Ground deformations and soil-structure interaction of a multi-propped excavation in Shanghai soft clays

Ground deformations and soil-structure interaction were monitored at a comprehensively instrumented diaphragm wall panel constructed at a greenfield site. The diaphragm wall retains a 14.5 m deep multi-propped excavation in soft clays in Shanghai, P. R. China. At this greenfield site, the maximum ground surface settlement (delta(v-max)) at the end of excavation ranged from 0.25% to 0.32% of the final excavation depth (He), and the influence zone of ground surface settlement was more than 2.5H(e) behind the wall. Both the measured delta(v-max) and the influence zone of ground settlements at this site are generally larger than for excavations in other, more densely built areas of Shanghai. Force and moment equilibrium analyses of the instrumented panel validate the reliability of the measured earth pressures and prop forces. The measured prop loads from this greenfield site are generally larger than those reported from similar excavations in Shanghai. Earth pressure measurements reveal that concreting of the diaphragm wall panel increased the lateral earth pressure coefficients at the soil/wall interface by a factor of more than 1.4. The stress paths for the retained soil within the propped region generally moved towards the passive state during the last few stages of main excavation, and soil near the formation level approached the passive failure state prior to the completion of excavation.