不同应力路径下饱和重塑黄土的力学特性

Mechanical properties of saturated remolded loess under different stress paths

土体的力学特性往往因应力状态和应力路径而异。为了探讨垂直加载和等剪路径下饱和土的力学特性,制备饱和重塑黄土试样,通过固结不排水(CU)和常剪应力排水剪(CSD)三轴试验,分别测定并绘制其应力-应变曲线、孔隙水压力变化曲线和应力路径曲线。试验结果表明,饱和重塑黄土在2种路径下有明显不同的变形特点:CU路径下的应力-应变曲线皆呈弱软化型,孔隙水压力先快速上升后逐渐趋于稳定;CSD路径下维持偏应力为一常量,施加孔隙水压力后的很长时间内试样变形很小,当孔隙水压力增大至试验围压的60%~75%时,试样迅速破坏。CSD路径无偏应力峰值,文中根据轴应变随平均有效应力变化曲线定义了等效峰值破坏线。通过对比发现,2种路径下饱和重塑黄土的有效峰值强度指标差异明显,而有效残余强度指标相近,表明有效残余强度指标是重塑黄土内在属性,受应力路径的影响不大。该研究结果可为实际工程选取正确的应力路径试验提供参考。

The mechanical properties of soil often vary with stress state and stress paths. In order to investigate the mechanical properties of saturated soil under vertical loading and constant shear stress path, saturated remolded loess samples are prepared. Through consolidated undrained(CU) triaxial tests and constant shear stress drained(CSD) triaxial tests, the corresponding stress-strain curves, pore water pressure curves and stress path curves are measured. The results show that the saturated remolded loess has obviously different deformation characteristics under the two paths. In CU tests, the stress-strain curves are softening weakly. The pore water pressure rises rapidly and tends to be stable gradually. In CSD tests, the deviator stress is a constant and the pore water pressure is applied. The deformation of samples is small for a long time at the beginning. When the pore water pressure increases to 60%-75% of the confining pressure, the samples are destroyed rapidly. Because there is no peak value of deviator stress in CSD path, the equivalent peak failure line is defined according to the axial strain-mean effective stress curves. By comparison, it is found that the effective peak strength indexes of the saturated remolded loess are significantly different under the two paths. However, the effective residual strength indexes are similar, indicating that the effective residual strength indexes are the internal attribute of the remolded loess and are not affected by the stress path. This study can provide reference for selecting the correct stress path test in practical engineering.