Characteristics of Excavation-Induced Deformation Associated with Different Propped Retaining Walls in Soft Soil

Abstract

This paper reports the field performance of deep excavation of two subway-station cases, including the lateral wall deflection and the settlements of surrounding soil. The involved retaining structures were contiguous pile wall (CPW), soil-mixing wall (SMW) and diaphragm wall (DW), all embedded in soft clay. The profile of the measured wall deflections showed a typical bulging type at the end of the excavation. The ratios of the measured maximum wall deflection to the excavation depth were found to be similar among the three types of retaining walls. The relationship between the normalized maximum wall deflection and the factor of safety was described. The observed maximum deflections of the retaining walls were generally around the lower bound proposed by existing findings. This may be attributed to the use of prestressed struts and the short horizontal span of the excavation. The measured settlement of ground surface increased linearly with the increasing maximum lateral wall deflection; meanwhile, the magnitude of settlement became extraordinarily large due to the presence of sludgy soil. A concave pattern was proposed for the surface settlement profiles for the three types of retaining walls. The concave-pattern profiles were proposed for the subsurface settlement at the depths of 0, 5 and 10 m while the spandrel-pattern profiles were proposed at the depths of 15, 20 and 25 m. The critical depth derived from the concave-type to the spandrel-type was 63% of the excavation depth. As to the contiguous pile walls and the soil-mixing walls, the scopes of the involved area influenced by excavation were different.