基于三轴极限峰值偏应力的岩石非线性破坏强度准则

A nonlinear failure strength criterion for rocks based on the peak value of deviatoric stress from triaxial tests

  • 摘要: 根据岩石三轴试验强度的变化规律,提出了一种基于三轴极限峰值偏应力的岩石非线性破坏强度准则。将本文强度准则的预测值与15种岩石的三轴试验强度值进行对比,得到的平均绝对误差为2.964%,所有15种岩石的相关性系数均大于0.96,说明本文强度准则具有普遍的适用性,能够较好地预测不同岩石类型的强度。通过与几种典型强度准则的比较发现,本文准则的预测精度略优于目前岩石力学界认为较好的指数型准则,要远好于Hoek-Brown(H-B)准则以及基于临界状态改进的Hoek-Brown(MH-B)准则和改进的Mohr-Coulomb(MM-C)准则。本文准则克服了高围压下H-B准则的预测值与试验强度偏差较大的局限性,避免了MH-B和MM-C准则在围压达到临界围压后不再随围压变化的缺陷。另外,基于应力空间建立了岩石的瞬时黏聚力和内摩擦角与本文强度准则参数kam之间的关系,岩石的瞬时黏聚力随围压的增加而增大,并最终增加到0.5(k+1)σc; 岩石的瞬时内摩擦角随着围压的增加而减小,并逐渐减小到0; 内摩擦角减小到0的同时黏聚力增加到最大值0.5(k+1)σc。本文强度准则中岩石的三轴极限峰值偏应力取决于参数k和单轴抗压强度σc,岩石三轴剪切强度随围压在初始段的增大幅度取决于参数am; 参数km的取值范围较大,其中k> 0,m> 1.0; 而a为< 1.0的正值,取值范围相对集中,为了便于计算可取a=0.95。

     

    Abstract: According to the shear strength of rock variation with confining pressure obtained by triaxial tests, a new non-linear failure strength criterion for intact rock is developed on the basis of the peak value of deviatoric stress.Compared to the test data of 15 kinds of rocks, the average absolute error is only 2.964% by this strength criterion.All the regression coefficient R2 of this strength criterion are larger than 0.96 for the No.1-15 rock.It shows that this strength criterion can well predict the triaxial test strength for different types of rocks with a universal applicability.This strength criterion has a slightly higher predicting accuracy than the exponential criterion regarded as an outstanding criterion in rock engineering.The predicting accuracy of this strength criterion is higher than Hoek-Brown (H-B) criterion, modified Hoek-Brown (MH-B) criterion and modified Mohr-Coulomb MM-Ccriterion.This criterion overcomes the limitations of the H-B criterion with larger deviation comparing with test data under higher confining pressure, and avoids the defect that MH-B criterion and MM-C criterion hold a constant after the confining pressure reaching uniaxial compressive strength σc.In addition, the relationship is established between the parameters of this criterion (k, a and m) and the parameters of Mohr-Coulomb criterion (cohesion c and internal friction angle φ).The instantaneous cohesion of rock increas with confining pressure, and finally increases to 0.5(k+1)σc.The instantaneous internal friction angle decreas as confining pressure increases, and gradually decreases to zero.The internal friction angle decreases to zero while the cohesion increases to the maximum value of 0.5(k+1)σc.For this strength criterion, the maximum value of rock deviatoric stress depends on the parameter k and uniaxial compressive strengthσc, and the increase magnitude of rock triaxial strength with confining pressure at initial section depends on the parameters value of a and m.Both parameters k and m have larger range of values, where k > 0 and m > 1.0.The value a is greater than 0 and less than 1.0, which is relatively centralized.In order to be convenient for calculation, a=0.95 is feasible.

     

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