Diaphragm wall are similar to shear walls in underground construction

1. UNDERWATER CONSTRUCTION OF
DIAPHRAGM WALLS
CHINNU MARIAM NINAN
ASSISTANT PROFESSOR
DEPARTMENT OF CIVIL
ENGINEERING
TKM COLLEGE OF ENGINEERING

2. DIAPHRAGM WALLS
• “Diaphragm walls are underground structural elements
commonly used for retention systems and permanent
foundations walls.” (to prevent the seepage of water into
the excavated areas).
• Used as a deep groundwater barrier
• Diaphragm wall is a reinforced concrete structure
constructed in-situ panel by panel (or pre-cast). The wall is
usually designed to reach very great depth, sometimes up to
50m
• Diaphragm Wall is generally reinforced concrete wall
constructed in the ground using ‘Under slurry technique’
which was developed in Europe
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3. • Diaphragm wall is a continuous wall constructed in
ground in to facilitate certain construction activities,
such as:
• As a retaining wall
• As a cut-off provision to support deep excavation
• As the final wall for basement or other underground
(e.g. tunnel and shaft)
• As a separating structure between major underground
facilities
• As a form of foundation (barrette pile –rectangular pile)
• The wall is usually designed to reach very great depth,
sometimes up to 50 m.
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4. 4

5. COMMON USES OF DIAPHRAGM
WALLS
• Structural support for the construction of building
basements with underground parking.
• Add stability to landslides, highway cuts and deep building
excavations including circular shafts.
• Provide retaining walls in areas where severe limitations
may be posed by noise, vibration, geology, water table etc.
• Provide deep diaphragms where geometric precision and
continuity at depth are vital for structural and hydraulic
reasons.
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6. ADVANTAGES OF DIAPHRAGM WALLS
• Suitable for unstable soil profiles below water table.
• Limited construction time.
• Where deeper than normal cantilever support may be
needed.
• Designable to carry vertical loads.
• Construction time of basement can be reduced.
• Minimize the settlement of adjacent / differential
settlement
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7. METHODS OF CONSTRUCTING
DIAPHRAGM WALLS
Slurry Trench Technique RC Continuous Diaphragm walls / Cast-in-situ
Use of bentonite Pre cast diaphragm walls
Soil mixing wall method (SMW) Glass diaphragm walls
Sheet pile walls
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• Slurry Trench Technique: 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. Slurry trench excavations can be performed in all types of soil even
below ground water table.
• Use of bentonite: Bentonite (5% bentonite and 95% water) is a trench stabilizing fluid
having cementitious property. It is a type of soil that have expansive property. It is mixed in
water and hydrated for 48 hours to get a density of 1.2. Along with deep excavation,
bentonite is poured into the trench. When poured in the diaphragm wall shaft, it reacts
with the soil to make a stabilizing gel to stabilize the vertical surface.

8. • Soil Mixing Wall Method (SMW): This is the method used to make continuous walls by
churning up piled soil using auger, pouring in cement milk and making soil mortar
columns in the ground using soil as an aggregate.
• This is an in-situ mixing and churning process.
• In this method, after completing the excavation of the trench, soil-cement mix is produced
by mixing and churning excavated soil.
• The excavated soil is classified and graded with cement milk after being put through a
tremie. Then the soil-cement is poured into the trench, after which steel material is built in,
as the core material.
• Glass diaphragm walls: For a contaminant enclosure, a diaphragm wall system
consisting of special glass panels with a sealing made out of glass are used. The panels
are 50 cm wide and upto 50 m long.
• Properties of glass: high degree corrosion resistance, impermeable, resistant to chemical attack &
potential water seepage, low maintenance cost, can be custom-made.
• Sheet pile walls: interlock edge to edge to form a diaphragm continuous wall and can
carry large compressive loads, tensile and flexural loads.
• Sections of steel, wood, concrete, precast, aluminium, plastic
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9. THE PRECAST DIAPHRAGM WALL
• A continuous trench or longer panel is excavated under self-hardening cement –
bentonite slurry.
• The slurry is retarded to remain fluid during construction.
• After a sufficient length of excavation is complete, a crane lifts the precast wall
section into the trench.
• The cement bentonite slurry sets to form the final composite wall.
• Alternatively, the trench is excavated under bentonite slurry, which is then
displaced with cement bentonite slurry.
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10. CAST – IN – SITU DIAPHRAGM WALLS
• The trench is being excavated in discontinuous sections or “panels”.
• Stop-end pipes are placed vertically at each end of the primary
panel to form joints for adjacent secondary panels.
• Then a steel reinforcement cage is placed in the centre of the panel.
• Concrete is poured in one continuous operation through one or
more tremie pipes that extend to the bottom of the trench.
• The tremie pipes are extracted as the concrete rises.
• The slurry that is displaced by the concrete is saved and for
subsequent panel excavations.
• As the concrete sets, the end pipes are withdrawn.
• The finished wall may be cantilever or require anchors or props for
lateral support.
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11. MATERIALS
• Cement: Cement shall be
• ordinary Portland cement conforming to IS 269 : 1989
• rapid hardening Portland cement conforming to IS 8041: 1990
• blast furnace slag cement conforming to IS 455 : 1989
• Portland pozzolana cement conforming to IS 1489 (Part 1) :
1991 or IS 1489 (Part 2) : 1991.
• Aggregates (CA): The aggregates shall conform to IS 383 :
1970. Well graded coarse aggregate of 20 mm size shall
normally be used in reinforced concrete diaphragm
functions of the diaphragm wall as an under- walls. For
plastic concrete diaphragm walls, a smaller size of
aggregate may be used.
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12. • Sand (FA): Well graded sand consisting of 50 percent
coarse sand shall be used.
• Water: Clean water free from deleterious impurities, as
specified in IS 456 : 1978, shall be used in preparing the
concrete mix and for preparation of bentonite slurry.
shall be free from salinity when used with bentonite.
• Admixtures: If required, chemical admixtures in concrete
shall be used as specified in IS 456 : 1978.
• Reinforcements: Mild steel bars conforming to IS 432
(Part 1) : 1982 and cold worked bars conforming to IS
: 1985 shall be used.
• Bentonite: Bentonite used shall conform to IS 12584 :
1989.
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13. 13
SPECIFICATION OF BENTONITE SLURRY

14. • Test to determine density, viscosity, shear strength and pH value shall
be carried out until a consistent working pattern is established,
taking into account the mixing process, blending of freshly mixed
bentonite slurry with previously used slurry and any process which
may be employed to remove impurities from previously used
bentonite slurry.
• When results show consistent behaviour, the tests for shear strength
and pH value may be discontinued and tests required to determine
density and viscosity need to carried out.
• The frequency of testing shall be on panel to panel basis where
bentonite slurry becomes heavily contaminated with fine sand
during its first use, and may be on daily basis where contaminating
may be slight.
• Prior to placing of concrete in any panel a bentonite slurry sample
shall be taken (that is about 0.2m from the trench bottom) and the
same shall be tested for density.
• The density thus determined shall not be greater than 1.25 g/ml to
ensure satisfactory placing of concrete.
• If the slurry is found to have higher value, the same shall be thinned
by feeding in fresh bentonite till the required density is achieved.
• Suitable slurry pumps, submersible pumps or air lift shall be used in
replacing the contaminated slurry at the bottom of trench by fresh
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15. BENTONITE SLURRY AND ADDITIVES
• Sodium bentonite powder shall be mixed thoroughly with potable water to form a fully
dispersed lump – free homogeneous slurry.
• Suitable slurry tanks shall be used for this operation. The use of a slurry pump with
special nozzle is suggested for preparing bentonite slurry.
• Use of paddle stirrer or other mechanical devices such as colloidal grout mixer, may also
be made for proper mixing of slurry. The temperature of water used and slurry used shall
not be less than 5 degree C.
• Where saline or chemically contaminated ground water is present, special additives may
be used to render bentonite slurry fit for use. These additives are used in very small
amount of 0.1 to 0.5 percent by mass of slurry.
• Ferrochrome lignosulphonate in combination with soda ash or dichromate of soda, may be used for
effective bentonite hydration, if hardness of sea water exceeds 200 ppm.
• Sodium carboxymethylcellulose(S.C.M.C.) - protects slurry against effects of electrolytes, accelerates
filter cake formation and reduces fluid loss by increasing the viscosity of slurry.
• Cement contamination may be counteracted by phosphates. The calcium gets removed
and clay solids get dispersed. Phosphates decrease pH value thereby lowering viscosity
and yield value of slurry.
• Carboxymethylcellulose, gums or preheated asbestos may be used to increase viscosity
and reduce filter loss.
• To remove fine salty solids and clay solids from the slurry, flocculants may be used Vinyl
acetate maleic anhydride co-polymer or polyacrylamides may be used.
• Pre-gelatinised starch may be employed as a fluid loss control. It may also be used as a
protective colloid against the effect of electrolytes.
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17. DIAPHRAGM WALL CONSTRUCTION PROCESS
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18. GUIDE WALLS
• Guide wall shall be constructed prior to main slurry
trenching operation.
• Guide wall shall be 100 to 250 mm thick, 1 to 2 m deep
and made of lightly reinforced concrete, and shall
represent the reference lines.
• In soft ground or fill, guide walls may be taken deeper.
When ground water table is close to surface, guide wall
shall be constructed higher than the surface level to
maintain additional slurry head.
• The clearance between finished diaphragm wall and guide
may be 50 mm minimum for straight panels.
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19. • The clearance shall be suitably increased when the panel
are curved. The finished faces of the guide walls toward the
trench shall be vertical.
• Guide wall after construction should be suitably propped
to maintain specified tolerance. Mesh or cage
reinforcement shall be used in guide wall.
• The level of bentonite slurry in the trench shall be 1 m or
more, if necessary, higher than the ground water table.
• For heavy machinery, guide wall shall be constructed with
suitable ground slab (on both side of wall).
• Construction of guide walls should be done continuously.
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21. STAGES OF CONSTRUCTION OF CAST-
IN-SITU DIAPHRAGM WALL
• Cast-in-situ structural RCC diaphragm wall shall be
constructed by resorting to either successive panel method
or alternate panel method.
• In successive method, a panel shall be cast by the side of
another completed panel, so as to form a good joint and
continuous leak proof diaphragm wall.
• In alternate panel method, primary panels a shall be cast
first, leaving suitable gaps in between. Secondary panels
shall then be cast, resulting in a continuous diaphragm
wall..
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22. SUCCESSIVE PANEL METHOD
• In this method a panel shall be cast in continuation of
previously completed panel.
• Use of form tubes is generally used for creating a joint
between primary panels and secondary panels.
• However with larger width of diaphragm wall and greater
depth of diaphragm wall it may not be possible to provide
form tube due to handling, lowering and extraction
difficulties.
• In such a case special tools, such as semicircular chisels
are used to effect a joint between primary and secondary
panel and in this case form tubes are eliminated.
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24. ALTERNATE PANEL METHOD
• In this method primary panels shall be cast first leaving
suitable gaps in between. Secondary panels shall then be
cast in these gaps. Two stop end tubes are used at the
ends of the primary panels to support concrete and to
form suitable joints with the secondary panels.
• The excavated length of trench for secondary panel may
be smaller than that of primary panel.
• The shape of the secondary panel end should be such as
to form a good joint with primary panels.
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26. CONSTRUCTION METHOD
• Excavation of each trench panel shall be done with the
help of suitable machinery.
• The trench panel shall be kept filled with bentonite slurry
of suitable consistency and viscosity during the
excavation period.
• A stop end tube with a smooth surface, or a structural
section shall be inserted in the trench at the end of the
panel to support concrete and to form a suitable joint
with the next panels.
• Reinforcement cage shall then be lowered in the trench
panel and suitably supported.
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27. EXCAVATION OF TRENCH
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28. • Bentonite slurry to balance the soil pressure to protect the
trench from collapse.
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29. INSERTING REINFORCEMENTS
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30. CONCRETING THROUGH TREMIE PIPES
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31. TRENCHING EQUIPMENT
• Depending upon the type of soil encountered at the site,
and dimensions (depth, length and thickness) of
diaphragm wall to be constructed, suitable trenching
equipment shall be closed.
• The general trenching equipment shall include rotary
boring rig, percussion boring rigs, trenching bucket type
shovels, mechanical grabs, hydraulic grabs, grabs with
key bar, direct mud circular boring rigs, reverse mud
circular rigs.
• For gravelly soil, boulder deposits and rock formations,
specially designed chiseling equipment shall be
considered. 31

32. GUIDING FRAME WITH CUTTING
DRUM
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33. SLURRY PREPARATION AND
TESTING EQUIPMENT
• Tanks of suitable size and slurry pumps of suitable capacity
should be used for storage, mixing and circulation of
bentonite slurry at a site.
• A separate water pump may be used for water supply to
slurry tank.
• Equipment for sampling the slurry from deep trenches and
testing its concentration, viscosity, pH values and hardness
of ground water in which the bentonite slurry and concrete
are prepared, should also be used
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34. CONCRETING EQUIPMENT
• Concrete mixer, tremie pipes of suitable length and size
and concrete pouring devices should be used according
to the need of work.
• The lifting arrangement for tremie pipes should be
capable of doing the work with desired speed.
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35. LIFTING DEVICE
• Cranes of suitable capable and boom length should be
used in the case of precast wall panels for lowering them
in the trenches. The same may be used for stacking the
panel at site or during casting the panels in the casting
shed.
• The reinforcement cage of large depth and length of wall
panels may be lifted by crane.
• If the load of the panels and reinforcement cage are
small, this work may also be done by which and pulley
arrangement provided on the diaphragm walling ring.
• Cranes or rigs with winches of adequate capacity may be
used for operating the trenching grabs as necessary.
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36. GENERAL GUIDELINES
• Choose the rotary, percussion, grabbing equipment, and
equipment for direct or reverse mud circulation, etc.
according to need
• Vibration and noise produced during construction should
not have any damaging effect on the people and existing
structure.
• Consideration shall be given in selection of equipment
when they are required to work on a site with restricted
space or head room.
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