DIAPHRAGM WALL CONSTRUCTION STAGES
A diaphragm wall is constructed in following stages :
Stage 1 : Construction of Guide Wall
Guide walls shall be constructed prior to main slurry trenching operation.
Guide walls 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 walls higher than the surface level shall be constructed to maintain additional slurry head.
The clearance between finished diaphragm wall and guide may be 50 mm minimum for straight panels.
The clearance shall be suitably increased when the panels are curved.
The finished faces of the guide walls towards the trench shall be vertical.
Guide walls after construction should be suitably propped to maintain specified tolerance.
Mesh or cage reinforcement shall be used in guide walls.
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 walls shall be constructed with suitable ground slab (on both sides of the walls).
Guide walls get support from adjoining panels and, therefore, their construction should be done continuously.
Stage 2 : Excavation of Trench Panel
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.
Stage 3 : Installation of Stop End Tubes
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.
Stage 4 : Lowering of Reinforcement cage
Reinforcement cage shall then be lowered in the trench panel and suitably supported.
Stage 5 : Placing of Concrete
The concrete cover for the reinforcement shall be maintained by the use of spacers. Boxes or inserts for formation of recesses or for ground anchors shall be lowered along with the case to correct position and levels.
Before placing concrete in the panel the trench shall be flushed properly to clean the bottom and to remove thicker suspension from the lower level.
Stage 6 : Removal Of Stop End Tubes
The stop end tube shall be taken out gradually after initial set of concrete. This may be done carefully with the help of a suitable crane or any other lifting device.
Stage 7 : Successive Panel Construction
Form tube is generally used for creating a joint between primary and secondary panels.
In some cases, semicircular chisels are used instead of form tubes.