Behaviour during construction of a propped diaphragm wall in stiff clay at Walthamstow

Embedded retaining walls of the bored pile or diaphragm wall type are being increasingly used for below ground construction particularly in the London area for North Circular Road Improvement Schemes. One of these schemes (Chingford Road to Hale End Road) included the construction of an underpass and involved the installation of counterforted diaphragm retaining walls embedded in over-consolidated clay to a depth of 23m. Excavation between the walls of the underpass took place beneath temporary props with the finished structure being permanently propped below the carriageway using an innovative hinged design. This report describes the field instrumentation and monitoring carried out to establish the behaviour of the structure and the adjoining ground during each stage of construction and in the longer term. Measurements of ground movements, total lateral stresses and porewater pressures, together with wall movements and bending moments were carried out. (A)