Study on the deformation of a deep metro excavation under complex environment

A 15.5-m-deep multi-strutted metro excavation in Shanghai soft clays was monitored.It was found that relatively small wall deflections and ground settlements were measured as compared with similar case histories worldwide,and no significant space effect existed.The reason was probably because of the use of short excavation section,application of compaction grouting for improving ground conditions and the use of active pre-stress steel struts based on the theory of time-space effect.Based on soil volume change and square root time method,time-dependant soil deformation was studied during curing period of middle-slab concrete.It was pointed out that the settlement was attributed to the primary consolidation as well as creep effects.