承压水位变动下深大基坑空间效应离心试验与数值模拟

基坑工程是典型的三维空间问题，只有在一定条件下才能简化为平面应变问题。针对基坑工程的空间效应问题，首先采用离心模型试验建立基坑工程三维模型，分析承压水位变动条件下基坑变形规律；然后，进一步开展三维数值模拟，与离心模型试验结果进行对比验证，并开展基坑长度、开挖深度、承压水位高度和基坑面积等因素对基坑三维空间效应的影响研究。研究表明：三维基坑离心模型试验监测得到基坑中部和角部断面处的地连墙水平位移以及基坑外侧地表沉降，验证了角隅效应，且承压水位上升时角隅效应更显著；影响因素分析表明，长江I级阶地中当基坑长度大于6倍开挖深度时，基坑中间断面基本为平面应变状态；随开挖深度逐渐增大时平面应变比显著增大，而当深度大于25 m时增大速率减缓；承压水位升高时角隅效应更显著，承压水位超出地表3 m时平面应变比为0.46。该研究成果为长江I阶地典型二元结构地层深大基坑的设计和施工提供依据。

Centrifugal model tests and numerical simulation of three-dimensional space effect of deep and large foundation pit under the confined water level fluctuation

The deformation of foundation pit is considered as a typical three-dimensional (3D) space problem, but it can be simplified as a plane strain problem under specific conditions. Through 3D centrifugal model tests of a foundation pit, the deformation laws of the middle and the corner of the long side of the foundation pit were achieved under the fluctuation of the confined water level. Then 3D numerical simulation was further carried out, and the obtained results were compared with the results from the centrifugal model test. The numerical method was also used to analyse the effects of foundation pit length, excavation depth, confined water level and foundation pit area on the 3D space of foundation pit. The results showed that the corner effect was verified by the horizontal displacements at different sections of the ground wall and the surface settlement outside the foundation pit. When the length of the foundation pit was more than six times the excavation depth in Yangtze River Terrace I, the middle section of the foundation pit was basically in the plane strain state. As the excavation depth increased, the plane strain ratio increased significantly. However, the increase rate slowed down when the depth was greater than 25 m. The corner effect was more obvious with increasing confined water level, and the plane strain ratio reached 0.46 when the level exceeded 3 m. The research results provide the basis for the design and construction of the deep and large foundation pit in the typical binary structure strata of the Yangtze River Terrace I.