Ground response during diaphragm wall installation in clay: Centrifuge model tests

A series of centrifuge model tests has been carried out to investigate the ground movements which occur during the installation of diaphragm walls in clay soils. The paper describes the centrifuge modelling technique, with reference to features such as the high initial in situ lateral earth pressures in overconsolidated clay deposits, and the stress and drainage boundary conditions imposed at the interface between the trench and the soil. The changes in pore water pressure and ground movements observed during the simulation of slurry trenching and concreting in a number of centrifuge model tests are described, and the influence of ground-water level and trench geometry is discussed. Ground movements were found to depend on a number of factors, including the initial groundwater level and the geometry (length/depth ratio) of the panel. The initial groundwater level is particularly important: soil surface settlements were reduced by a factor of 10 when a plane strain excavation was carried out with the water-table 10 m below ground level rather than at the soil surface. For a diaphragm wall trench 18 . 5 m deep and 1 m wide, three-dimensional effects were found to reduce the displacements at the centre-line of a single panel by a factor of 3 (compared with the plane strain case) for a panel 5 m long, but the benefit for a panel 10 m long was much smaller.