岩石黏结摩擦特性及非线性强度的指数准则描述

 岩石具有黏结和摩擦特性，但两者在同一位置并不同时存在。裂隙摩擦力随围压增加，达到邻近完整岩石黏结力后将不再滑移引起材料破坏，影响试样强度的裂隙倾角范围随之减小，引起强度非线性增加。主控裂隙引起强度在低围压下线性变化，但不能以Coulomb准则直接确定岩石的内摩擦角。砂岩内存在多种倾角的自然裂隙，引起单轴压缩及低围压的强度离散，围压增高裂隙影响减小，强度随围压规则变化而以指数准则描述；轴向压缩塑性变形引起大理岩黏结力由低向高逐步丧失，而热力损伤引起黏结力整体降低；冻结使岩石黏结力提高而内摩擦角不变。若岩石具有宏观各向同性特征，则常规三轴强度可用指数准则描述，据其确定的初始围压影响系数可估计裂隙摩擦系数；进而理解裂隙对试样强度影响的非线性特征，评价岩石材料的真实黏结力和损伤。

Nonlinear strength of rocks with cohesion and friction using the exponential criterion

The cohesion and friction of rock do not act at the same location simultaneously, therefore，the linear Coulomb criterion does not describe the rock strength accurately. The friction within fissures is related to the confining pressure. A fissure will not slide as the friction approaches the cohesion of intact rock in its neighborhood. And thus，the range of dip angle of fissures affecting the strength of specimen decreases gradually with the increase of confining pressure. The linear variation of the strength under the low confining pressure is usually induced from the fissures with the specific dip angle，and is not applicable to calculate the internal friction coefficient in the Coulomb criterion. The natural fissures with various dip angles in sandstones result in the scattered uniaxial compressive strength under the low confining pressure. The strength varies regularly with the confining pressure，and their relationship can be described with the exponential criterion. The plastic deformation due to the axial compression results in the cohesion losing from low to high in marble specimens，while the thermal damage in marble causes the cohesion losing in full scale. Freezing enhances the cohesion but has no influence on the internal friction. The conventional triaxial strength of macroscopically isotropic rock is perfectly fitted with the exponential criterion，from which the initial influence coefficient of confining pressure on strength is applicable to estimate the friction coefficient of fissures.