Detailed Report about Deep excavation

1. [DOCUMENT TITLE]
[Document subtitle]
[COMPANY NAME]
[Company address]

2. Table of Contents
1. RETAINING WALL ...............................................................................................2
1.1. Gravity wall:-....................................................................................................3
1.2. Sheet pile retaining wall:- ..................................................................................3
1.3. Cantilever retaining walls:- ...............................................................................3
1.4. Anchored retaining walls:- ................................................................................3
1.5. Advantages of concrete retaining walls: .............................................................4
1.6. Case Study:-......................................................................................................4
1.7. Steps of retaining walls construction:-................................................................5
1.8. Advantages of CFA piles:- .................................................................................7
1.9. Disadvantages of CFA piles:-.............................................................................7
2. SOIL NAILING ......................................................................................................8
2.1. Introduction:- ...................................................................................................8
2.2. Applications:- ...................................................................................................8
2.3. Types of Nails Used:-.........................................................................................8
2.4. Materials Used For Soil Nailing:-.......................................................................9
2.5. Procedure of Soil Nailing:-...............................................................................10
2.6. Advantages:-...................................................................................................10
2.7. Disadvantages:-...............................................................................................11
3. DIAPHRAGM WALLS.........................................................................................11
3.1. Introduction:- .................................................................................................11
3.2. Sequence of Work Includes:- ...........................................................................11
3.2.1. Guide wall : ..............................................................................................12
3.2.2. Trench excavation :...................................................................................12
3.2.3. Excavation support : .................................................................................13
3.3. Joining For The Diaphragm Wall Panel:-.........................................................14
3.5. Benefits of Diaphragm Walls:-.........................................................................15
3.6. Disadvantages:-...............................................................................................15
3.7. Case Study: Garage El Tahrir .........................................................................16
4. BRACING IN DEEP EXCAVATION ....................................................................31
4.1. Introduction:- .................................................................................................31
4.2. Case Study: RPSG Office building at Alipore, Kolkata.....................................31
5. REFERENCES .....................................................................................................33

3. 1. RETAINING WALL
A retaining wall is a structure designed and constructed to resist the
lateral pressure of soil, when there is a desired change in ground
elevation that exceeds the angle of repose of the soil.
A basement wall is thus one kind of retaining wall. But the term usually
refers to a cantilever retaining wall, which is a freestanding structure
without lateral support at its top. These are cantilevered from a footing
and rise above the grade on one side to retain a higher-level grade on the
opposite side. The walls must resist the lateral pressures generated by
loose soils or, in some cases, water pressures.
Every retaining wall supports a “wedge” of soil. The wedge is defined as
the soil which extends beyond the failure plane of the soil type present at
the wall site and can be calculated once the soil friction angle is known.
As the setback of the wall increases, the size of the sliding wedge is
reduced. This reduction lowers the pressure on the retaining wall.
The most important consideration in proper design and installation of
retaining walls is to recognize and counteract the tendency of the
retained material to move downslope due to gravity. This creates lateral
earth pressure behind the wall which depends on the angle of internal
friction (phi) and the cohesive strength (c) of the retained material, as
well as the direction and magnitude of movement the retaining structure
undergoes.
They are designed to counteract the force of the ground’s load, either via
their own mass, or by an anchoring system.
There are four main types of retaining wall, which can be created
with different materials:-
• Gravity retaining walls
• Sheet pile retaining wall
• Cantilever retaining walls
• Anchored retaining walls

4. 1.1. Gravity wall:-
Gravity walls depend on their mass (stone, concrete or other heavy
material) to resist pressure from behind and may have a 'batter' setback
to improve stability by leaning back toward the retained soil.
1.2. Sheet pile retaining wall:-
Sheet pile retaining walls are usually used in soft soil and tight spaces.
Sheet pile walls are made out of steel, vinyl or wood planks which are
driven into the ground.
1.3. Cantilever retaining walls:-
Cantilevered retaining walls are made from an internal stem of steel-
reinforced, cast-in-place concrete or mortared masonry (often in the
shape of an inverted T). These walls cantilever loads (like a beam) to a
large, structural footing, converting horizontal pressures from behind
the wall to vertical pressures on the ground below. This type of wall
uses much less material than a traditional gravity wall.
1.4. Anchored retaining walls:-
An anchored retaining wall can be constructed in any of the styles but
also includes additional strength using cables or other stays anchored
in the rock or soil behind it. Usually driven into the material with
boring, anchors are then expanded at the end of the cable, either by
mechanical means or often by injecting pressurized concrete, which
expands to form a bulb in the soil. Technically complex, this method is
very useful where high loads are expected, or where the wall itself
must be slender and would otherwise be too weak.

5. 1.5. Advantages of concrete retaining walls:
• Providing functional support for keeping soil in place,
• Preventing sink holes and eliminating the eye sore of dirt piles and
hills
• Helpful in preventing flooding
• Reduces maintenance and prevents erosion
• Prevent damage to property or surrounding structures
1.6. Case Study:-
In NEW CAIRO CITY AUTHORITY project L-shaped cantilever
retaining walls are used around the whole perimeter of the site. Three
different cross sections thickness are used 50 cm, 30 cm and 25 cm.

6. From (P1:P2:P4:P5) the retaining walls are anchored with the piles and
from (P5:P6:P1) they are not anchored and they counteract the gravity
load by their own mass.
1.7. Steps of retaining walls construction:-
• The formwork of the strip footing is constructed.
• Reinforcement steel is fixed.

7. • The concrete is poured to the level of the 1st basement (3.2m)
• Backfill and compact soil outside the retaining wall
• The formwork of the 2nd level is constructed
• Reinforcement of steel is fixed
• The concrete is poured to the level of the 2nd basement (3.2m)
• The formwork of the 3rd level is constructed
• Reinforcement of steel is fixed
• The concrete is poured to the level of the 3rd basement (3.2m)
The height of the retaining wall is 9.6m covering the three levels of the
basement

8. • With every level the retaining wall is insulated by first applying
bitumen, then applying membrane sheets.
1.8. Advantages of CFA piles:-
• Minimal levels of vibration
• Lower noise levels generated by piling rig
• Faster installation
• More suitable for tension loads at stability elements depending on
ability to install cage prior to concrete drying out.
• Much higher load capacities on larger diameter piles
1.9. Disadvantages of CFA piles:-
• Longer piles required than driven (not driven to a predetermined
set).
• Removal and disposal of spoil material generated from the pile.
• Drilling through large obstructions/boulders cannot be undertaken.
• A strict quality control and thorough supervision need to be done
during the pile installation.

9. 2. SOIL NAILING
2.1. Introduction:-
Soil nailing is being used in many geotechnical applications to improve
stability of excavated vertical cuts and
existing slopes. This paper presents a few case studies on the
stabilization of a vertical cut and improvement of slope stability
using soil-nailing technique. It was found that the vertical cut
stability/slope stability improved due to the reinforcing effect of
nails. The study illustrates that the technique is a viable technique to
improve the stability of vertical cuts and stability of
existing slopes and its advantages need to be exploited on a large scale
in infrastructure projects.
2.2. Applications:-
• Landslide Remediation
• Railway embankments
• Roadway widening under existing bridges
• Stabilizing of existing retaining walls
• Highway embankments and cuttings
2.3. Types of Nails Used:-
• Drilled and Grouted Soil Nail
• Driven Soil Nails
• Self-Drilling Soil Nails

10. 2.4. Materials Used For Soil Nailing:-
• Steel Reinforcements
• Grout Mix
• Shotcreting / Gunite

11. 2.5. Procedure of Soil Nailing:-
• Excavate small cut
• Drill hole for nail
• Install & grout nail
• Place drainage strips, initial shotcrete layer & install
bearing plates
• Repeat process to final grade
• Place final facing on permanent walls
2.6. Advantages:-
• Shotcrete facing is less costly
• Grouting only once is required, saving time and labor.
• The technique is flexible, easily modified.
• Less impact on nearby properties
• Can be used for strengthening of either natural slope, natural or
manmade cut slopes
• Allow excellent working space in front of the excavation face,
• Rapid and uses less construction materials
• Economical

12. 2.7. Disadvantages:-
• Soil nails may not be appropriate, where strict deformation control is
needed.
• Only a very experienced and specialized contractor can implement
this soil mail technique.
3. DIAPHRAGM WALLS
3.1. Introduction:-
• Diaphragm walls are underground structural
elements commonly used for:
i-Retention Systems
ii-Permanent Foundation Walls
• It is an in-situ reinforced concrete structure that is
constructed panel by panel.
• The wall is usually designed to reach very great
depth, sometimes up to 50m.
• Diaphragm walls of shallow depths are often left
unsupported since they are classed as semi rigid
structures.
• However for deeper excavations support is required to
restrict lateral deflections.
• Diaphragm walls are ideal for soft clays and loose
sands below the water table where there is a need to
control lateral movements.
3.2. Sequence of Work Includes:-
a) Construct the guide wall.
b) Excavation to form the diaphragm wall trench.
c) Support the trench cutting using bentonite slurry.
d) Inert reinforcement and placing of concrete to form
the wall panels.

13. 3.2.1. Guide wall :
Guide wall is two parallel concrete beams
constructed along the side of the wall
Guide walls maintain the horizontal alignment and
wall continuity of a diaphragm wall while they
provide support for the upper soil’s depth during
panel excavation.
3.2.2. Trench excavation :
• In normal soil condition excavation is done using a
clamshell or grab suspended by cables to a crane.
• In case of encountering boulders, a gravity hammer
(chisel) will be used to break the rock and then take the
spoil out using the grab.
• The technique involves excavating a narrow trench that is
kept full of an engineered fluid or slurry.
• The slurry exerts hydraulic pressure against the trench
walls and acts as shoring to prevent collapse

14. 3.2.3. Excavation support :
• The sides inside the trench cut can collapse easily.
• Bentonite slurry is used to protect the sides of soil.
• Reinforcement –
Reinforcement is inserted in the form of a steel
cage, but may be required to lap a few sections in
order to reach the required length.
• Concreting –
• Placing of concrete is done using tremie pipes to avoid
the segregation of concrete.
• As concrete being poured down, bentonite will be
displaced due to its lower density than concrete.
• Bentonite is then collected and reused

15. 3.3. Joining For The Diaphragm Wall Panel:-
• Diaphragm wall cannot be constructed continually
for a very long.
• The wall is usually constructed in alternative
section.
• Two stop end tubes will be placed at the ends of
the excavated trench before concreting.
• The tubes are withdrawn at the same time of
concreting so that a semi-circular end section is
formed.
• Wall sections are formed alternatively leaving an
intermediate section in between. The in-between
sections are built similarly afterward but without the
end tube.
• At the end a continual diaphragm wall is
constructed with the panel sections tightly joined
by the semi-circular groove.

16. 3.4. Applications:-
• As permanent and temporary foundation walls for deep
basements.
• In earth retention schemes for highway and tunnel
projects.
• As permanent walls for deep shafts for tunnel access.
• As permanent cut-off walls through the core of earth
dams.
• In congested areas for retention systems and
permanent foundation walls.
• Deep ground water barriers through and under dams
3.5. Benefits of Diaphragm Walls:-
• Can be installed through virtually all soil conditions,
to any plan geometry and to considerable depths.
• Can be constructed ahead of time and independent
of other site activities.
• Can be constructed in relatively low headroom and
in areas of restricted access walls can be quickly
formed several hundred feet deep and through
rock, with good control over geometry and
continuity.
3.6. Disadvantages:-
• They are relatively costly.
• They are also unsuited to strong soils conditions
where penetration is slow and difficult due to the
use of the slurry trench method.

17. 3.7. Case Study: Garage El Tahrir

31. 4. BRACING IN DEEP EXCAVATION
4.1. Introduction:-
The supplementary lateral supports, required for large
excavation depth, are called as Struts. Selection of
struts depends on the earth pressure, available material,
construction period, functionality of the retaining
system etc. Generally wooden, RC & steel struts are
used out of which steel struts are the best choice for a
sizable deep excavation
This soil retaining arrangement is suitable for deep and less wide soil
excavations. Initially, horizontal members are installed against the soil
support. These horizontal members are called as waler. From one
waler to the other, intermediate struts are installed across the
excavation.
4.2. Case Study: RPSG Office building at Alipore, Kolkata
• It has 9.0m deep basement.
• Pile foundation was suggested.
• The project site was almost “T” shaped having almost equal width in
all three arms.
• which has restricted the possibility of island/open excavation.
• Presence of building at close vicinity of the site also restricted the
option of anchored excavation
• The permissible deflection at top of retaining wall was limited to 25-
40mm only.
• Braced excavation has been proposed with
• steel sheet pile and three level struts.
• Vertical H post at
• few locations have been used to reduce the strut section.

33. 5. REFERENCES
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