SECTION 3

DRAINAGE WORKS

3.0 GENERAL

This work shall consist of the construction of surface drain, subsoil drains, pipe
culverts, box culverts, sumps and other drainage structures in accordance with
this Specification or as directed by the E. R. Drainage works shall be
constructed to the lines, levels, grades and cross-sections shown on the
Drawings or as directed by the E. R.

3.1 EXCAVATION AND BACKFILLING FOR DRAINAGE WORKS

3.1.1. Description

This work shall consist of excavation for the construction of surface drains, subsoil drains,
cast in situ box culverts, and other drainage structures, except pipe culverts, not
otherwise provided for in this Specification, and shall include furnishing, placing,
compacting and shaping foundation bedding materials, backfilling excavations against
completed structures with suitable material or granular backfill where specified, and the
removal and disposal of all excess excavated material, in accordance with this
Specification and as shown on the Drawings and as required by the E. R.

3.1.2. Materials

3.1.2.1. Excavation

Material excavated shall be classified as common excavation or rock as defined

in Section 1 of this Specification.

3.1.2.2. Granular Bedding Material

Granular bedding material for the foundations of structures shall be suitably

graded broken rubble, crushed gravel, sand or other material as specified on the
Drawings or as required by the E. R.

3.1.2.3. Concrete Bedding

Concrete bedding or blinding for the foundation of structures shall conform to the
requirements for the class of concrete specified on the Drawings or required by
the E. R.

3.1.2.4. Ordinary Backfill Material

Ordinary backfill material shall be suitable material as defined in Section 1 of this

Specification. The maximum particle size of the backfill material shall be 50 mm.

3.1.2.5. Granular Backfill Material

Granular backfill material shall be sand, crushed stone, crushed gravel or a

mixture of crushed and natural aggregates, shall be essentially free from
vegetative and other organic matter and clay, and shall not contain lateritic or
concretionary materials.

The material shall conform to the following physical and mechanical quality
requirements :-

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 i. the fines shall be non-plastic;
ii. sand shall have a gradation conforming to the envelope shown in Table
3.1 :

TABLE 3.1 - GRADING LIMITS FOR SAND BACKFILL

B.S. Sieve Size % Passing By Weight

10.0 mm 100
5.0 mm 90 - 100
1.18 mm 45 - 80
300 um 10 - 30
150 um 2 - 10

iii. material other than sand shall have a gradation conforming to one of the
envelope shown in Table 3.2

% Passing By Weight
B.S
Sieve Size
A B C

37.5 mm 100 - -
28.0 mm 70 - 100 100 -
20.2 mm 60 - 90 70 - 100 100
10.0 mm 45 - 75 45 - 75 -
5.0 mm 30 - 60 35 - 65 45 - 75
2.0 mm 20 - 50 25 - 50 30 - 60
425 um 10 - 30 10 - 30 15 - 35
75 um 0 - 2 0- 2 0 - 2

3.1.2.6. Concrete Backfill

Concrete backfill where specified shall be of the grade as shown on the Drawings
and shall conform to Section 9 of this Specification.

3.1.2.7. Excavation

The Contractor shall notify the E. R. sufficiently in advance of the beginning of

any excavation so that cross-section elevations and measurements may be taken
of the undisturbed ground. The natural ground adjacent to the structure shall not
be disturbed without permission of the E. R.

Trenches and foundation pits for structures and structure footings and
underdrains shall be excavated to the lines, grades and elevations shown on the
Drawings or as directed by the E. R. Excavations must be kept free from water
and temporary drains, sumps and pumps shall be provided when necessary. The
rate of excavation and backfill shall be approved by the E. R. The elevations of
the bottoms of footings shown on the Drawings are approximate only and the E.
R. may order in writing such changes in the dimensions or elevations of footings
as may be deemed necessary to secure a satisfactory foundation.

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 Boulders, logs and other objectionable materials encountered in excavation shall
be removed.

After each excavation is completed the Contractor shall notify the E. R. to that
effect and no footing, bedding material or structure shall be placed until the E. R.
has approved the depth of excavation and the character of the foundation
material.

Rock and other hard foundation material shall be cleared of all loose material and
cut to a firm surface, either level or stepped or serrated, as specified or shown on
the Drawings or directed by the E. R. All seems and crevices shall be cleared out
and grouted with Portland cement grout at the time the footing is placed.

All loose and disintegrated rock and thin strata shall be removed. When the
footing is to rest on material other than rock, special care shall be taken not to
disturb the bottom of the excavation, the excavation to final grade shall be
deferred until just before the footing is to be placed. When, in the opinion of the
E. R., the foundation material is soft or mucky or otherwise unsuitable, the
Contractor shall remove the unsuitable material and insert foundation fill material
or concrete as specified or shown on the Drawings or directed by the E. R. If
foundation fill material is required it shall be placed and compacted in layers not
more than 150 mm thick or as directed by the E. R. The degree of compaction
shall be equivalent to that of the surrounding foundations.

All excavation surfaces and surfaces of backfill material against which concrete is
to be placed shall be even and firm and true to line and level.

All excavated material, so far as suitable, shall be utilized as backfill or

embankment. The surplus material, whether or not temporarily allowed to be
placed within a stream area, shall be finally disposed of in such a manner as not
to obstruct the stream nor otherwise impair the efficiency or appearance of the
works, nor is it to endanger the partly finished structure.

Excavated material suitable for use as backfill may be deposited by the

Contractor in storage piles at points convenient for rehandling of the material
during the backfilling operation.

Excavated material shall be deposited in such places and in such manner as not
to cause damage to highway, services or property either within or outside the
road reserve, and so as to cause no impediment to the drainage of the Site or
surrounding area.

3.1.3. Backfilling With Ordinary Or Granular Backfill Material

All spaces excavated under this Specification and not occupied by a permanent
structure shall be backfilled. Backfill material shall be free from large lumps, wood
and other extraneous material.

Backfill not within the embankment areas shall be placed in layers not more than
250 mm in depth (compacted measurement) and shall be compacted to a density
comparable with the adjacent undisturbed material.

Backfill within the embankment areas shall be made with approved material
placed in uniform layers not to exceed 150 mm in depth (compacted
measurement) and each layer shall be constructed in accordance with Section 2
of this Specification except that mechanical tampers may be used for
compaction. Each layer of backfill shall be wetted uniformly as necessary and
compacted to the same requirements as the adjacent earthwork as specified in

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 Earthworks Specification. Unless otherwise approved by the E. R., hand tamping
will not be accepted.

In placing backfill and embankment, the material shall be placed insofar as

possible to approximately the same height on both sides of the structure. If
conditions require backfilling appreciably higher on one side, the additional
material on the higher side shall not be placed until permission is given by the E.
R. or until the E. R. is satisfied that the structure has enough strength to
withstand any pressure created.

Backfill for embankment shall not be placed behind the walls of box culverts until
the top slab is placed for the required time and not less than three days. Backfill
and embankment behind abutments held at the top by superstructure shall be
carried up simultaneously behind opposite abutments and side walls.

No backfilling shall be placed against any structure until permission shall have
been given by the E. R. Jetting of fill or other hydraulic methods involving, or
likely to involve, liquid or semi-liquid pressure shall be prohibited.

Special care shall be taken to prevent any unduly high pressures against the
structures.

The placing of embankment and the benching of slopes shall continue in such a
manner that at all times there will be a horizontal berm of thoroughly compacted
material for a distance at least equal to the height of the abutment or wall to be
backfilled.

3.2 CHANNEL EXCAVATION

3.2.1. Description

This work shall consist of excavation for waterway channels both inside and
outside the road reserve as shown on the Drawings or directed by the E. R., and
shall include all required excavation for widening, training or permanently
diverting rivers, streams and irrigation and drainage channels other than drains
and ditches appurtenant to the roadway, except excavation of topsoil for use in
the Works and excavation required for clearing and grubbing. This work shall
also include the backfilling of old channels, haulage to their points of utilization in
the Works or the removal and disposal of all excavated materials, the
construction of appurtenant bunds, dikes and berms, and the shaping and
finishing of all earthworks involved in the construction of channels in accordance
with the required lines, levels, grades and cross-section.

3.2.2. Materials

Channel excavation shall be classified as common excavation or rock as

specified in Section 1.

3.2.3. Construction Methods

All suitable materials removed from channel excavations shall be used for
backfilling waterways to be abandoned and constructing bunds, dikes and other
earth appurtenances as required. Surplus suitable materials shall be used as far
as is practicable in constructing the roadway. The Contractor shall provide
borrow of satisfactory quality and approved by the E. R. should this be necessary
to complete the work. Borrow which is required to replace suitable excavated
materials needed for construction which the Contractor elects to waste shall not
be paid for.

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 Excavated unsuitable material, suitable material surplus to that needed for
construction and suitable material that the Contractor elects to waste, shall be
disposed of at designated areas in such a manner as to present a neat
appearance and not obstruct flow in any channels, ditches or drains, nor cause
damage to highway works or property, all to the satisfaction of the E. R.

During construction, channel excavations shall be kept drained as far as is

practicable and the work shall be carried out in a neat and workmanlike manner.

All channels and appurtenances shall be excavated and constructed to the lines,
levels, grades and cross-sections shown on the Drawings or as directed by the E.
R. Excavation beyond the limits required shall not be paid for and shall be
backfilled at the Contractor’s expense as directed by the E. R. should be deem if
necessary.

Sections of channel abandoned owing to diversions shall be backfilled as directed

by the E. R.

3.3 SURFACE DRAINAGE

3.3.1. Surface Drainage Types

Surface drains of the types shown on the Drawings shall be constructed to the
lines, levels, grades and cross-sections as specified or as directed by the E. R.
Surface drains shall include interceptor drains, embankment toe drains, shoulder
drains, bench drains, berm drains, median drains, outfall drains, cascade drains,
etc.

Any of the above drains may be constructed either unlined or lined using cast in
situ concrete, precast or porous concrete drain sections, or stone pitching.

3.3.2. Surface Drain Construction

3.3.2.1. Unlined Drains

Excavation for unlined drains shall be trimmed to form a smooth, firm surface to
the required lines, levels, grades and cross-sections as shown on the Drawings
or as required by the E. R.

Any areas of over excavation shall be made good to the satisfaction of the E. R.,
all at the Contractor’s expense.

3.3.2.2. Cast In Situ Concrete Drains

Excavation shall be carried out to the lines and levels as specified and as shown
on the Drawings. Templates which may be of timber or steel shall then be
provided to ensure the thickness and shape of the concrete drains. The concrete
shall be poured in sections not exceeding 2m in length and shall be carried out
between end forms in alternate bays. Construction joints shall not be formed in
the inverts.

All concrete shall be grade 20/20 concrete unless otherwise specified and shall
conform to the requirements of Concrete Specification. Weep holes shall be cast
in situ as shown on the Drawings or as directed by the E. R.

3.3.2.3. Precast Concrete Drain Sections

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 Precast concrete block inverts shall be of the shapes and dimensions as shown
on the Drawings and shall be of grade 20/20 concrete conforming to the
requirements of Concrete Specification or of porous concrete unless otherwise
specified. The precast concrete drain sections shall be manufactured using good
quality moulds and the finished product shall be round and have smooth inside
surfaces all to the approval of the E. R. Ready made precast concrete drain
sections may be used subject to the approval of the E. R. Samples of ready
made drain sections shall be submitted to the E. R. for his approval before
placing of orders. Notwithsanding any approval given by the E. R., any defective
or broken drain section shall be replaced by the Contractor at his own expense
before or after laying in position.

Precast concrete drain sections shall be laid on concrete bedding in trenches

excavated to the lines and levels as specified and jointed to produce a neat even
alignment and gradient. The joint shall be grouted with 1:3 cement mortar
complying with Sub-Section -5.2.2 and weep holes shall be provided as shown
on the Drawings or as directed by the E. R.

Porous concrete shall comply with the requirements of porous concrete for pipes
as described in M.S. 525. Cement and aggregates used in the manufacture of
the porous concrete drain sections shall conform to the requirements of Concrete
of this Specifications.

Mass concrete for bases shall be of grade 10/25 concrete or as specified and to
the dimensions and thicknesses as shown on the Drawings.

3.4 STONE PITCHING

3.4.1. Description

This work shall consist of the construction of all structures or parts of structures
to be composed of stone pitching either grouted or ungrouted as shown on the
Drawings or as directed by the E. R. including erosion protection pavements and
aprons, drain linings, culvert inlets and outlets, etc. The work shall be carried out
all in accordance with this Specification and to the lines, levels, grades,
dimensions and cross-sections shown on the Drawings and as required by the E.
R.

3.4.2. Materials

3.4.2.1. Stone

Stone shall be clean rough quarry stone, or pit or river cobbles, or a mixture of
any of these materials, and shall be essentially free from dust, clay, vegetative
matter and other deleterious materials. Individual pieces of stone shall be
approximately cubical of spherical and shall have least dimensions in the range
100 to 150 mm and a maximum dimension of 250 mm, maximum, unless
otherwise specified. The stone shall be hard, tough, durable and dense, resistant
to the action of air and water, and suitable in all respects for the purpose
intended.

3.4.2.2. Cement Mortar

Cement mortar, unless otherwise specified, shall contain 1 part ordinary Portland
cement to 3 parts fine aggregate by volume. Water shall be added to the mix to
produce a suitable consistency for the intended use, all to the satisfaction of the
E. R. The constituent materials of the mortar shall comply with the appropriate
requirements of Concrete Specification.

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 The ingredients for mortar shall be measured in proper gauge boxes and mixed
on a clean boarded platform or in an approved mechanical batch mixer.

All mortar shall be used within 30 minutes of mixing and no reworking of mortar
shall be permitted thereafter.

3.4.3. Construction Methods

3.4.2.1. Grouted Stone Pitching

Prior to constructing grouted stone pitching, the surfaces against which it is to be

placed shall have been finished in accordance with the appropriate provisions of
this Specification. Notwithstanding any earlier approval of these finished
surfaces, any damage to or deterioration of them shall be made good to the
satisfaction of the E. R. before grouted stone pitching is placed.

Construction of grouted stone pitching shall commence at the lowest part of each
structure or section of a structure and continue progressively upward. Long
structures such as drain linings and slope protection pavements shall be
constructed in sections of practicable length, to the satisfaction of the E. R. The
surface against which the work is to be placed shall be moistened with clean
water a little in advance of construction, and covered with a layer of cement
mortar about 50 mm thick. Stones shall than be firmly set by hand into the
mortar, densely packed against adjacent stones and built up to form a stone
structure of more or less uniform thickness which shall nowhere be less than 150
mm (measured perpendicularly to the surface covered). All the while that stones
are being placed, all voids in the structure shall be packed solidly with mortar and
stone spalls ; however the surfaces of stones in the exposed faces and edges
shall not be covered with mortar. The exposed surfaces and edges of the
structure shall be constructed such that they have as large a proportion as
practicable composed of stone faces. Weep holes shall be provided as shown on
the Drawings or as directed by the E. R.

Mortar which has been mixed for more than 30 minutes shall not be used in the
works. Nor shall mortar be laid against the supporting surface more than 2
minutes before pitching stone and building up the structure to full thickness is
commenced on any section of the work, as the construction advances.

The work shall be carried out and finished all to the satisfaction of the E. R.

3.4.2.2. Ungrouted Stone Pitching

Where shown on the Drawings, ungrouted stone pitching shall be hand set to
provide maximum interlocking effects. The stones, the largest of which shall be
used at the bottom, shall be well bedded on a 75 mm layer of gravel or aggregate
rammed to an even surface. The whole work shall be finished to the satisfaction
of the E. R.

3.5 GABIONS

3.5.1 Description

This work shall consist of the construction of miscellaneous erosion protection

and retaining structures to be composed of stone filled wire mesh gabions. The
work shall be carried out all in accordance with this Specification and as shown
on the drawings and/or as approved by the E. R.

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3.5.2 Materials

3.5.2.1. Wire Mesh Gabions

Gabions shall be rectangular baskets of the required dimensions as shown on the

drawings or ordered by the E. R. Unless otherwise specified, they shall be of the
following standard dimensions :-

i. width - 1.00 metre;

ii. length - 1.00, 2.00 or 3.00 metres;

iii. height - 0.50 or 1.00 metre.

Gabions longer than 1.00 m shall be divided into compartments of equal length
not exceeding 1.00 m by wire mesh diaphragms securely tied along all edges.
Each gabions or compartment of a gabion shall be provided with at least 4 cross-
connecting wires if its height is 0.50 m or less, and with at least 8 cross-
connecting wires if its height is in the range 0.50 to 1.00 metre.

Gabions shall be fabricated from steel wire manufactured in accordance with B.S.
1052 and galvanised in accordance with M.S. 407, or such similar standards as
the E. R. shall approve. The galvanized wire sizes used shall be in accordance
with Table 3.3

TABLE 3.3 - GALVANISED WIRE SIZES OR GABIONS

Type of Wire Minimum Diameter

Selvage (perimeter) wire 3.50 mm

Mesh wire 2.70 mm

Tying and connecting wire 2.20 mm

Gabion mesh shall be triple twisted and shall have a uniform hexagonal pattern
with openings of 100 x 200 mm or less. The mesh shall be securely tied to
selvage wires to form rectangular panels which shall be securely wired together
to form the completed gabion baskets. The ties and connections for each gabion
basket shall comprise not less than 8% of its total weight, and the fabrication
shall be all to the satisfaction of the E. R.

3.5.2.2. Polyvinyl Chloride Coating

When specified on the Drawings, all wire used in the fabrication of gabions and in
the wiring operation during construction shall, after galvanizing, have extruded on
to it a coating of polyvinyl chloride (PVC). The PVC coating, not inclusive of
galvanizing, shall nowhere be less than 0.55 mm in thickness.

3.5.2.3. Stone

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 Stone fill for gabion shall be clean rough quarry stone, or pit or river cobbles, or a
mixture of any of these materials, and shall be essentially free from dust, clay,
vegetative matter and other deleterious materials. Individual pieces of stone shall
have least dimensions not less than 20 mm larger than the gabion mesh
openings and greatest dimensions not more than 250 mm. The stone shall be
hard, tough, durable and dense, resistant to the action of air and water, and
suitable in all aspects for the purpose intended. The material shall be approved
by the E. R.

3.5.2.4. Construction Methods

Prior to placing gabions, the surface on and against which they are to be
constructed shall have been prepared and finished in accordance with the
relevant provisions of the appropriate Sections of this Specification.
Notwithstanding any earlier approval of these finished surfaces, any damage to
or deterioration of them shall be made good to the satisfaction of the E. R. before
gabions are placed.

Each gabion basket shall be put in place in its turn, completely fabricated except
for the fastening down of the lid, stretched to the correct shape and dimensions,
and fastened securely to all contiguous baskets along each edge with tying wire.
The basket shall then be tightly packed with approved stone by hand in such a
manner that voids are kept to a practicable minimum and are uniformly
distributed in the stone mass. Finally, the lid of the basket shall be securely
fastened down with tying wire along all hitherto unfastened edges, all to the
satisfaction of the E. R. In no case shall the weight of the finished gabion be less
than 1300 kg per cubic metre.

As a gabion structure is built up, backfilling against finished gabions shall be

carried out as necessary for proper progressive construction, all in accordance
with the relevant provisions of the appropriate Sections of this Specification.
Unless otherwise specified, vertical joints between gabions shall be staggered in
gabion structures in a pattern similar to the joints in running bond brickwork.

3.6 BRICKWORK

3.6.1 Description

This work shall include the laying of brickwork to the lines, levels and grades shown on
the Drawings and/or as directed by the E. R.

3.6.2 Materials

3.6.2.1. Common Bricks

Common bricks shall be sound, hard, well burnt, of proper size and clean and
shall give a clear ring when struck. They shall be Class 3 standard format
complying with the requirements of M.S. 76. Bricks shall be obtained from
manufacturers approved by the E. R.

3.6.2.2. Cement Mortar

Cement mortar for brickwork shall comply with the requirements of Sub-Section
5.2.2

3.6.3 Construction Methods

3.6.2.3. Brick Laying

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 Brickwork shall be executed with cement mortar and shall be of the thickness and
bonds as shown on the Drawings. Bricks shall be kept damp until used and shall
be laid on a full bed of mortar. The brickwork shall be true to line and plumb, and
courses shall be kept truly level. The thickness of mortar joints shall not exceed
10 mm and shall be such that 4 courses of brickwork forms a height of 300 mm.
Newly laid brickwork shall be protected from the harmful effects of sunshine, rain,
running and surface water and shocks. Any brickwork that is damaged shall be
taken down and rebuilt and the joints raked out and pointed as directed by the E.
R. Any such remedial work shall be at the Contractor’s own expense.

3.6.2.4. Plastering Brickwork

All exposed brickwork surfaces shall be plastered. The plaster shall be applied in
2 coats generally to a total thickness of 20 mm and shall be finished with a steel
trowel for internal surfaces and with a wooden float for external surfaces.

Plain plaster shall consist of 1 part masonry cement complying with M.S. 794 to 3
parts of sand by volume. Where ordinary Portland cement is used, plasticiser of a
type approved by the E. R., may be added to the mix in accordance with the
manufacturer’s instructions.

Ordinary Portland cement and water shall comply with the appropriate
requirements of section 2 of this Specification.

Weep holes shall be provided as shown on the Drawings or as directed by the E.

R.

3.7 SUBSOIL DRAINS

3.7.1 Description

This work shall include the supply and installation of subsoil drains constructed in
accordance with this Specification at the locations and in accordance with the
lines, levels and grades as shown on the Drawings and/or as directed by the E.
R.

3.7.2 Materials

3.7.2.1. Pipes

Porous concrete pipes for subsoil drains shall comply with M.S. 525.

Clay pipes for subsoil drains shall comply with B.S. 1196.

Polyvinyl Chloride (PVC) pipes for subsoil drains shall consist of hard, clean and
sand conforming to the grading limits given in Table 3.4. The material passing the
425 um sieve shall be non-plastic when tested in accordance with B.S. 1377.

3.7.2.2. Filter Material

Filter material used in the construction of subsoil drains shall consist of hard,
clean sand conforming to the grading limits given in Table 4.0 The material
passing the 425 um sieve shall be non-plastic when tested in accordance with
B.S. 1377.

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 TABLE 3.4 - GRADING LIMITS FOR FILTER MATERIAL

B.S. Sieve Size % Passing By Weight

10.0 mm 100
5.0 mm 90 - 100
2.36 mm 75 - 100
1.18 mm 55 - 90
600 mm 35 - 59
300 mm 8 - 30
150 mm 0 - 10

3.7.2.3. Filter Cloth

The synthetic filter cloth shall be a non-woven type of approved manufacture

having the following properties :-

(a) Chemical Composition Requirements

Fibres used in the manufacture of the engineering fabric shall consist of a long
chain synthetic polymer, composed of at least 85% by weight of polypropylene,-
ethylene, -esteramide or -vinylidene chloride and shall contain stabilizers and/or
inhibitors added to the base plastic (as necessary) to make the fabric resistant to
deterioration from ultraviolet and heat exposure.

(b) Physical Property Requirements

The physical properties of the filter cloth shall comply with Table 3.5

TABLE 3.5 - PHYSICAL PROPERTY REQUIREMENTS FOR FILTER CLOTH

Grab Strength 0.9 kN

(ASTM D1682)

Puncture Strength 0.4 kN

(ASTM D3787 - 80a)

Burst Strength 2100 kN/sq.m

(ASTM D3786 - 80a)

(c) Filtration Requirement

Equivalent opening size of the filter cloth determined by sieving as described in

ASTM D422 shall be less than the eighty-five percentage size of the adjacent
soil.

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 (d) Permeability Requirement

The equivalent Darcy Permeability of the filter cloth shall be greater than 10 times
the Darcy Permeability of the soil to be drained.

3.7.2.4. Cement Mortar

1:3 cement mortar for use in pipe joints shall comply with Section 9.

3.7.3 Construction Methods

Excavation for subsoil drains shall be carried out all in accordance with
Earthworks Specifications.

Filter material as described in Sub-Section 8.2.2 above shall be placed and

uniformly compacted by a suitable method approved by the E. R. to form a firm,
even bedding for the pipe drain as shown on the Drawings.

The pipe sections shall be set firmly against the filter material bedding with the
flow lines in the design position. For pipes with mating joints, the receiving ends
shall be upgrade, and the pipe joints shall be fully mated. For butt jointed pipes
with collars, the pipe sections shall be fully contiguous, and the collars properly
centred over the joints.

Joints shall be spot mortared as necessary to hold the pipe sections correctly
centred and aligned, but not so as to unduly restrict the infiltration of water
through the joints.

Slotted or perforated pipes shall be tightly wrapped in filter cloth such that the
entire length of the mortared pipe is covered by at least 2 layers of cloth. All joints
in both layers shall have an overlap of at least 100 mm and joints in the outer
layer shall be offset by at least 300 mm from joints in the inner, all to the
satisfaction of the E. R.

After pipe laying and, if appropriate, wrapping has been approved by the E. R.,
the remainder of the filter material shall be placed and uniformly compacted by a
suitable method approved by the E. R. to form a dense, even surround to the
pipe as shown on the Drawings. Care shall be taken that the pipe is neither
damaged nor displaced.

Backfill shall then be placed and compacted in accordance with the appropriate
provisions of Sub-Section 2.4.

3.8 R.C. PIPE CULVERTS

3.8.1 Description

This work shall comprise the supply and installation of reinforced concrete pipe
culverts, inclusive of excavation, backfilling, jointing, bedding, construction of
headwalls, wingwalls, aprons and sumps and channel protection works, all in
accordance with this Specification and the details shown on the Drawings.

3.8.2 Materials

3.6.2.1. Pipes

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 Reinforced concrete pipes shall conform to the requirements of M.S. 881 and
shall be supplied by manufacturers approved by the E. R.

Rebated pipes of diameter 600 mm and above shall be internally rebated.

Collars shall be precast with grade 25 concrete and shall be suitably reinforced
all in accordance with Concrete Specification. The width of the collar shall be not
less than 150 mm and the minimum thickness shall be 50 mm.

Rubber rings for spigot and socket pipes shall comply with the requirements of
Type 2 as specified in B.S. 2494.

3.6.2.2. Cement Mortar

1:3 cement mortar for jointing of reinforced concrete pipes shall conform to the
requirements of Section 9.

3.6.2.3. Bedding Material

The type A bedding shall consist of Grade 20/20 concrete reinforced with a layer
of wire mesh no. A8 as shown in drawings.

Type B bedding shall consist of clean natural sand or gravel sand of suitable
gradatiobn and quality, approved by the E. R. The material shall have a
maximum particle size of not more than 12 mm.

3.8.3 Excavation and Backfilling for R.C. Pipe Culverts

3.8.3.1. Excavation

(a) General

Unless otherwise directed by the E. R., prior to construction of a pipe culvert, the
earthwork at the required location shall have been constructed to a level at least
600 mm above the top of culvert design levels or to the top of subgrade levels,
whichever is lower.

Pipe culverts specified to be constructed in trench conditions shall be excavated

in accordance with Sub-Section 3.8.3.1 (b) below.

Where drainage conditions or other circumstances so require, the E. R. may

direct the Contractor to construct the pipe culvert without first constructing the
earthwork to the level specified above, in which case excavation and foundation
preparation shall be in accordance to below.

(b) Trench Method

The trench to receive a culvert pipe shall be of sufficient width and depth to
enable the placing of bedding material and construction of pipe joints in
accordance with this Specification, and bottom of the trench shall be trimmed to a
suitably smooth plane surface which shall be kept free from water, all to the
satisfaction of the E. R. Where rock or other hard unyielding foundation material
is encountered in the trench, it shall be excavated to a depth below the bottom of
pipe design levels of at least 300 mm or 12.5 mm per 300 mm of fill to be placed
over the top of the pipe, whichever is greater up to a maximum of 75% of the
internal diameter of the pipe. The hard material so excavated shall be replaced
with suitable material uniformly compacted in layers of not more than 150 mm
compacted thickness to provide satisfactory support for the pipe, all to the
satisfaction of the E. R.

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 (c) Open Ground Method

Where existing ground levels are above top of bedding material design levels and
firm foundation materials are encountered, excavation and foundation preparation
shall be similar to that described in the trench method above. Otherwise a firm
foundation plane shall be prepared, which shall be essentially free draining along
the line of the culvert, by trimming the existing ground, or such fill as it is
necessary to place and compact, over a width sufficient to permit satisfactory
construction of the pipe bedding, all to the satisfaction of the E. R. Hard materials
shall be excavated from the pipe foundation over a width equal to the outside
diameter of the pipe to the same depth as specified in the trench method, and
shall be replaced with suitable material uniformly compacted in layers of not more
than 150 mm compacted thickness to provide satisfactory support for the pipe, all
to the satisfaction of the E. R.

Where soft or unsuitable soil is encountered in the foundation, it shall be

excavated over a width of at least 1.5 times the outside diameter of the pipe on
each side of the culvert centre-line to the depth directed by the E. R., and
replaced with suitable material uniformly compacted in layers of not more than
150 mm compacted thickness to provide satisfactory support for the pipe, all to
the satisfaction of the E. R.

3.8.3.2. Backfilling

Backfilling against reinforced concrete pipe culverts and their appurtenant

structures shall be carried out in accordance with the construction methods
described in Sub-Section 3.1.4, using material conforming to the requirements
of Sub-Section 3.1.2.5. Special care shall be taken to properly compact backfill
against the undersides of culvert pipes without disturbing or damaging the pipes
and joints. Backfill shall be built up evenly on both sides of each pipe culvert
along its entire length.

Heavy plant and equipment shall not operate within 1.5 m of any pipe culvert until
backfilling and, where appropriate, pavement construction has advanced to a
stage which provides at least 600 mm of cover to the culvert. Subject to the
approval of the E. R., light compaction equipment may be operated above pipe
culverts after a minimum of 300 mm of cover has been placed and compacted.

3.8.4 Installation of R.C. Culverts

3.8.4.1. General

The type, size and class of pipe to be installed at each location shall be as shown
on the Drawings or as directed by the E. R. Culverts shall not be installed at any
location until the type of pipe, the exact location, the lines, levels and grades, the
length of pipe and details of inlet and outlet structures have been confirmed by
the E. R. In addition, special requirements recommended by the manufacturer
with respect to assembly and installation shall be complied with. Especially where
elliptically reinforced pipe sections are used, care shall be taken to ensure that
the loading axes are positioned exactly vertically.

3.8.4.2. Butt Ended Pipe Culverts with Precast Concrete Collars

The pipes shall be laid on Type A bedding in conformity with the dimensions
shown on the Drawings. Before placing any concrete bedding, the pipes shall be
assembled complete with precast concrete spacing blocks of the same class of
concrete as the bedding material and of sufficient size to eliminate any risk of
settlement of the pipes before or during concreting.

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All joints shall be fully mortared with 1:3 cement mortar before concreting of the
cradle, all to the satisfaction of the E. R. The concrete cradle shall be cast as one
monolithic unit. Alternatively, part of the concrete cradle below the underside of
the pipe may be constructed monolithically at least 24 hours before the assembly
and mortaring up of the pipe sections and collars on condition that shear
connectors are provided across horizontal construction joints to the satisfaction of
the E. R.

During installation, the ends of the pipes shall be butted and the collar centred
about the joint using wedges or other approved means. The annular shall be
completely filled with 1:3 cement mortar with only sufficient water added to
ensure adequate workability and the wedges removed before finally fairing the
joint. Special care shall be taken to ensure that excess cement mortar is neatly
cleaned off. For pipes over 900 mm in diameter the jointing space shall be filled
from inside the pipe after completion of embankment construction using 1:3
cement mortar. When installed, the clearance between the outer diameter of pipe
and the inner diameter of collar shall be at least 20 mm.

Following pipe assembly and mortaring up as above, the remainder of the cradle
shall be cast monolithically, all to the satisfaction of the E. R.

Where vertical construction joints in the concrete cradle are unavoidable due to
circumstances on Site, transfer bars shall be provided to the satisfaction of the E.
R.

Special care shall be taken when placing the concrete cradle to avoid the
entrapment of air underneath the pipe. To eliminate this possibility, concrete shall
be placed to one side of the pipe only until such time as the level of the concrete
surface rises above the underside of the pipe on the side remote from that on
which concrete is being placed. The concrete shall then be brought up at the
same level on both sides of the pipe.

3.8.4.3. Rebated Pipe Culverts

The pipes shall be laid on Type A bedding in conformity with the dimensions
shown on the drawings.

The method of construction shall follow that described in Sub-Section 9.4.2 for
butt ended pipe culverts except for the exclusion of precast concrete collars.
The rebated joints shall be internally flush and fully mortared with 1:3 cement
mortar, all to the satisfaction of the E. R.

3.8.4.4. Spigot and Socket Pipe Culverts

The pipes shall be laid on Type B bedding in conformity with the dimensions
shown on the Drawings. The bedding material shall be accurately shaped by a
template to fit the lower part of the pipe exterior for a height of at least 10% of the
outside diameter of the pipe. Gaps shall be left in the bedding material and
recesses dug in the earth foundation of sufficient width and depth to
accommodate the socket without it resting on the bottom of the recess. The
widths of the recesses in the foundation and the bedding shall both exceed the
width of the socket by more than 50 mm.

Jointing of the pipes shall be carried out strictly in accordance with the
manufacturer’s recommendations, all to the satisfaction of the E. R.

Concrete pipes as specified above shall be laid true to line and level, each pipe
being separately boned between sight rails. Pipes shall be laid in an upstream

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 direction with the sockets towards the inlet and shall rest on even foundations for
the full length of the barrel. Rubber ring joints shall be installed strictly in
accordance with manufacturer’s instruction. Prior to jointing, rubber ring and
jointing surfaces shall be cleaned of all contaminants except for specified
lubricants. The spigot of each pipes shall be inserted concentrically in the socket
of the one previously laid, and the pipe then adjusted and fixed in its correct
position with the spigot correctly entered in the socket.

Care shall be taken to see that the rubber ring is adequately compressed to seal
the joint. All pipes shall be laid to the satisfaction of the E. R.

3.9 PRECAST BOX CULVERTS

3.9.1 Description

This work shall comprise the supply and installation of precast box culverts
inclusive of excavation, backfilling, jointing, bedding, construction of headwalls,
wing walls, aprons and sumps and channel protection works, all in accordance
with this Specification and the details shown on the Drawings.

3.9.2 Materials

3.9.2.1. Precast Box Culverts

Precast box culverts shall be of approved manufacture complying with Australian

Standard Specification 1597 Part 1, or any equivalent alternative standard
acceptable and approved by the E. R.

3.9.2.2. Cement Mortar

1:3 cement mortar for jointing of precast box culvert sections shall conform to the
requirements of Sub- Section 3.4.2.2.

3.9.2.3. Bedding Material

Precast box culverts shall be bedded on Type B bedding as specified in Sub-

Section 3.9.4.

3.9.3 Excavation and Backfilling

3.9.3.1. Excavation for Precast Box Culverts

Unless otherwise directed by the E. R., prior to construction of a precast box

culvert, the earthwork at the required location shall have been first constructed to
a level at least 600 mm above the top of the culvert design levels or to the top of
subgrade levels, whichever is lower, and the precast box culvert shall then be
constructed in a trench excavated in accordance with Sub- Section 3.8.3.1 (b).

Where drainage conditions or other circumstances so require, the E. R. may

direct the Contractor to construct the precast box culvert without first constructing
the earthworks to the level specified above, in which case excavation and
foundation preparation shall be in accordance with Sub- Section 3.8.3.1 (c).

3.9.3.2. Backfilling

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 Backfilling against precast box culverts and their appurtenant structures shall be
carried out in accordance with the construction methods described in Sub-
Section 3.1.4, using material conforming to the requirements of Sub-Section
3.1.2.5. Special care shall be taken to properly compact backfill without disturbing
or damaging the precast box culverts sections. Backfill shall be built up evenly on
both sides of each box culvert along its entire length.

Unless otherwise approved by the E. R., heavy plant and equipment shall not
operate within 2.0 m of any precast box culvert until backfilling and, where
appropriate, pavement construction has advanced to a stage which provides at
least 300 mm of cover to the culvert.

4.9.3 Installation of Precast Box Culverts

The type and size of precast box culvert to be installed at each location shall be
as shown on the Drawings or as directed by the E. R. Precast box culverts shall
not be installed at any location until the exact location, the lines, levels and
grades, the length of culvert and details of inlet and outlet structures have been
confirmed by the E. R. In addition, special requirements recommended by the
manufacturer shall be complied with.

Precast box culverts shall be laid on Type B bedding in conformity with the
dimensions shown on the Drawings. Where specified on the Drawings or directed
by the E. R., Type B bedding shall be laid on a layer of crushed aggregate of
maximum particle size not exceeding 50 mm.

All joints shall be fully mortared with 1:3 cement mortar, all to the satisfaction of
the E. R. In addition, a 3 mm layer of 1:3 cement mortar shall be spread on top of
the legs of the invert in order to ensure uniform bearing between the invert and
lid.

Lifting holes shall be filled with 1:3 cement mortar.

S3-17