Field instrumentation has been installed to monitor the behaviour of a T-shaped diaphragm retaining wall founded in overconsolidated clay during and immediately after its construction as part of the Aldershot Road underpass. The construction sequence involved installation of the wall under bentonite followed by excavation below two levels of temporary props and casting of a permanent reinforced concrete prop slab below the final carriageway level. The permanent prop slab was designed to restrict long term swelling pressures of the clay and constructed as a shallow V-shape with hinges at each wall and in the centre. Measurements of ground movements, wall movements and bending moments, temporary and permanent prop loads, and heave pressures and porewater pressures below the carriageway slab were made during the various construction stages. (A)

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