver

I certify that I have reviewed the design and have approved its issue.

Signature: Printed name: Date:

Accepted

I have accepted the design for use by TfNSW.

Signature: Printed name: Date:

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Appendix C Design investigation form

Date:

Design investigation - site investigation form.

(To be filled out during site investigation).

1. Location (that is, track region and kilometrage):

2. Track structure to be drained:

3. Condition of existing drainage system (if any):

4. Length of drainage system:

5. Restraints? Such as inlet and outlet, existing adjacent structures, track curvature, and so
forth:

6. Estimate catchment area:

7. Site access:

8. Any specific site safety requirements:

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9. Conduct services search. Any visible services noted:

10. Other comments:

11. Photographs: to be attached.

12. Site sketch:

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Appendix D Calculation of capacity required form

Calculation of capacity required form.

1. Location:

2. Average recurrence interval (ARI): ARI = 50 (All years

TfNSW
)
2
3. Size of catchment area acting at section under A = m
investigation:
2
Convert to = km
2 -6
km x10
4. Critical rainfall duration (tc)
Method 1: the normal procedure is to calculate
the equal area stream slope by graphing the
catchment elevation, drawing a line between the
start and finish of the catchment dividing equally
the area above and below the line. For ease of
calculations below it is assumed this is
equivalent to the catchment slope.
Mainstream length (L): L = Km
Change in height from start of catchment to h = m
point under consideration (h):
Catchment Slope (S) S =h/L = m/km
0.1 0.2
tc = 58 L / (A S ) from AR&R (2001) book 4 tc = min
equation 1.3
convert to = hrs
hrs (/60)
Method 2: using the basic formulae (for eastern
New South Wales).
0.38 2
tc = 0.76 A (where A=km ) from AR&R (2001) tc = hrs
book 4 equation 1.4
convert to = min
mins (x60)
5. Hydrology constants. These are looked up on
contour style maps from AR&R Volume 2.
2
Map 1.7 – 1 h duration, 2 year ARI i 1h = mm/h
2
Map 2.7 -12 h duration, 2 year ARI i 12h = mm/h
2
Map 3.7 – 72 h duration, 2 year ARI i 72h = mm/h
50
Map 4.7 – 1 h duration, 50 year ARI i 1h = mm/h
50
Map 5.7 – 12 h duration, 50 year ARI i 12h = mm/h
50
Map 6.7 – 72 h duration, 50 year ARI i 72h = mm/h
Map 7c – skewness factor G G =

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Map 8 – geographical factor F2 F2 =

Map 9 – geographical factor F50 F50 =
Figure 5.1 – Run-off coefficient for a 10 year ARI C10 =
2
Calculate 6 min duration, 2 year ARI. i 6min mm/h
From AR&R (2001) book 2 formulae B(3.1).
2 2 0.9
i6min = F2 ( i 1h )
50
Calculate 6 min duration, 50 year ARI. i 6min = mm/h
From AR&R (2001) book 2 formulae B(3.2).
50 50 0.6
i6min = F50 ( i 1h )
6. Determine the critical rainfall intensity Icr,50 for
the critical duration tc and an ARI of 50 years.
Method 1: Graphical method. Plot the points in
step 5 above on a Log-Pearson Type III
Interpolation diagram (see Diagram 2.2 in
AR&R) and join lines between these 2 year and
50 year ARIs. Refer to AR&R (2001) Volume
1,Book 2.
Method 2: Adopt AR&R formulas that interpolate
between rainfall durations. Determine modified
intensity values (I1h,50, I12h,50, I72h,50) using skew
lines at the bottom of the graph. Plot these
50
values as well as i6min on the duration
interpolation diagram 2.1 and read off the critical
50 year intensity, Icr,50. Refer to section A.3 of
AR&R (2001) book 2.
Method 3: Utilise computer software (for
example, “IFD” or “Drains”) by entering values
from step 5 above.
Icr,50 = mm/h
7. Determine the 50 year run-off co-efficient C50.
C10 - from step 5 above. C10 =
Geographical zone. From figure 1.2 AR&R zone = zone B
(2001) book 4. (for
Sydne
y
Metro
area)
Determine frequency factor (FF50). Using FF50 =
formulas or interpolating values given in table
1.1 of AR&R (2001) book 4.
Calculate C50 = C10 FF50 C50 =
8. Calculate the 50 year peak flow rate Q50 using
the Rational method. This represents the
amount of water that will flow on a catchment for
the critical 50 year storm.
Conversion factor for formulae F = 0.278
2
F = 0.278 if A is in km
3
Q50 = F C50 Icr,50 A Q50 = m /sec

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from AR&R (2001) book4 equation 1.1

9. Determine the required drain capacity
To calculate use figures 2.18, 2.19, 2.20, 2.21,
and equations 2.3, 2.4, 2.7, and 2.8 in AR&R
(1977).
3
QR = run-off quantity collected = Q50 QR = m /sec
3
QS = subsurface water intercepted QS = m /sec
3
QC = watering entering from another system (for QC m /sec
example, separate drainage line)
3
QPF = QR + QS + QC = QPF m /sec

Note: this procedure determines the amount of water passing at a single point based
on the original catchment area. If multiple catchment areas are incorporated into a
system, then this process should be repeated for each catchment.

Because of the repetitive and time-consuming nature of this procedure, it is

recommended that such method be entered into a spreadsheet, or computer program.
Alternatively, hydrology software incorporating AR&R methods may be a cost-effective
method to use in preference.

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Appendix E Drawings: typical examples

Typical examples of engineering drawings are shown in Figure 38 and Figure 39.

Figure 38 - Example drawing 1

Figure 39 - Example drawing 2

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Appendix F R loading configuration

The ‘R’ vehicle is a rigid truck with the same configuration as the prime mover portion (first three
axles) of the ‘T’ vehicle and the numerical portion is the vehicle’s weight in tonnes. The vehicle's
dimensions and axle loads are shown in Figure 40.

Figure 40 - Design vehicle configurations

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Appendix G Further reading

The following documents have not been directly referred to in this standard but are included
here as suggested reading. These documents may assist with providing important background
information on track drainage.

Australian standards

AS/NZS 2566.1 Buried flexible pipelines – Part 1: Structural design

AS 3572 Plastics - Glass filament reinforced plastics (GRP) – Methods of test

AS 4139 Fibre reinforced concrete pipes and fittings

AS 4678 Earth-retaining structures

Transport for NSW standards

ESC 240 Ballast

Transport for NSW drawings

CV 0517943 Single Pipe Headwall to Suit Pipes 225-600 mm Diameter

CV 0517944 Single Pipe Headwall to Suit Pipes 675-600 mm Diameter

CV 0517945 Twin Pipe Headwall (Splayed Wings) to Suit Pipes 225-600 mm Diameter

CV 0517946 Twin Pipe Headwall (Splayed Wings) to Suit Pipes 675-1800 mm Diameter

CV 0517947 Twin Pipe Headwall (Straight Wings) to Suit Pipes 225-600 mm Diameter

CV 0517948 Twin Pipe Headwall (Straight Wings) to Suit Pipes 675-1800 mm Diameter

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