中间主应力对砂岩扩容及强度特性影响

基于自主研发的多功能真三轴流固耦合试验系统,进行了真三轴应力(σ1﹥σ2﹥σ3)条件下,保持体应力不变、改变中主应力系数的砂岩强度试验,探讨了不同中主应力系数条件下砂岩的变形、强度及剪切破坏特性。试验结果表明:在真三轴应力条件下,扩容起点随中主应力系数b的增大而呈递减趋势。应力加载过程中扩容存在明显的阶段性:随最大主应力的增加,稳定压缩段,体应变近似呈线性递增趋势;加速扩容段,体应变近似呈二次函数增大,且应变速率呈线性增大。保持体应力不变条件下,砂岩峰值强度随中主应力系数b的增大而逐渐降低,符合修正Lade准则。试验应力条件下,岩样主要发生双斜面对称剪切破坏,剪切破坏面倾角随b的增加呈线性增大。

Influence of intermediate principal stress on dilation and strength characteristics of sandstone

Based on the self made “multi functional true triaxial fluid solid coupling experiment system”,an experiment to investigate the strength of sandstone under true triaxial compression（σ1﹥σ2﹥σ3）for different coefficients of the intermediate principal stress and maintaining the volume stress unchanged was carried out.The authors have discussed the deformation,strength and shear failure plane feature of sandstone under different coefficients of intermediate principal stress.The research result shows that the starting point of dilatancy decreases with the increase of the coefficient b of intermediate principal stress under true triaxial compression.The dilatancy exists an obvious stage under experimental conditions,with the increase of maximum principal stress,the volume strain increases linearly at the steady compressing stage and increases as a quadratic function at the accelerating stage with the strain rate increases linearly.The strength of sandstone decreases with the coefficient b increase and coincides with the Modified Lade Criterion under the condition of keeping volume stress unchanged.In this experimental test,the rock specimens generally developed a typical type of symmetrical double shear failure and the angle of shear plane increases linearly with the coefficient b increase.