Analysis on the Collapse Causes of Foundation Pit under Complex Environmental in Soft Soil Areas

The thesis takes a foundation pit project, which is located in the Hangzhou-Jiaxing-Huzhou alluvial plain area of Zhejiang Province, having deep soft soil within the depth range affected by excavation and is under complex environment that is adjacent to existing buildings and significant pipelines, as its research object, and respectively conducts inspection and investigation on the aspects of its engineering geological conditions, the current status of the support structure after collapse, the construction quality of the support structure, and technical data, by combining the calculation and numerical analysis on the support structure and components. It then draws the conclusion that the reasons of the foundation pit collapse are that the selection and layout of the support structure for the external corner at the design phase are unreasonable, the soil layer parameters and the value selection of "m value" are unreasonable, and along with the partial over excavation of the foundation pit and the construction quality defects of the support structure of the foundation pit. At the last part of the thesis, it proposes reinforcement plans and design and construction suggestions for the foundation pit in soft soil areas with complex environmental conditions, which provides reference for the design and construction of foundation pits in similar regions with homogeneous environmental conditions in the future.