针对Mogi-Coulomb 强度准则是否适用于三轴卸荷试验,基于已有常规三轴及真三轴的试验数据,利用Mogi-Coulomb强度准则,对常规三轴卸荷及真三轴卸荷条件下的实验数据进行拟合和分析,并对拟合得到的相关强度参数和试样的破坏特征进行分析。结果表明,Mogi-Coulomb 强度准则在常规三轴卸荷条件下有着良好的适用性,而在真三轴卸荷条件下,虽然线性拟合效果较好,但拟合参数反映的岩石黏聚力值出现负数的异常情况。分析现有实验测试结果,可以推测出现参数异常的原因,应是岩石在真三轴卸荷条件下的破坏模式由剪切型破坏转变为强烈的张拉型岩爆破坏所致。这表明Mogi-Coulomb 强度准则虽能在一定程度上反映真三轴卸荷的主应力关系,但其本质仍为基于剪切破坏的强度准则,存在一定的局限性,对于张拉为主-剪切共存型的岩爆破坏,有必要建立一种新的岩石强度准则来反映真三轴卸荷下的岩石本构关系。
To testify the Mogi-Coulomb criterion in triaxial unloading test and based on available unloading testing data, the Mogi-Coulomb strength criterion with a linear fitting method was used in the conventional triaxial unloading tests and the true triaxial unloading tests, respectively. A comprehensive comparative analysis was presented for the related strength parameters according to the fitting results and combination of the failure characteristics of rock specimens. The results showed that the Mogi-Coulomb strength criterion has a good applicability to rock samples under conventional triaxial unloading conditions. However, under true triaxial unloading tests, even though the fitting degree is very good, the fitting parameter a is negative which leads to a negative cohesion of rock samples. This is impossible in practice. Since the Mogi-Coulomb strength criterion is based on the assumption that rock fails in shear, it cannot describe the failure of rock under true triaxial unloading conditions in which the failure modes of rocks specimens may change from shear to extensional slabbing or rock burst. Therefore, for combined shear and tensile failure processes of rocks under true triaxial unloading conditions, it is necessary to build a new strength criterion to describe its constitutive relationships, which is important for deep rock mechanics.
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