基坑开挖过程中软土性状若干问题的分析

通过对基坑工程中主动区和被动区土体的应力路径、应力状态、土的不排水抗剪强度和孔隙水压力变化规律的讨论，几个模糊概念得到澄清．研究表明：基坑开挖过程中无论主动区还是被动区都处于卸荷状态；土体抗剪强度在不同区域、不同加载阶段是不同的．在同一固结压力下，不排水抗剪强度是卸荷抗剪强度的2倍．在模拟基坑工程应力路径的三轴室内试验研究基础上，发展了一个孔隙水压力公式．根据常规三轴试验得到的抗剪强度和孔隙水压力系数变化规律可确定不同应力路径下的土体抗剪强度．

Analysis of soft clay during excavation

According to the discussion about stress paths, stress states, undrained shear strength and the law of change of pore water pressure in active and passive zone of foundation pit, several fuzzy concepts are clarified. The research idicates: states of decompression appear in both active and passive zone during excavation; shear strength id different in different zones and loading stages. Under the same consolidation pressure, undrained shear strength is two times of decompression shear strength. A formulation is developed on basis of laboratory triaxial shear test simulating the stress paths of foundation pit excavation. The soil's shear strength through different stress paths can be decided according to the laws of change of pore water pressure coefficient and shear strength, which are got from the routine triaxial test.