For environmental reasons highways within built-up areas are increasingly being constructed below ground in retained cutting using bored pile or diaphragm retaining walls. Wall penetration, and hence costs, can often be reduced by using permanent prop slabs for support at carriageway level. However little guidance is available on the design of such structures particularly when they are founded in stiff clays where high insitu lateral stresses can produce high structural loadings on both the wall and propping system. This report describes the field instrumentation and monitoring carried out to establish the behaviour of a propped secant bored pile wall under construction at Hackney. Measurements of movements, total lateral stress and porewater pressures were carried out in the ground. The movements and bending moments developed in the wall and the loads in the permanent prop were also monitored. (A)

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