南京某风井深基坑工程地下连续墙跨越软弱高层压水粉砂夹层，成槽施工时软弱夹层容易出现局部失稳，进而发生塌孔或缩孔并影响施工安全。为探明地下连续墙成槽过程局部失稳机理，分析并评价软弱夹层处的地下连续墙成槽质量，确定满足槽壁稳定性要求的泥浆最优配比，采用考虑土拱效应的局部失稳破坏体三维计算模型计算槽壁局部稳定性安全系数，并通过超声波监测和现场成槽试验验证计算结果。结果表明：破坏体三维计算模型可以有效评价具体工程软弱夹层处的槽壁局部稳定性；槽壁后方土拱高度与槽段长度和土体内摩擦角成正相关；增大泥浆重度并提高泥浆液面高度有助于增大槽壁局部稳定性安全系数；成槽作业时选用优化后的泥浆配比可以满足实际工程经济性和安全性要求，槽壁整体稳定性系数和局部稳定性系数可分别提高为1.5和1.25。研究成果可为实际工程中地下连续墙成槽稳定性和经济性设计提供参考。

A diaphragm wall is used in a deep foundation pit project in Nanjing that crosses a soft high-level pressurized water-sand interlayer. This weak interlayer is recognized as prone to local instability during trenching, which can result in collapse or shrinkage and compromise construction safety. To investigate the local instability mechanism of the diaphragm wall during trenching, a three-dimensional computational model was established by considering soil arch effects. The local stability safety factor of the trench wall was computed. Ultrasonic monitoring and on-site trenching tests were carried out to validate the calculation results. The results show that this three-dimensional model effectively evaluates the local stability of the trench wall at the weak interlayer. The soil arch height behind the trench wall is positively correlated with trench length and soil friction angle. Increasing the mud density and raising the mud level improves the local stability safety factor. An optimized mud ratio satisfies both economic and safety requirements, and raises the overall stability coefficient and the local stability coefficient of the trench wall to 1.5 and 1.25, respectively. The research findings provide a reference for designing stable and economical diaphragm wall trenching in similar engineering projects.