考虑吸力历史的陕北黄土干湿循环剪切试验研究

Experimental study on dry wet cyclic shear of loess in northern Shaanxi considering suction history

为研究干湿循环下不同风干饱和度(表征历史最大吸力)对陕北黄土力学特性的影响,开展考虑应力路径的固结不排水三轴试验。试验结果表明:干湿循环作用对黄土的力学特性影响显著,与原始土样(未经历干湿循环)相比,经干湿循环土样在不排水剪切过程中应力—应变曲线由原来的应变硬化型逐渐转变为应变软化型,且随着风干饱和度的降低(历史最大吸力越大),土样初始剪切刚度越大;对于受剪时的孔隙水压力,经干湿循环作用的土样大于原始土样,风干饱和度越低孔隙水压力越大,有效应力越小,有效应力路径曲线朝着偏应力和平均有效应力减小的方向偏移;干湿循环作用对陕北黄土力学特性的影响是由干湿循环引起的塑性体积压缩和微裂隙发展两个方面相互作用的结果。

In order to study the influence of different air drying saturation(representing the historical maximum suction)on the mechanical properties of saturated loess under dry wet cycles,consolidated undrained triaxial tests considering stress path were carried out.The results show that the effect of dry and wet circulation on the mechanical properties of saturated loess is significant.Compared with the original soil sample(without dry wet cycle),the stress-strain curve of the soil sample after dry wet cycle gradually changes from the original strain hardening type to the strain softening type in the undrained shear process,and the initial shear stiffness of the soil sample increases with the decrease of air drying saturation(the greater the historical maximum suction).For the pore water pressure under shear,the soil sample under the action of dry wet cycle is larger than the original soil sample.The lower the air drying saturation is,the greater the pore water pressure is,the smaller the effective stress is,and the effective stress path curve deviates in the direction of decreasing deviatoric stress and average effective stress.The influence of wetting drying cycles on the mechanical properties of saturated loess is the result of the interaction between the plastic volume compression and the development of microcracks.