Observed Performance of a Deep Multistrutted Excavation in Shanghai Soft Clays

Abstract

A 15.5 m deep multistrutted soft clay excavation of a metro station in Shanghai has been monitored. The deep excavation was supported by a concrete diaphragm wall. The monitoring included wall deflections, surface and subsurface ground settlements, total pressures, and pore-water pressures. Relatively small wall deflections and ground settlements were measured as compared with similar case histories worldwide. The small deflections and settlements observed probably occurred because of the use of a short excavation section, application of compaction grouting for improving ground conditions, and the use of active prestress steel struts. No significant “creep” deflection of the diaphragm wall could be identified over a 60 day concrete curing period. Continuous ground settlements accompanied by the dissipation of pore-water pressures were observed. By using Terzaghi’s one-dimensional consolidation theory, the observed settlements were found to be attributed to the primary consolidation rather than creep effects.