真三轴应力条件下钻孔围岩稳定性及塑性区特性

为探究中间主应力对预制孔岩石力学性质的影响,基于自主研发的"多功能真三轴流固耦合试验系统",进行了等b等σ3试验。试验结果表明:主应力方向、中间主应力对岩石变形和强度特性均有较大影响。裂纹特征应力值随中主应力系数b的增加呈现先增大后减小的趋势;裂纹主要在垂直孔轴线方向发育并首先在较小的主应力方向发生破坏。几种条件下试样的强度均随中主应力系数的增大而先增大后减小。其中,最大主应力平行于孔轴线时强度最高,稳定性最好;在中主应力系数b较小时,中间主应力平行于孔轴线时强度最低,而b较大时孔轴线沿最小主应力时强度最低。基于广义平面应变理论,分析了中间主应力对孔周围塑性区的影响。

Stability and plastic zone characteristics of surrounding rock under true triaxial stress conditions

In order to explore the influence of intermediate principal stress on the mechanical properties of prefabricated holes in rock,the authors carried out the constant b and σ3 tests of prefabricated hole in sandstone under true triaxial stress conditions based on the self developed “multi functional true triaxial geophysical (TTG) apparatus”.The experimental results show that the principal stress axis direction and the intermediate principal stress all have great influence on the deformation and strength characteristics of the rock.The crack characteristic stress increases first and then decrease with the increase of the principal stress coefficient b.In addition,the crack develops mainly in the direction of the vertical borehole axis and begins to destroy in the direction of the smaller principal stress.The strength of the specimen increases first and then decreases with the increase of the principal stress coefficient in several test conditions.Among them,the highest strength and the best stability occur when the maximum principal stress is parallel to the borehole axis.The rock strength is the lowest when the intermediate principal stress is parallel to the borehole axis at a smaller value of b.In contrast,the strength is the lowest when the minimum principal stress is parallel to the borehole axis at a larger value of b.Furthermore,the authors analyzed the effects of intermediate principal stress on the plastic zone around the hole based on the generalized plane strain theory.