Performance of Two Propped Diaphragm Walls in Stiff Residual Soils

Diaphragm walls with thicknesses ranging from 600-1,200 mm are increasingly used as both temporary and permanent supports for excavations in congested urban areas. This paper describes the performance of two propped excavations supported by diaphragm walls in stiff residual soils in Singapore. Performance measures include lateral wall deflections and wall-bending moments reduced from wall-inclinometer readings. A method of back-analyzing bending moments in a diaphragm wall from measured wall-inclinometer data for an uncracked and a cracked wall section is also presented and discussed. The finite element method was used for back-analyzing the performance of the two case histories. A series of parametric studies were also performed to study the effects of wall stiffness, wall embedment depth, and prop stiffness on the performance of diaphragm walls for excavations in stiff residual soils. Back-analysis indicated that cracking was accompanied by a substantial reduction in the bending moment in the diaphragm wall and a small increase in the lateral wall deflection.