三门核电循环水泵房超深基坑支护设计实例

Support of ultra-deep foundation pits of circulating water pump house in Sanmen nuclear power plant

三门核电循环水泵房基坑为超深基坑(最深处为32.3m),处于基岩面埋藏较浅且上部覆盖较厚淤泥层和回填石层的特殊区域。本工程依据地层条件,将基坑边坡划分为完全基岩边坡、基岩埋深浅且无淤泥地层的边坡、基岩埋深较大且有较厚淤泥层的边坡3种类型。分别采用3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,淤泥质软土黏聚力及内摩擦角小,基坑侧壁受水平荷载大、易失稳等难题。典型断面计算结果表明,锚拉力最大为361.84kN;基坑侧壁最大水平位移为19.26mm,支护桩最大正负弯矩值为711.36kN.m和-787.52kN.m,基坑顶部最大沉降量为50mm,均满足设计与规范要求。

The circulating water pump house foundation pit is ultra-deep with the deepest point of 32.3m and is located in a special area where bedrock is shallowly buried and mud and backfill layers in the upper level are deep, so the support requirement for foundation pit is much higher. According to the stratigraphy distribution, three types of side slope of deep foundation pit were divided： complete bedrock, shallowly buried bedrock without sludge layer and deeply buried bedrock with big depth of sludge layer. Three supporting methods were respectively applieated： step-slope excavation for bedrock, 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 coastal soft soil region with the higher ground water level, lower c and φ, easier instability of side of foundation pit due to the great horizontal load. The results of typical section analysis show that the maximum tension of prestressed anchor is 361.84kN, the maximum horizontal displacements is 19.26mm, and the maximum positive and negative bending moment value is 711.36kN·m and -787.52kN·m, which meet the standard and design requirements .