A diaphragm wall (D-wall) is a reinforced concrete structure constructed in situ panel by panel. In the basement market D-walls are often used on congested sites, close to existing structures where the excavation depth and ground conditions would prove problematic for piled walls.
The D-wall construction sequence can be summarised as following:
- Construct guide wall at working platform level – typically two parallel concrete beams to control panel alignment.
- Excavate rectangular panels with rope-suspended mechanical or hydraulically-operated grabs. Where penetration is required through strong rock hydromills, hydraulically operated reverse circulation trench cutters may be adopted.
- Support trench excavation with bentonite or polymer slurry to enable excavation below groundwater table in all ground conditions.
- Install temporary stop ends to form the joints between adjacent panels normally with a water stop included at the joint.
- Place the panel reinforcement cages and tremie the concrete.
Most common applications for D-walls are:
- Deep basements
- Underground carparks and railway stations
- Tunnel approaches
- Underpasses
- Shafts for tunnel ventilation
- Pump stations