非饱和砂土有效应力增量的试验研究

Testing Investigation on Effective Stress Increment of Unsaturated Sandy Soils

为了解土层有效应力增量对地基沉降的贡献程度,进行了非饱和砂土在不同轴向荷载和围压作用下的饱和试验、静载试验和莫尔-库伦应力分析,得到了砾砂土和圆砾土在饱和状态下的天然重度、黏聚力及内摩擦角等主要物理力学指标,利用这些指标计算得到有效应力增量值及其沉降贡献量.试验结果表明:与砾砂相比较,圆砾土的饱和度更易达到100%,其饱和重度较砾砂大,孔隙率和含水量却较砾砂小.对于饱和砂土,由有效应力法计算出来的主应力值大于由总应力法计算出来的主应力值,所得内摩擦角和黏聚力比用总应力法得出的结果更加合理.另外,有效应力增量对基底沉降的贡献不可忽略.

In order to investigate the vertical deformation contributed by effective stress increment of soils overlying foundation base, the saturation test of unsaturated sandy soil and the static load test were conducted with different axial loads and cell pressures, and work of calculation and analysis based on Mohr-Coulomb＇＇s method was finished.The main physical and mechanical indexes of gravelly sand and gravel, such as natural gravity, cohesion and angle of internal friction etc., were obtained under condition of saturation.Effective stress increment and its vertical deformation were obtained by using the indexes.The results indicate that degree of saturation of gravel is more easily to reach 100% compared with gravelly sand, and saturated unit weight of gravel is larger, but porosity and water content of gravel are smaller than that of gravelly sand.As to saturated sandy soil, the principal stress computed by effective stress method is usually larger than that by total stress method, thus angle of internal friction and cohesion obtained by effective stress method are more reasonable.In addition, vertical deformation contributed by effective stress increment can not be ignored.