滨海软土区深基坑支护结构设计及变形分析

Structural Design and Deformation Analysis of Deep Foundation Pit in Marine Soft Soil Region

基于三门核电站一期泵房深基坑工程的成功实践,对滨海软土区的基坑工程特点、支护结构设计和变形特点进行了详细分析。本工程依据地层条件,将基坑边坡划分为完全基岩边坡,基岩埋深小、无淤泥地层的边坡,基岩埋深较大、有较厚淤泥层的边坡三种类型,并分别采用了三种支护型式:放坡、排桩+岩锚、排桩+深搅重力墙+岩锚,有效解决了滨海软土区的地下水位高,淤泥粘聚力及内摩擦角小,基坑侧壁受水平荷载大、易失稳等难题。现场监测结果表明锚索应力及基坑的水平位移和沉降均满足规范及设计要求。三门核电站泵房深基坑支护所面临的岩土工程问题对于沿海工程具有一定的普遍性,该方案的成功应用可为沿海地区类似工程的设计提供参考。

Based on the successful engineering,practice in the deep foundation pit excavation on supporting system of pump house for first-stage Sanmen nuclear power station, in order to choose the optimum supporting structure scheme for the deep foundation pit with the deepest point of 32.3m, the characteristics of project, supporting structural design and deformation analysis in the marine soft soil region were analyzed in this paper. According to the stratigraphy of the project site, we divided the side slope of deep foundation pit into three types ： complete bedrock, shallowly buried bedrock without sludge layer and deeply buried bedrock with thick sludge layer. And three supporting methods were respectively applied for this project： step-slope excavation, piles in row and prestressed anchor cables, and the combination of piles in row and cement-soil wall and prestressed anchor cables, which effectively solved the difficult problem in marine soft soil region with the higher ground water level, lower inner friction angle （ φ ） and cohesion （ c ）, and easier instability of side of foundation pit due to the great horizontal load. By means of in-situ monitoring, a conclusion is drawn that the tension of prestressed anchor, excavation deformation and settlement meet the standard and design requirements. The geotechnical engineering problems that the pump house of first-stage Sanmen nuclear power station faced are common to costal projects, and the successful application of our supporting project can provide guidance for similar projects.