Deep excavation

13/10/2016 Advance construction technology 1

prepared By:
Mali Amit 146510306033
Mehta dishant 146510306037
Modi yash 146510306038
Garva Amit 146510306022
Guided By:
Prof. h.r.solanki
CIVIL ENGINNERING

content
Excavation
Timbering of trenches
dewatering

Deep excavation
13/10/2016
Advance construction technology
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Deep excavation

Excavation
A mane made cut, cavity, trench, or depression formed
by earth removal.
Fig 1. excavation

 Excavation is one of the
most hazardous
construction operation.
 Most accident occur in
trenches 5 to 15 (1.5m to
4.8m)feet deep there is
usually no warning
before a cave in .

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Shallow excavation Deep excavation
Excavation

Shallow excavation
When the depth of excavation is less than or equal to
the width of excavation,it is called shallow
excavation.
For shallow excavation, normally the depth of
excavation is less than 1.5m.
No support is required to support the sides of trench,
i.e, no timbring to trenches is required.
No water is met with during the process of excavation
of the trench, hence dewatering is not necessary.
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Deep excavation
When the depth of excavation is more than the
width of excavation is called deep excavation.
For deep excavation, normally the depth of excavation
is more than 1.5m.
Timbering to trenches is required to support the sides
of trenches.
Dewatering is required.

Timbering
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TIMBERING OF TRENCHES

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Necessity of timbering
Components of timbering
Reason of providing timbering
Methods of timbering
Precautions to be taken during timbering

Necessity of timbering:-
For the safety of the excavating labours.
For the safety of the the foundation of adjoining
structures.
For the safety of people and traffic passing near the
excavation.
For the safety of public service lines like telephone
cable, water supply pipes, electric cable, drainage
line,etc.

Components of timbering
1. Polling board
2. Sheeting
3. Wales OR Walling
4. Strut
5. Bracing
6. Runners

Fig.2 Vertical sheeting Fig.3 runners
Components of timbering

Reasons of providing timbeting
When the depth of trench is more.
When the sub soil is loose.
When the side of trench is slip.

Methods of timbering
1.Stay bracing
2.Box sheeting
3.Vertical sheeting
4.Runners
5.Sheet piling

1. Stay bracing
This methods is usedwhen excavation is to be carried
out in moderately firm ground and when the depth of
excavation does not exceed 2.0 m.
The vertical sheets orvpolling Bords are placed
opposite each other against the walls of the trenche and
they are held in possition by one or two rows of strut.
The sheets are placed at an interval of 3 to 4
m.Generally, they extend to the full depth of the
excavation.

www.abuildersengineer.com
Fig.2 stay bracing

Fig.3 stay bracing

2. Box sheeting
This method is
used in loose soil
and when the
depth of
excavation does
not exceed 4.0 m.

Fig.4 box sheeting

3. Vertical sheeting
This system is adopted for deep trenches (upto 10 m
depth) in soft ground. The method is similar to the
box sheeting except that the excavation is carried out
in stages and at the end of each stage, an offset iS
provided, so that the width of the trench goes on
decreasing as the depth increases. Each stage is
limited to about 3 m in height and the offset may vary
from 25 to 50 cm per stage.

Fig.5 vertical sheeting

4. Runners
This system is used in extremely loose and soft
ground, which needs immediate support as excavation
progresses. The system is similar to vertical sheeting,
except that in the place of vertical sheeting, runners,
made of long thick wooden sheets or planks with iron
shoe at the ends, are provided. Wales and struts are
provided as usual. These runners are driven about 30
cm in advance of the progress of the work, by
hammering.

Fig.7 runners

5.Sheet piling
This method is adopted when,
• soil to be excavated is soft or loose
• depth of excavation is large
• width of trench is also large and
• there is sub-soil water.
Sheet piles are designed to resist lateral earth pressure.
These are driven in the ground by pile driving
equipment.

Precautions to be taken during
timbering
1. Slip of earth
2.Testing of strut
3. Bending of wales
4.Movement of timbering members
5.Removal of timbering
6.Safety helmet
7.Ladder
8.Traffic control
9.Tools

10. Supervision
11. Shelter
12. Fencing & lights
13.protection of adjoining structures

Dewatering

content
Definition of dewatering
Situation required dewatering
Methods of dewatering

 Definition :
It is a process of removal of excess water from
saturated soil. Dewatering of trenches is very pervious
soils poses a main problem of seepage water entering the
pit.

Situations requiring dewatering
• Deep excavation
• Construction in water logged area.
• Marine structures.
• Ground water table is high.

Various methods of dewatering
1. pumping method
2.Sumps & ditches
3. Deep well system
4.Well point system
5.Cement grouting
6.Chemical process
7.Freezing process
8.Electro-osmosis method

1. pumping method
•This method is used for small work like , water remove
from shallow trench , water remove from foundation
etc.
•This method is very easy method compare to another
method.
•In this type of method centrifugal pump is used.

2. Sumps & ditches
This is simplest methods of dewatering used in
shallow excavations in coarse grained soils. In this
methods ,shallow pits, called sumps are dug along the
periphery of the area. These sumps are connected by
ditches or drains of semicircular in shape and 20cm
diameter, along the periphery of the excavation. The
water from the slopes or sides flows under gravity and
is collected in sump from which it is pumped out.

3. Deep well system
Deep well dewatering systems enable one to
lower the groundwater table to a considerable
depth. A submersible pump is installed at the
bottom of the well, of which the casing generally
has a minimum diameter of 150 mm. The discharge
pipes from the submersible pumps of a number of
adjacent wells are connected to a common delivery
main. The water is raised from the well by a multi-
staged pump

4. Well point system
 A line or ring of small
diameter shallow wells
(called well points)
installed at close spacing
(1 to 3 m centers) around
the excavation.
 Commonly used for
dewatering of pipeline
trenches

Multiple stage system

5. Cement grouting
The purpose of the grout curtains are used under
dams where the foundation would otherwise pass too
much seepage, reduce the seepage erosion potential
and reduce leakage through the dam foundation.
Grout curtain is restrict seepage to such an amount
that it does not cause too much loss of storage, and
does not dislodge the foundation downstream or erode
the base of the dam.

6. Chemical process
 In this method chemicals in the liquid form is pumped
into and through very small openings, which other
grout cannot penetrate.
 Two chemicals solutions of sodium silicate and
calcium chloride are used.
 This process is useful when sand having effective size
greater than 0.1mm.
 This process is very much expensive and not used
under Favorable conditions.

 Fig off chemical process

7. Freezing method
This process is suitable for excavation in water logged
soils like sand, gravel and silts .it is advantageously used for
deep excavations such as for bridges, etc . specially when
the excavation is to be made adjacent to an existing
structure or near some water ways.
The process consist in forming a wall of ice by
freezing the soil around the area to be excavated. Freezing
pipes encasing smaller diameter inner pipes are sunk above
one meter c/c along the periphery of the area to be
excavated. The lay out the pipe should preferably be such
that area enclosed is circular in plan. Freezing liquid is
then supplied to the freezing pipes by refrigeration plant.
This make the ground around the area to be excavated.

29/9/16 advance construction technology 50

Pipes prior to freezing
Following initiation of freeze
Closure of frozen earth wall
Complete frozen earth wall

8. Electro osmosis method
Electro-osmosis method of drainage is used for
fine grained cohesive soil which can be drained or
stability using electric current. This method was
developed by L.Casagrande (1952)
If d.c. is passed between two electrodes driven
into natural soil mass, the soil water will travel from
the positive electrode (anode) to the negative
electrode(cathode) the cathode is made in the form of
well point or metal tube for pumping out the seeping
water .the spacing of electrode is 4 to 5m .

Reference
 http://civilassistaustralia.com.au/service/ground-
water-control/
 ^ The adaptable wellpoint. JK White. Water Services,
May 1982.
 https://en.wikipedia.org/wiki/Dewatering
 www.wellcore.co.za/downloads/Dewatering_Well_Po
ints.pdf
 Advance construction technology book(Dr. R. P.
Rethaliya )

Deep excavation

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