流塑淤泥地层深基坑钢板桩围堰位移突变原因分析及处理

广东省珠海市洪鹤大桥主墩承台位于珠江西江流域的流塑状淤泥地层，采用钢板桩围堰进行基坑支护，基坑开挖过程中，钢板桩围堰发生较大的变形。经详细分析，发现导致事故的主要原因有地下水位持续升高导致土体力学性能显著下降、边跨侧钢板桩长度不足、基坑边缘集中荷载过大、施工控制不严、内支撑体系施工精度不足等。为了确保深基坑支护的安全，在全面分析总结了钢板桩围堰变形原因的基础上，结合实际情况，采取了增设穿透淤泥质土层的钢管桩围堰、加强内支撑体系等加固处理措施，并在实施过程中进行持续监测，最终安全地完成了基坑工程的施工。

Causes and treatment of displacement of the deep foundation pit sheet pile cofferdam in flow-plastic silt stratum

The main pier cap of Zhuhai Honghe Bridge is located in the flow silt area of the Xijiang River Basin of the Pearl River, and the steel sheet pile cofferdam is used for the foundation pit support. During the excavation of the foundation pit, the steel sheet pile cofferdam was obviously deformed. After detailed analysis, it was found that the main causes for the accident were significant decrease in the mechanical properties of soil due to continuous rise of the groundwater level, insufficient length of the steel sheet pile in the side span, excessive concentrated load on the edge of the foundation pit, and insufficient construction accuracy of the support system. In order to ensure the safety of deep foundation pit support, the reinforcement measures for the steel sheet pile cofferdam were adopted in regard to the actual condition through comprehensive analysis of the causes for the deformation of the steel sheet pile cofferdam, including extension of the steel pipe pile cofferdam into the muddy soil laye, strengthening of the internal support system, which were continuous monitored during the construction process. Finally, the foundation pit construction was completed safely.