1. Key Laboratory of Energy Engineering Safety and Disaster Mechanics Ministry of Education(Sichuan University),Chengdu　 610065,China; 2. College of Architecture and Environment, Sichuan University, Chengdu 　 610065, China;3. Institute of New Energy and Low-carbon Technology, Sichuan University, Chengdu　 610065,China

为研究页岩在破坏过程中的起裂机制,对具有不同层理倾角的页岩岩样进行了不同围压下的常规三轴压缩实验,基于裂纹体积应变拐点和岩样体积应变拐点分别确定了页岩的起裂应力和裂纹损伤应力。试验结果表明,在相同围压下,层理倾角对页岩岩样的起裂应力大小影响很小,但对裂纹损伤应力的影响较大,这最终导致了页岩破坏模式和破坏强度对层理倾角的依赖性;当层理倾角相同时,随着围压增大,页岩起裂应力与峰值应力的比值变化逐渐增大,而裂纹损伤应力与峰值应力的比值变化很小,说明在层理倾角相同的条件下围压对页岩中裂纹的起裂有显著的影响,而对裂纹的非稳定扩展影响较小;基于断裂力学的压剪裂纹模型解释了页岩的起裂机制,并利用试验数据验证了该模型的合理性;利用该模型预测页岩中含有裂纹的平均长度约为0.985 mm,与现有文献中的结果较吻合;同时该模型的计算结果表明当页岩中的压剪裂纹长度超过3 mm时,裂纹长度对页岩起裂应力的影响不显著。

In order to study the crack initiation mechanism and damage evolution of shale during the rock progressive failure process,some conventional triaxial compression experiments under different confining pressures were conducted by using shale specimens with different bedding plane dip angles. Based on the inflection points of crack volume strain and specimens’ volume strain,the crack initiation stress and crack damage stress were determined respectively. The experiments results indicated that with the constant confining pressure,the inclination of bedding plane had little influ- ence on the crack initiation stress while the dip angle of bedding plane would affect the crack damage stress signifi- cantly,which induced that the failure patterns and strength of shale specimens were depended on the inclination of bedding plane. When the dip angle of bedding plane was same,the ratio of crack initiation stress and rock strength ele- vated with the increase of the confining pressure,but the ratio of crack damage stress and rock strength varied very little. This phenomenon demonstrated that the confining pressure had a significant effect on the crack initiation while had less influence on the crack unstable propagation. The crack initiation mechanism of shale was analyzed based on the compression-shear mixed mode crack in fracture mechanics. The model was verified as reasonable by experimental da- ta. The length of the compression-shear crack was predicted as 0. 985 mm by the presented model,which had a good a- greement with the existing literatures. The numerical results of the model showed that as the length of the compression- shear crack was over 3 mm,the value of crack initiation stress could be seen independent on the crack length.

四川省应用基础研究计划资助项目(2015JY0280)；四川省科技支撑计划资助项目(2012FZ0124)；国家自然科学基金资助项目(41472271)；

Li Cunbao,Xie Heping,Xie Lingzhi. Experimental and theoretical study on the shale crack initiation stress and crack damage stress[ J]. Journal of China Coal Society,2017,42(4):969-976.