对与基坑工程有关的一些规范的讨论(2)

Discussion on some codes concerned with building foundation pit (Part 2)

本文是对与基坑有关的规范系列讨论的第二部分,结合基坑工程土的应力路径问题讨论了不同强度指标与计算方法的适用性。针对目前勘察报告对于一层土只给出一个或一组强度指标的情况,指出了应重视取样及现场测试深度的问题;认为对于支挡结构前后土体应进行不同围压的三轴试验;讨论了基坑工程中墙前后土体的应力路径与室内试验应力路径的区别,讨论了应力路径对于不同强度指标以及水土压力计算的影响。并特别指出,支挡结构物前、后土体的平均主应力或者某些方向的主应力常常是减少的,对于饱和黏性土的固结不排水三轴试验,可能产生负的超静孔隙水压力,从而会影响土的抗剪强度指标。

This is the second part of a series of discussion papers. Through the research of the stress path of soil on both sides of retaining structure, the applicability of strength parameters and calculation methods are discussed. It is pointed that the depth of the sampling and field test of soil is important for strength parameters used in the calculation of earth pressure. In the triaxial tests of the soil in front and behind of retaining structure, different confining pressures are necessary. In the behind of wall, the vertical stress （maximum principal stress） is constant and the lateral stress （minor principal stress） decreases continuously, and that is the same as the RTC test （reduced triaxial compression test） and different from the CTC test （conventional triaxial compression test）. In pit engineering, the decrease of principal stress results in the negative excess hydrostatic pore water pressure and the increase of shear strength.