修正Hoek-Brown准则的等效Mohr-Coulomb强度参数确定方法研究

Study on determination method of equivalent Mohr-Coulomb strength parameters of a modified Hoek-Brown failure criterion

合理确定岩石材料强度参数是工程设计的关键问题之一。为有效描述岩石的强度特性,众多学者提出了大量三维强度准则,其中基于两参数偏函数的修正Hoek-Brown(H-B)准则取得了良好效果,能够有效地反映岩石的静水压力效应、Lode角效应及中间主应力效应等强度特性。确定修正H-B准则的等效Mohr-Coulomb(M-C)参数有利于提高其在工程应用中的便利性,因此提出一种基于I1-√J2平面计算三维强度准则瞬时等效M-C参数的方法,应用于修正H-B准则,并对计算方法的合理性及瞬时等效M-C参数与岩石强度特性的关系进行讨论。结果表明:瞬时等效M-C参数可有效表征非线性静水压力效应,且合理反映Lode角效应和中间主应力效应的区间性特点;瞬时等效M-C参数可有效表征静水压力对Lode角效应的影响和最小主应力对中间主应力效应的影响,静水压力增大时,Lode角效应更为明显,且当最小主应力增大时,瞬时等效内聚力反映出更为显著的中间主应力效应;该方法能够合理地计算瞬时等效M-C参数,修正H-B准则具有准确预测岩石强度的能力。上述成果对修正H-B准则在实际工程中的应用具有较强的指导意义。

The Mohr-Coulomb(M-C) failure criterion has been widely used in engineering practice, which does not efficiently reflect the rock strength characteristics including the hydrostatic pressure effect, Lode angle effect and intermediate principal stress effect. To overcome this weakness, attempts have been made to develop the three-dimensional failure criteria, among which a recently proposed modified Hoke-Brown(H-B) failure criterion based on a two-parameter deviatoric function has an excellent performance. However, the M-C failure criterion is still widely used in practice. In order to avoid the difficulty resulting from the use of three-dimensional failure criterions in engineering, a new approach is proposed to determine the equivalent M-C strength parameters from the three-dimensional modified H-B failure criterion. The procedure for determining the equivalent M-C strength parameters from the modified H-B criterion is demonstrated in detail, and the equivalent M-C strength parameters influenced by the rock strength characteristics are investigated. Results show that dependence of M-C strength parameters on the hydrostatic pressure effect is nonlinear, and the effect of the intermediate principal stress and Lode angle is related to observation range. For a higher hydrostatic pressure, Lode angle has greater influence on the equivalent M-C strength parameters. As the minimum principal stress rises, the effect of intermediate principal stress on instantaneous cohesion is more significant. Verification of this determination method is conducted based on the true triaxial test data of different rock types, demonstrating its applicability. Findings in this paper have significant sense for practical application of the modified H-B failure criterion in the rock engineering.