考虑围压影响的深埋圆隧围岩应变软化与剪胀特性分析

 不同围压下岩石应变软化与剪胀特性不同，若在隧洞开挖中考虑围岩塑性区域内变化围压影响，其应力–应变场求解方式将区别于既有文献中的传统方法。根据围压影响下应变软化围岩的临界塑性剪切应变变化特征，给出改进的判断围岩是否进入塑性残余区域的规则；引入考虑围压与临界塑性剪切应变的非线性剪胀模型。基于Hoek-Brown屈服准则，根据一定径向应力增量将围岩塑性软化与残余区域分层，采用有限差分法对围岩应力–应变场进行求解；为分析围压对围岩稳定性的影响，根据临界塑性剪切应变与剪胀系数变化与否，设定4种非线性力学模型，深入分析并比较4种力学模型下临界塑性剪切应变、剪胀系数与围岩变形等在塑性软化与残余区域的分布规律。研究结果表明：地质强度指标GSI较小时，考虑围压影响下的围岩应力–应变场与未考虑时差异明显；此时临界塑性剪切应变的减小对开挖边界的围岩剪胀性具一定抑制作用。

ANALYSIS OF STRAIN-SOFTENING AND DILATANCY BEHAVIORS OF ROCK MASSES IN DEEP CIRCULAR TUNNEL CONSIDERING CONFINING PRESSURE

Rocks exhibit different strain-softening and dilatancy behaviors under various confining pressures. For tunnel excavation，the method to obtain the stress and strain states considering variability of the confining pressure in the plastic zone is different from those in the existing studies. According to the variation of critical plastic shear strain of the strain-softening rock mass influenced by the confining pressure，a modified criterion was presented to determine whether the rock mass resides within the plastic residual zone. A nonlinear dilatancy model was introduced to account for the confining pressure and the critical plastic shear strain. The plastic softening and residual zones were divided according to a certain radial stress increment. The stress and strain components are obtained based on Hoek-Brown failure criterion with the finite difference method. In order to discuss the influence of the confining pressure on the rock mass stability，four nonlinear mechanical models were established according to whether the critical shear strain or dilatancy coefficient was changed or not. The critical plastic shear strain，the dilatancy coefficient and the rock mass deformation in the plastic softening and residual zones were further studied under the four models. The calculated results show that for lower geological strength index(GSI)，the stress and strain states considering the confining pressure distinguish greatly from those not considering it. A reduction of the critical plastic shear strain restrains the dilatancy behaviour of surrounding rock mass near the opening surface to a certain extent.