Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation

研究目的:研究弱胶结软岩在应变软化变形阶段的强度参数演化规律。创新要点:针对弱胶结软岩在峰后应变软化变形阶段的刚度劣化和强度衰减的现象,建立考虑刚度损伤劣化的峰后强度参数演化模型。研究方法:首先依据实验结果建立弱胶结软岩的应变软化模型及刚度劣化模型,然后假设岩体后继屈服面均满足Mohr-Coulomb屈服准则,建立考虑峰后刚度劣化行为的强度参数演化规律方程,最后将模型嵌入软件进行数值验证。重要结论:峰后摩擦角演化规律主要由瞬时应力状态和损伤特性所主导,黏聚力除了与应力水平和损伤机制有关外,还与岩体的塑性变形机制有关。所建立的演化模型能较准确地描述弱胶结软岩体的应变软化行为。

To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient co and a softening modulus coefficient a were introduced to take into account the stiff- ness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Molar-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model＇s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength param- eters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confming pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.