软弱岩石峰后应变软化力学特性研究

 软弱岩石给采矿工程中巷道支护和维护带来一系列棘手的问题，深入研究软弱岩石受力变形、破坏的机制和规律，对于保证巷道围岩的安全和稳定具有十分重要的意义。通过对软弱泥岩进行常规三轴压缩试验，得到不同围压下的全应力–应变关系曲线，然后依据峰后岩石任意一点应力状态均满足Mohr-Coulomb极限破坏条件的假设，建立以广义黏聚力 和广义内摩擦角 两个状态参数来表征的软弱岩石后继屈服面模型。在此基础上，利用试验数据绘制岩石峰后不同软化状态时的几组莫尔应力圆，通过“切线法”得出莫尔强度包络线的拟合方程，进而确定出不同围压条件下的 和 值，并借助Matlab软件对广义黏聚力 、广义内摩擦角 与等效塑性剪切应变、围压之间的关系进行最小二乘曲面拟合，得出软弱岩石峰后力学参数的软化规律，结果表明：随着围压的增加，广义黏聚力 值呈快速增加的趋势，而广义内摩擦角 值则显著减小；广义黏聚力 受岩石软化程度的影响也十分明显，从岩石峰值状态到残余状态 值迅速降低，平均降低53.88%，而广义内摩擦角 值在该软化过程中则基本保持稳定。最后，将得到的广义黏聚力 和广义内摩擦角 的拟合方程嵌入到FLAC内置应变软化本构关系中，并利用FLAC3D软件对模型的正确性进行数值模拟验证，结果表明数值模拟曲线与试验曲线比较吻合。

POST-PEAK STRAIN SOFTENING MECHANICAL PROPERTIES OF WEAK ROCK

Weak rock brings about a series of difficult issues to tunnel support and maintenance in mining engineering. Further study of the mechanism and law of weak rock deformation and breakage has great significance to the safety and stability of the tunnel wall rock. Based on the conventional triaxial compression test of weak mudstone,complete stress-strain curves under different confining pressures are obtained. Then based on the assumption that the stress state at a point satisfies Mohr-Coulomb critical failure criterion,building the weak rock subsequent yielding plane model characterized by generalized cohesion (-c) and generalized internal friction angle (-φ) using the test data,several Mohr's stress circles of post-peak rock at different softening conditions are drawn;then using tangent method to build the fitting equation of Mohr's strength envelope curve,(-c) and (-φ) under different confining pressures could be determined. And by means of Matlab software,the relationship between generalized cohesion (-c),generalized internal friction angle,equivalent plastic shear strain and confining pressure are fitted by using least square surface. Through the relationship,the post-peak mechanical parameters softening law of weak rock can be obtained. The results show that with the increase of confining pressure,generalized cohesion (-c) shows a rapid increase trend;but generalized internal friction (-φ) angle(-φ) decreases significantly;and the influence that the softening condition brings to the generalized cohesion is evident;the generalized cohesion (-c)has a rapid decrease when the stress state changes from the peak value state to the residual state;the average of the decrease is 53.88%,while generalized internal friction angle almost maintains stable during the change of the softening condition. At last,the fitting equations of generalized cohesion and generalized internal friction angle(-φ) are embedded into the strain softening constitutive relation of the fast Lagrangian analysis of continua in 3 dimensions(FLAC~(3D));and using FLAC~(3D) software,numerical verification is made to the model. The results show that the numerical simulation curves agree well with the test curves comparatively.