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Diaphragm Walls in Deep Excavations

Diaphragm wall is a continuous underground wall constructed to be used such 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.

Diaphragm wall are constructed in-situ panel by panel and panel width is generally 600 mm -1500 mm. These walls are formed from reinforced concrete and are constructed as normal cast-in-place walls with support, which become part of the main structure. The wall is usually designed to reach very great depth, sometimes up to 50 m, mechanical excavating method is thus employed. Typical sequence of work includes:

  1. Construct the guide wall
  2. Excavation to form the diaphragm wall trench
  3. Support the trench cutting using bentonite slurry
  4. Insert reinforcement and placing of concrete to form the wall panel

Access Engineering pioneered in introducing this technology to Sri Lanka engaging it in the ITC One Hotel & Residencies in Colombo Fort area. Thereafter this technology was utilized in several other project and presently it is used in construction of ODEL Mall for ODEL PLC in Alexandra Place, Colombo 07.

The ODEL Mall consists of 5 basement floors & 8 upper floors. The basement floors are to facilitate the parking requirement while the upper floors are for the shopping complex and residential purposes. Excavation is going up to 15.75 m and the diaphragm wall is embedded up to 24 m from ground level.

Excavation depth

The construction site is in conjunction with the operational car park. Therefore the site has been divided to two parts (Zone A and Zone B) in order to facilitate parking required for the operation of existing ODEL shop. Once the Zone A first temporary support is completed, steel plates are laid on top, making the space usable for parking of vehicles. Meanwhile the parking facility is provided in Zone B.

Divided Two Zones

Temporary supporting work in Zone A

Once the parking facility is allocated in Zone A, and Zone B area excavation and temporary supporting work can be started.

Parking on Zone A area

Basement excavation on progress

Total area of excavation proceeding from the Zone B and Basement floor construction is preceded. Once the construction of building in Zone B area and finishing in Basement floor in Zone B is completed, parking area is shifted to Basement 01 and Basement 02 in Zone B. Then construction of Zone A area will be moved forward and the total building construction will be completed while providing adequate parking facility.

Parking shift to Zone B Basement 01 and 02

Author : Senarath Bandara

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