不同应力路径下砂岩真三轴试验及数值模拟

True triaxial test and numerical simulation of sandstone in different stress paths

利用TRW-3000室内真三轴试验系统开展不同应力路径下的真三轴加载、卸载试验,研究其相应的力学特性,在此基础上开展PFC^(3D)数值模拟对比试验,探讨细观裂纹演化规律。研究结果表明:岩石最大、最小主应力差(σ_(1)−σ_(3))与中间主应力σ_(2)呈线性相关;基于Drucker−Prager准则拟合不同应力路径下岩石强度效果良好;与加载相比,卸载条件下岩石黏聚力c、内摩擦角φ均有所降低;PFC^(3D)数值模拟试验破坏模式与室内试验破坏模式基本吻合;在不同应力路径下,数值模型剪切裂纹数与拉伸裂纹数均随ε_(1)增大而增大,剪切裂纹比例曲线ε_(1)随变化趋势呈“И”型,且当主应变ε_(1)相同时,随着中间主应力σ_(2)增大,各类裂纹数量减少;与加载相比,卸载时各类裂纹数量快速增加,剪切裂纹数占比降低,曲线由加载的“上凸”型转变为卸载的“下凹”型。

TRW-3000 indoor true triaxial test system was used to carry out true triaxial loading and unloading tests in different stress paths to study the corresponding mechanical characteristics of the sandstone.On this basis,PFC3D numerical simulation comparison test was carried out to explore the evolution law of microscopic cracks.The results show that the difference(σ_(1)−σ_(3))between the maximum and the minimum principal stress of the rock is linearly related to the intermediate principal stressσ2.The Drucker-Prager criterion has good effect in fitting rock strength in different stress paths.Compared to load path,the cohesion c and the internal friction angleφof the rock are reduced under unloading conditions.The results of PFC^(3D) numerical simulation experiment are consistent with those of laboratory experiment.In different stress paths,the numbers of shear cracks and tensile cracks of the numerical model increase with the increase of the maximum principal strainε_(1).Shear crack ratio curve with the maximum principal strainε_(1) trends show"И"type.Under the same maximum principal strainε_(1),with the increase of the intermediate principal stressσ_(2),the numbers of all kinds of cracks decrease.Compared with loading,the number of various cracks increases rapidly and the proportion of shear cracks decreases.The curve changes from"upward convex"type under loading to"downward concave"type under unloading.