基质吸力对灰岩区滑带土强度影响的试验分析

基质吸力是非饱和土中水-土耦合作用的重要力学参数,对于研究非饱和土抗剪强度、降雨或库水位变化诱发的滑坡稳定性具有重要意义。为了探究降雨诱发的基质吸力变化对灰岩区滑带土的影响,通过标准应力途径三轴试验系统,对4组不同基质吸力条件下、3组不同净围压下的试样进行试验,分析得到基质吸力与最大剪应力的关系曲线、应变与剪应力的关系曲线、净围压与剪应力的关系曲线,采用非饱和土双应力变量强度理论进行分析。结果表明:相同基质吸力条件下,剪应力随着剪应变的增加呈现快速增长和缓慢增长2个阶段,其界限点在剪应变10%处;在相同围压条件和非饱和条件下,剪应力随着基质吸力的增加而增加;总黏聚力与基质吸力呈线性关系,其增长斜率夹角即基质吸力相关角为15.5°;当基质吸力为0,30,60,90 kPa时,其总黏聚力分别为22.7,33.4,43.8,46.9 kPa,内摩擦角分别为21.8°,23.6°,26.2°,24.5°。根据Fredlund和Ralaadjo非饱和土双应力强度理论,提出了该滑坡滑带土的抗剪强度修正公式,研究成果可为非饱和土抗剪强度的进一步研究提供参考。

Experimental Study on Effect of Matric Suction on Strength of Slip Soil in Limestone Zone

As an important mechanical parameter of the water-soil interaction in unsaturated soil, matric suction is of great significance for researching the shear strength of unsaturated soil and the stability of landslides induced by changes in rainfall or reservoir water level. In this research, the effect of rainfall-induced change in matric suction on the slip soil in limestone zone was examined via GDS triaxial test system with standard stress path. Matric suction was set different at four values and net confining pressure three levels. The curves of matric suction versus maximum shear stress, strain versus shear stress, and net confining pressure versus shear stress were obtained and further analyzed using the variable double stress principle of unsaturated soil strength theory. Results evinced that under the same matric suction condition, shear strength increased rapidly with the climbing of confining pressure at first and when shear strain reached 10%, such increase attenuated. Under the same confining pressure and unsaturated conditions, shear stress rose with the increase of matric suction. Total cohesive force is in a linear relation with matric suction. The slope of this linear relation, which also equals the related angle of matric suction, is 15.5°. When matric suction is 0 kPa, 30 kPa, 60 kPa and 90 kPa, respectively, the total cohesive force is 22.7 kPa, 33.4 kPa, 43.8 kPa, and 46.9 kPa, respectively, and the corresponding internal friction angle is 21.8°, 23.6°, 26.2°, and 24.5°. According to Fredlund and Ralaadjo's double stress strength theory of unsaturated soil, a modified formula for the shear strength of the slip soil of the studied landslide is proposed for reference.