考虑应变率效应的广义Hoek-Brown动态强度准则

Generalized Hoek-Brown dynamic strength criterion incorporating strain rate effect

岩石强度特性具有明显的围压效应和应变率效应,研究复杂应力状态下动态强度准则对于岩石动力学分析至关重要。利用10^(-5)~10^(2.32) s^(-1)应变率范围内砂岩静动态间接拉伸和单、三轴压缩强度试验数据,进行了广义Hoek-Brown强度准则预测砂岩动态强度的适用性研究,分析了材料参数的应变率效应。结果表明,广义Hoek-Brown强度准则能够较好地描述同一应变率下较低拉应力区到较高压应力区砂岩强度规律,低应变率区单轴抗压强度c_s和参数a变化不大,高应变率区随应变率的增加非线性增大,而参数m几乎不受应变率影响。基于分析建立了单轴抗压强度c_s和参数a的应变率效应函数关系,提出了由低应变率到高应变率下的广义Hoek-Brown动态强度准则统一表达式,进一步探讨了岩石强度依赖应变率效应和围压效应的物理机制。

The mechanical behavior of rock material is strongly influenced by confining pressure and strain rate. It is of great significance to establish a unified strength criterion taking account of complex stress state and strain rate in the rock dynamics analysis. A series of strength data obtained from uniaxial compression test, triaxial compression test, Brazilian test on sandstone under strain rates of 10^(-5)-10^(2.32) s^(-1), are applied to assess the applicability of generalized Hoek-Brown strength criterion and to analyze the strain rate effect on the material parameters. The results show that the strength rule of sandstone can be reasonably described by the generalized Hoek-Brown strength criterion from low tensile stress region to relatively high compressive stress region under the same strain rate. The parameters both uniaxial compressive strength c_s and parameter a show a slight increase at lower strain rate, and show a dramatically nonlinear increase at higher strain rate, whereas parameter m almost does not change with different strain rates. Therefore, the function relationships between the material parameters c_s and a of the generalized Hoek-Brown dynamic strength criterion and strain rate can be established. On this basis, a new generalized Hoek-Brown dynamic strength criterion is proposed taking account of strain rate from the region of 10^(-5)-10^(2.32) s^(-1). The physical mechanisms of strain rate and confining pressure effects on dynamic strength of sandstone are further studied.