CONSTRUCTION TECHNOLOGY IV

BQS 552

EARTHWORK
The processes whereby the surface of the
earth is excavated and transported to and
compacted at another location.
Development of a wide range of earthwork
plant (size, capacity and efficiency).

Scale: ranges from small works (the

excavation of ditches and trenches for drainage
and pits and trenches for foundation) to the
large earthworks (highways and dams).
Carried out at an early stage in a construction
project, completion of the earthworks within
the scheduled time is often key to the
completion on time of the whole project.
 SUCCESS OFTEN DEPENDS ON:
An adequate site investigation
and preparing practical and
satisfactory designs of the
The choice and efficient
earthworks use of the correct types
and size of plant to meet
the particular
requirements of the site.
 VARIOUS TECHNIQUES OF
GENERAL EXCAVATION AND THEIR
CONSIDERATION CHOICES
2.1 Bulk excavation
1.1 Site Consideration 2.2 Rock excavation
1.2 Ground Conditions 2.3 Trench excavation
2.4 Support of excavations
2.5 Embankments

1.0 2.0
 Nature of excavation
1.0
GENERAL CONSIDERATION Availability of work area

Disposal of soil
1.1 SITE CONSIDERATION

Existing services and

structures
 1.1 SITE CONSIDERATION
a) Nature of excavation

• The situation of the • Areas of fill require some form of

 A detailed plan of the retaining wall or drainage, prior to
excavation, whether for depositing the spoil; especially when
reduced levels, road movement of soil and planning the sequence of
works, trenches, plant will need to be operations.
basements or pits, have prepared in the case of
to consider the time large cut and fill
available for excavation
• Extended work such as trenches for
operations. pipelines can be divided into
and the sequence of sections and may progress
completed earthworks. simultaneously.
1.0 GENERAL CONSIDERATION
 1.1 Work area' is the total space

SITE CONSIDERATION available for the manipulation of

plant and storage of materials.

b) Availability of work area

It does not include areas for

site administration or On certain sites the work area is sufficient to allow
accommodation the sides of deep excavations to be battered to a
safe angle of repose, thereby giving a work area
The total work area should free from obstructions .
be indicated on a site plan
so that movement of plant It is essential therefore that a study be made of
and materials can be the space available and of the effect progress will
efficiently planned. have on this.
.
 The disposal of soil Immediate use as
1.1 is achieved by one backfilling elsewhere
of the following on the site
SITE methods:

CONSIDERATION
Storage in spoil heaps, for use later Immediate removal
c) Disposal of Soil or removal at a later stage.
from site to other
destination or
dumping areas.
 1.1
SITE
When the material is used for
backfilling it must be suitable They should be positioned
for the particular operation . that they do not interfere

CONSIDERATIO This should involve

with access to work areas
or become a danger or
N separating the cut material
into two categories, the
nuisance because of
damping in bad weather. The removal of spoil from site
may involve the control of
suitable for filling and the
lorries to allow maximum
other for removal or other
c) Disposal of Soil earthworks.
utilization of earthmoving
plant.

Consideration must also be

given to the stresses
induced by spoil heaps on Some consideration must also be
Consideration should be given
structures or services below given to spillage of soil when
to the position of such spoil
ground or adjacent to the leaving the public highways must
heaps in order.
spoil heap. be kept clean at all times.
 1.1
SITE CONSIDERATION Care should be taken to
establish the position of all pipes,
cables and underground services,
which should be clearly marked
d) Existing Services and Structure before, earth works commence.

Where excavation involves the

disturbance of services, they
should be carefully unearthed and
supported to prevent damage by
movement or vibration;
nevertheless, breakages almost
invariably occur.
 1.1

SITE CONSIDERATION
d) Existing Services and Structure
Existing structures adjacent to excavation areas will require support during
excavations. This may take any of the following forms:

CUT OFF WALLING STRUTTING AND SHORING (SHEET PILES) UNDERPINNING

A thin, watertight wall of clay or The process of strengthening and
concrete built up from a cutoff A pile in a row of piles driven side stabilizing the foundation of an
trench to reduce seepage. by side to retain earth or prevent existing building or other
seepage. structure.
CUT OFF WALLING UNDERPINNING
STRUTTING AND SHORING (SHEET PILES)
 Consideration must be
given to the change in
soil stability due to
The information adverse weather
obtained from the site conditions.
investigation will assist
following factors:
2.0
a) Ground support
The ground support GROUND CONDITIONS
required during
excavation. required will depend on the
b) Method of keeping strength soil, the depth of
the excavation free from excavation and the length of
water. time that the excavation
c) Plant to be used. remains open.
 2.0
2.1
VARIOUS TECHNIQUE OF
BULK EXCAVATION.
EXCAVATING AND THEIR
CHOICES

2.2 2.3
ROCK TRENCH
EXCAVATION. EXCAVATION.

2.4 2.5
SUPPORT
EXCAVATION. EMBANKMENTS
 2.0
VARIOUS TECHNIQUE OF EXCAVATING
AND THEIR CHOICES

Bulk excavation may include the

2.1
following operations :

• Cuttings
Bulk Excavations • Cut and fill areas
Groundworks which remove large • Basements and large pits
amounts of materials and reduce the
general level down to near formation. • Hand excavations
They are made with large and efficient
excavators.
 Done for canals, roads and similar
form of construction.
Used of plants depend on :
i) Quantity of soil to be
transported
ii) Distance of disposal unit
iii) Conditions of ground and
water level

2.1
BULK EXCAVATION
Examples of plants:
i) Bulldozers
ii) Scrappers
iii) Dragline
iv) Combination of plant track mounted
excavation
a) Cuttings v) Face shovel
BACKACTOR BULLDOZER
DRAGLINE
DUMPER
 BACKHOE
FACE SHOVEL
ROLLER COMPACTION SCRAPPER
TRENCHER SKIMMER
 Shallow cut and fill operations occur in road
works and airfield construction.

In shallow excavation the plant may have to stop

work to prevent damage of the formation level,
or temporary works may have to be provided
over large areas, either way resulting in extra cost.

Areas of cut and fill can be adequately

drained by temporary trenches, which into
the final sub-grade drainage.

2.1
The formation level may be protected
BULK EXCAVATION against water and the drying-out action of
b) Shallow cut and fill wind and sun, by some form of waterproof
dressing.
2.1BULK EXCAVATION
c) Basement construction
Synonymous for deep pit excavation over
4.5m deep.

Methods of excavation:
i) Open cut excavation
ii) Cut and cover techniques
iii) Top down techniques
iv) Composite techniques
OPEN CUT EXCAVATION CUT AND COVER
TOP DOWN TECHNIQUE
COMPOSITE TECHNIQUE
For construction purposes the term 'deep
pit', which applies to excavations over 4.5m
deep, is synonymous with the term
'basement'.

Shallow pits, which are 1.5 m deep, present

little or no problem in terms of excavation or
ground support. They are normally excavated
with a small back acting machine or by hand.

Medium pits, classified as 1.5 to 4.5 m deep,

require careful selection of plant and ground
support.

BULK EXCAVATION
c) Basement construction
 BULK EXCAVATION
c) Basement construction
Methods of excavation of
basements and deep pits are
varies.

The following are supporting

methods commonly used by Unshored excavation
contractors in protecting the
excavated area:
i) Unshored excavations
ii) Shored excavations
iii) Dumpling method
iv) Cut-off walling method
Shored excavation
Dumpling method
This is used where there are buildings or street in the
proximity.

The method is to construct a series of retaining wall in trench,

section by section, around the site perimeter ,leaving a centre
called "dumpling
Cut off walling method
•The word “Cut-Off” is meant to define the
specific purposes of this technology, i.e. to
either stop the flow, to “Dam” the
underground stream, or to surround and
seal-off an area, to prevent water inflow and
water outflow from the encircled area.

•The principal types of vertical cutoff walls

are sheet pile walls, geomembrane walls,
and slurry trench cutoff walls.
 BULK EXCAVATION
c) Basement construction
Consideration on the Choice
of support being used

Unshored excavations can be

assumed there is an ample
All the methods being With shored excavations, the
working space around the
choose have an effect on shoring can be made watertight
excavation to allow battering
the choice of plant to be by sealing the joints of sheet
of the excavation.
used. piling, thereby eliminating the free
flow of water.
This will allow more freedom of
choice in excavating plant than
the other methods.
 Excavating deep
basements and pits to use

2.1
pneumatic tools such a
clay-spades and picks.

This will occur in excavations which are heavily supported,

BULK EXCAVATION leaving little room for mechanical excavation;

it will also be necessary in the vicinity of services which
d) Hand Excavation would be subject to damage by machine, or to the case of
removing obstacles such as boulders (large rocks), logs
(timber) or other projecting objects.
Spoil from such excavations would be put into skips for
periodic removal.
d) Hand Excavation
 2.0
Breaking by hand Pneumatic breaker VARIOUS TECHNIQUE OF EXCAVATING
(hammer & wedges) AND THEIR CHOICES

Drilling with pneumatic

2.2 ROCK EXCAVATION
Vary depending on:
machine : blasting
i) Types of materials
ii) Quantity involved
iii) Conditioned of site
Drilling with pneumatic
machine : freezing liquid iv) Equipment available
Methods that use:
 The first three methods are suitable where any of
the following conditions prevail:

The noise of blasting would cause annoyance

2.2 Adjacent buildings may be subject to damage.

ROCK Blasting may cause inconvenience or stoppage

of traffic.
EXCAVATION Landslides or rock falls might result.
Accurate cutting is necessary and excessive
'over break’ would be uneconomical.

Overbreak is defined as the unwanted

removal of rock beyond a specified
maximum excavation perimeter
 2.0
VARIOUS TECHNIQUE OF EXCAVATING
a) Purpose for which the trench AND THEIR CHOICES
is being excavated

b)The nature of the ground

c)The time scale of the work 2.3

TRENCH EXCAVATION
d)Ground water conditions
Choice of Methods depends
on:
e)The location of the trench

f) Number of obstructions
 2.3
Trench Excavation

The methods of
a) Full depth, full excavating c) Stage depth,
length trenches are as successive
excavation follows: stages

b) Full depth,
successive
stages of
excavation
 2.3
This method is suitable for long
narrow trenches of shallow depth in
which the machine completes the
trench non-stop ahead of any other
operation. This method is suitable for
pipelines and sewers

a) Full depth, full length excavation

 2.3
This method is suitable for deep
trenches where several operations of
work can proceed in sequence; this
would prevent stretches of trench from
being left open too long and thereby
being subject to collapse.

b) Full depth, successive stages of

excavation
 2.3
This method is suitable for very deep
trenches in confined areas or adjacent
to existing property. It involves the
support of the trench as the work
proceeds and is most suited for
operations such as deep foundations
and underpinning.

c) Stage depth, successive stages

of excavation
2.4
2.0
VARIOUS TECHNIQUE OF EXCAVATING
AND THEIR CHOICES

▪ Support of excavations is governed

by the following factors:
i) Type of soil
Support of Excavations
ii) Ground water condition
iii) Depth and width of excavation

The soil types for discussion are as follows:

i) Loose sand, gravel and silts.
ii) Compact sands and stiff clays
iii) Rocks
Support for excavation in loose sand,
Support of Excavation
2.4
Since such soils are likely to slump quickly, the
gravel and silts requires some form of support must be placed immediately after
excavation takes place'. This means that deep
continuous support, which may consist of: excavations will have to be dug in stages:

i) The first stage by machine

a) Trench sheeting - lightweight
pressed steel sheets ii) and, after supporting the first stage,
any subsequent stages by hand or by
b) Steel sheet piling grab.

Hand excavation is very expensive and

therefore the use of driven sheet piles
may be more suitable for deep trenching.
a) Trench sheeting - lightweight pressed steel
sheets

b) Steel sheet piling

 Support of Excavation
Compact sand and stiff clays

Support for this type of soil can be

2.4
If the soil is subjected to
achieved by using open timbering
drying out and crumbling,
support.
the spacing of the pooling
Boards can be reduced
Involves the use of pooling boards or
accordingly.
trench sheets at intervals of
approximately 1 meter; the board are Dry clays which take up rain

supported by continuous walling and water and expand: this

trenches jack at 2 meter centres. produces extra stress in the

struts and allowance should be
made for this at the design
stage.
 2.4
Support of Excavation
Rock
Rock bolting consists of solid steel rods which
are fixed in deep drill holes by means of
Support to rock excavation depends to wedges, sleeves or grouting process; light steel
sections or steel plates are used to support the
large extend on the type of rock and the rock face through which the rods are threaded.
slope of rock strata.

In the case of unstable rock faces, open

timbering should be used to prevent any
slump/collapse.

Where the depth of excavation is

Support of these materials may be
excessive, the rock face may be stabilized
expensive; It may be more economical to
by rock bolting.
cut these back to a safe angle of repose if
space allows such treatment.
Rock Bolting
 2.0
VARIOUS TECHNIQUE OF EXCAVATING
AND THEIR CHOICES

2.5 Embankments
Em·bank·ment : a wide wall of earth or stones
built to stop water from flooding an area, or to
support a road or railway
The construction of embankments and the design profile of the
sloping sides will depend on a number of factors, such as:
2.5
Embankment

The extent to which the The difficulties in

The consolidation of strength properties of the fill construction during
the fill in the may be affected by the adverse weather, when
embankment under method of construction. using clays and fine sands.
the proposed loads.

2 4
6
1 3
5
The purpose for which
the embankment is The stability of the The cost of obtaining
constructed, e.g. the ground on which the suitable fill material.
loads involved. embankment is to be
constructed.
The method of constructing an embankment
Embankment
2.5
will depend upon the extent of the works, the
type of fill material being used and the nature
of the site.

The site must be stripped of all vegetable

matter.

Fill material should be tipped and spread in layers of

such a thickness that it can be compacted to, the
required density – which will be established by
laboratory testing
Where large volumes of fill are involved, the
density factor obtained in the laboratory may
Embankment
2.5
not be achieved on site.

This discrepancy can be minimized by the

correct selection of compaction plant: the
plant most suited will depend on the soil type
and its working moisture content.

Difficulties in varying the moisture content of

large volumes of earth between the two
stages of excavating and filling
 2.5
Embankment slope

i. The safe angle of any embankment slope will depend on the nature of the fill material used and the
height of the bank.

ii. The safe angle will range from as much as 45’ for rock waste fill down to as little as 20’ for some
clays.

iii. Slopes may also be stated as ratios and percentages . e.g: a slope of 1:3 or 33% , a slope of 1:5 or
20%
Construction of access
embankment and
container terminal site
THE END
The end