指数型岩石真三轴强度准则

岩石强度是工程岩体稳定性评价和结构优化设计的前提和基础,通过岩石真三轴试验分析了岩石强度演变特征:(1)随着最小主应力的增加,岩石强度逐渐增大,但增幅逐渐减小并趋于零;(2)岩石广义压拉强度比随静水压力的增大呈先增大再减小的规律,并最终趋于1,即在π平面上呈三角形向圆形转变的过程;(3)岩石强度随中间主应力增大表现为先增大再减小的过程。三参数型指数函数完全符合岩石强度在子午面上的基本特点,而L_(WW),L_(MN)和L_(YMH) 3个罗德函数准确反映了中间主应力对岩石强度的影响,且无条件满足拉压子午面区间光滑、连续、外凸性要求。利用π平面广义拉压强度比和罗德函数将指数型拉压子午面结合,构建了指数型真三轴强度准则,分析了强度参数对岩石强度的影响及其空间包络特征。最后采用14种岩石的真三轴试验数据对指数型真三轴强度准则进行了最优拟合误差分析,结果表明指数型真三轴强度准则均具有良好的拟合精度,可正确描述软–硬不同性质岩石的强度特征。

Exponential true triaxial strength criteria for rock

The rock strength is the premise and foundation for stability evaluation of rock engineering and optimization design of structures. Based on the true triaxial test results, the evolution of rock strength are analyzed: (1) The rock strength increases with the minimum principal stress, however, its increasing amplitude gradually decreases and trends to be zero; (2) The ratio of generalized compression to the extension strength firstly increases then decreases, and finally tends to be one with the increasing minimum principal stress. The envelope of strength criteria on deviatoric plane varies from approximate triangle to circular; (3) During the process of the intermediate principal stress increasing from the minimum principal stress to the maximum one, the rock strength firstly increases and then decreases. The exponential function with three parameters satisfies the basic characteristics of rock strength on the meridian plane. And the Lode dependence functions of L_WW, L_MN and L_YMH well reflect the effect of the intermediate principal stress, and unconditionally satisfy the smooth, continuous and convex requirements. Then the exponential true triaxial strength criteria are proposed by combining the extension and compression meridian curves with the selected lode dependence functions. The influences of strength parameters and space characteristics are further analyzed. Finally, fourteen types of rock true triaxial test data are employed to validate the proposed criteria. The results show that the proposed exponential true triaxial strength criteria are of good accuray in predicting rock strength, and can well reflect different types of rock ranged from soft to hard.