Construction Technology 2 QS

1. CONSTRUCTION TECHNOLOGY 2
CHAPTER 1.1 DEEP EXCAVATION
GROUP MEMBERS:
LEE SU WEN
LIM JIA YI
CELINE CHONG
YAP SUK PING
KANG YING HONG

2.  You are an engineer in a construction company
which is awarded a tender in basement excavation
and construction using the diaphragm wall method.
The basement is designed for a three (3) storey car
park below a multi-storey office block. You are
assigned to prepare the method statements for this
project which involves the following matters:-

3. WHAT IS A DIAPHRAGM WALL?
 A reinforced concrete structure constructed in-situ panel by panel.
 Constructed using a narrow trench excavated in ground and supported by
an engineered fluid ( typically bentonite mud or polymer mud) until the
mud is replaced by the concrete
 Walls generally range from 600 to 1500 mm thickness, in wide between
2000 and 3500 mm and can be excavated to depths of 60m or more.
 Used for decades to provide cost-effective, long-term solutions for many
groundwater control problems

4. DIAPHRAGM WALL APPLICATIONS
Commonly used for
retention systems and
permanent retaining walls
of the basement
Used as deep
groundwater barriers
As a cut-off provision to
support deep excavation
Used in congested areas
As a separating structure
between major
underground facilities
As the final wall for
basement or other
underground structure

5. Q1. THE CONSTRUCTION OF A
PRE-TRENCH AT THE INITIAL
STAGE OF DIAPHRAGM WALL.

6. GUIDE WALL
 Construct two temporary parallel concrete beams -
guide the excavation tool and to stabilize the upper
 Maintain the horizontal alignment and wall
continuity of a diaphragm wall while are adopted
 Help guide the diaphragm wall grabs vertically and
aid in the positioning of the final structure
 The dimensions and shape - depending on the
nature of the surface soil
 Shall be 100 to 250 mm thick, 1-2m deep and made
of lightly reinforced concrete and shall represent the
reference lines

7. TRENCH EXCAVATION
 Excavation is done by digging technique using clamshell or
grabs to the desired depth.
 Sand and soft rock strata - excavation by cutting technique
using reverse circulation trench cutters can be used.
 Carried out with the aid of several pieces of equipment, such as
(in increasing order of cost):
 Mechanical clam-shell,
 Hydraulic clam-shell,
 Kelly bar
 Hydromill
 The choice of the equipment depends mainly on the
characteristics of the soil to be excavated and on the depth to
be reached.

8. EXCAVATION SUPPORT
 Prevented from collapsing - reinforcing and casting by
the use of supporting bentonite slurry
 supporting slurry fluid must be cleaned - it's
properties are within acceptable levels
 balances the inward hydraulic forces and prevents
water flow into the trench
 The mud is usually pumped to a storage tank where it
hydrates for up to 12 hours.
 The bentonite particles swell and absorb the water
before it’s used to support the excavation.

10. REINFORCEMENT
 A prefabricated reinforced
cage is then lowered into the
excavation between the stop
ends.
 Reinforcement cage must
have a sufficient transverse
and diagonal reinforcement
 to withstand lifting and
lowering handling forces
 Sufficient space must be left
for at least two or three tremie
pipes

11. CONCRETING
 Process of replacing the supporting slurry with the permanent
concrete with the use of vertical pipes - tremies.
 Prevent the segregation of concrete
 Lift the tremies progressively as the concrete level raises
 Maintain a minimum depth of 0.6 meters of tremie pipe into the
concrete.
 Overpouring might be required - make sure that all slurry is
displaced
 Poor tremieing can result in slurry pockets getting entraped within
the diaphragm wall concrete.
 Lead to excessive and costly groundwater leaks or even blowouts.
 Central Artery Project in Boston, MA (Big dig) and has led to
costly repairs and delays.

12. JOINING FOR THE DIAPHRAGM WALL PANEL
 Purpose: to protect the rubber water stop during the excavation of the trench for the
next panel
 It will be remove before the placing of reinforcement and concrete into the excavated
trench
• The steel pipes are installed at both panel
fronts before concreting
• The pipes rest on the excavation bottom
and match the circular shape of the panel
fronts
• Concrete injected takes the shape of the
stop end pipes
• The panel has concave fronts
1. Stop End Pipes

13. 3. DISPOSABLE PIPES
 PVC
 Fixed to the cage and lowered to rest on
the bottom
 A panel with two holes
 When concrete is cast in the secondary
panel, it fills the recess and creates a joint
with the primary panel.
2. Sheet Piling
• Driven into the primary panel, before concrete is
cast
• Concrete on the fronts of the panel takes on the
shape of the sheet pile and a recess is created.
• Concrete has hardened - keep its shape, sheet
piles are extracted.
• Allows for the insertion of plastic elements - water
stops between the panels -guarantee increased
water tightness.

14. WHAT IS EXCAVATION SUPPORT SYSTEM?
keep the sides of deep
excavations stable
1
To withstand soil
pressure and water
pressure (hydrostatic
pressure)
2
ensure that movements
will not cause damage
to neighbouring
structures
3
Preliminary analysis has
to be carried out for
many options of wall
and support system
4

15. TEMPORARY EXCAVATION SUPPORT:
• Only for temporary construction
• can be taken out after constructed
• Reused
• Example:
1. Cantilever wall
2. Soldier pile and lagging
3. Sheet pile- to provide safe access for construction
PERMANENT EXCAVATION SUPPORT:
• Remain in the site
• Example:
1. Diaphragm wall
2. Bore pile
3. Sheet pile- serve as permanent retaining structures

16. Q2. THE SELECTION OF
SUITABLE TEMPORARY
EXCAVATION SUPPORT

17. Cantilever wall
• one type of retaining
structure
• suitable for situation when
the excavation relatively
shallow and the ground is
stiff
• A structure to withstand the
soil pressure and water
pressure.

18. Soldier pile and lagging
• An earth retention technique that
retains soil, using vertical steel piles
with horizontal lagging
• pile can be from the UB (universal
beam) or UC (universal column)
• and are inserted into the pre-bored
holes at the perimeter of the
excavation site for basement

19. Interlocking sheet pile
• H-piles with infilling horizontal
sheeting have also been used
successfully
• Driven in side by side with interlocking
ends
• Light weight
• Can be reused serval times

20. CONSIDERATION OF EXCAVATION SUPPORT
Soil characteristic
Depth of the project
Cost management
Neighbourhood conditions of a site
Construction procedure

21. Soil characteristic
• Can be used in most type of soil
Depth
• Suitable for 3storey basement
Water table • Required dewatering
Costing • Cheap
Neighbour disturbance • Relatively quiet
Construction procedure • Easy and fast to construct
SOLDIER PILE AND LAGGING
Dewatering:
• A process to remove the over-saturated water in ground
• Keep the subsoil within a non-saturated condition.

22. Q3. LIST OUT 6 ADVANTAGES
OF THE DIAPHRAGM WALL
SUPPORT

23. ADVANTAGES OF THE DIAPHRAGM WALL SUPPORT
Reduced number of
joints in the wall
•Improves the walls water
tightness
•Little effects on adjacent
structure
Great depth
Lee Tunnel Project
Diaphragm wall with 98m depth
Quiet and little
vibration
Low environmental impact
* Sound pollution
* Land disturbance
Shorten working period

25. Saving Cost
Less temporary supports
Eg: Labour Cost, Specialist
Contractors
Take Heavy Loads
Used as permanent structure wall
Foundation of the superstructure
Time Management
Faster execution
Prevent liquidated damage

26. PRIMARY & SECONDARY & ENDING PANELS

27. DISADVANTAGES
OF DIAPHRAGM WALL SUPPORT
Less flexible
High cost for short term
project

28. Q4. STATE 2 OF EXCAVATOR
MACHINES

29. EXCAVATOR MACHINES
 Suitable for different kind of
works such as rock excavation,
trenching, etc.
 Suitable for hard surface and
soil
 Control high degree of
verticality
Hydraulic rock cutter

30. HYDRAULIC DIAPHRAGM WALL GRAB
 Suitable for most of soil
conditions
 Controlled by monitoring
system
 High accuracy to verticality
 Excavate over 50m depths
 Free of noise and vibration

31. Q5. WHAT ARE THE SUITABLE STEPS
AND PRECAUTIONS TO TAKE IF
RUBBER WATER STOPS ARE TO BE
CAST AT BOTH SIDES OF THE
DIAPHRAGM WALL?

32. • Mainly to block the passage of
liquid within concrete joints
• PVC is the most commonly used
material for water stops
• Copper and stainless steel and
natural rubber can also be used
• Fundamental object for
construction works to exclude water
RUBBER WATERSTOP

33. PRECAUTIONS
• Pay particular attention to the underside of horizontally
placed waterstops
• Intimate contact between the concrete and waterstop is
necessary for full performance of a waterstop
• Maintain adequate clearance between reinforcing steel and
the waterstop
• To promote the formation of voids due to aggregate bridging
• Waterstop should never be cut or modified to allow
reinforcement to pass through

34. Q6. THE SUITABLE TYPE OF
ADDITIONAL SUPPORT FOR THE
COMPLETED DIAPHRAGM WALL

35. ADDITIONAL DIAPHRAGM WALL SUPPORT
 Commonly used for the
stabilization of steep slopes
which consist of softer soils
 Tendon the steel rods is
connected to the bearing plate
 Help preventing excessive
erosion or landslide
GROUND ANCHOR

36. Q7. THE FUNCTION OF TREMIE
TUBE AND PRECAUTION TO BE
TAKEN WHEN USING THE TUBE

37. PRECAUTIONS
 Transfer concrete under bentonite
slurry which will displace bentonite
slurry when the concrete is filled from
the bottom
 Pour concrete underwater in a way
that avoids washout of cement from
the mix due to turbulent water contact
with the concrete while it is flowing
 Tremie tube has to be cleaned every time
after using, to prevent any excess concrete
to stick on to the tube, that will cause
blockage
 Concrete should be coherent, rich in
cement and of slump between 150 and
180mm
 Lower end of tremie tube should be kept
embedded in the wet concrete
 When a large number of concrete are
required to be placed over an extensive
area, it is advisable to use a number of
tremis
FUNCTION