DIAPHRAGM WALLS
Diaphragm Wall [ DW ] is a technology carried by Foundation Specialists.
Diaphragm Wall can be used as retaining structure, in which case it will also be called “ Cast In Place Reinforced Concrete Diaphragm Wall “, it is a “Top-Down Construction Technology” employed for Excavation Support in difficult soil conditions or whenever excavation has to be carried out in an environment where zero disturbance of the surroundings, including avoidance of water table lowering, and/or zero settlement of neighboring structures are a requirement. Prior to start the execution of DW, it is necessary to survey the DW position and install "Guide Walls" which will guide the DW equipment to the correct aligned position , will prevent the top soil to collapse into the DW excavation, will support the reinforcing bar cages during installation and throughout concrete pouring and Diaphragm Wall is put in place using a segmental installation technique, [generating Reinforced Concrete D W Panels of predetermined dimensions] purposely and specifically designed for each soil formation and particular site requirements, in order to avoid any disturbance and subsidence to the surrounding areas. In cohesionless soil formations under the water-table, the segmental excavation is generally carried out using bentonite suspension as the drilling fluid, in order to balance the action of the water-table and to maintain the excavation perfectly stable until each single “ Panel ” is cast with concrete. Once all the segments or “ Panels “ are cast, they are connected at the top by a reinforced concrete continuous beam [ Coping ], after which, removal of soil on the excavation side can proceed, protected by the Diaphragm Wall. The Diaphragm Wall, depending upon depth of excavation and upon design loads to be applied on the “ earth side “ can be designed to act as a cantilever or as an anchored retaining structure, in this last case, soil or rock anchors shall be drilled, installed and generally post tensioned, at one or more levels (as per design), when excavation reaches the required elevation. Diaphragm walls are used as the perimeter structural walls of building basements, can be properly reinforced to act as the buildings' shear walls. Buildings' columns can be integrated within the diaphragm walls, dowell bars for any application can be attached to the diaphragm wall reinforcing cage prior to installation and in situ casting. Diaphragm wall technology was used by Foundation Specialists to design and construct the Marginal Wharfs of the very large deep water port facilities of the National Steel Corporation. A very large number of Deep Underground Parking Facilities and Deep Underground Building Basements, Steel Mills Pits, Underground Pumping Stations, have been built by Foundation Specialists using the Top-Down Construction Sequence, by constructing Perimeter Walls, including Shear Walls and Columns with Diaphragm Wall Technology, prior to main deep excavation. Diaphragm Wall is sometime called Slurry Wall. An other type of Diaphragm Wall carried by Foundation Specialists is a Technology called Cut-Off Wall or Self-Hardening Plastic Cut-off Wall . The Cut-Off Wall is a continuous and impermeable Diaphragm Wall, generally made using a mix of Cement Bentonite, designed to remain indefinitely, both sufficiently plastic and totally impervious. Plastic in order to follow soil movement and deformation without cracking, totally impervious, including to aggressive fluids, in order to prevent the escape of lechates from the confined areas. Cut-Off Walls are employed whenever there is a requirement for isolating a source of pollution from the surrounding water table, e.g. around Sanitary Landfills or other sources of polluting lechates. The same equipment and basic technology used to execute Diaphragm Wall are employed to install Barrettes or Barrette-Piles, large reinforced concrete piles with a rectangular section or other shapes.