考虑剪胀效应的深埋圆形隧道围岩应变软化弹塑性解

隧道围岩非线性体积膨胀影响施工安全,如何正确评价隧道围岩塑性区域内扩容机制非常重要。多数研究从理论上推导深埋圆形隧洞应变软化围岩应力-应变场时仅采用恒定或线性变化剪胀模型,针对此不足,提出了一种基于有限差分法的分析方法,能够合理地考虑围岩非线性剪胀效应及其应变软化特性。利用已有的研究成果,验证了该方法的合理性,并进一步探讨了不同质量石灰岩与支护压力下剪胀系数在围岩塑性区域内的影响因素,比较了恒定与非线性变化剪胀模型下围岩变形的不同。结果表明:对于地质强度指标(GSI)较小、质量较差的岩体,塑性区域内主要由围压控制剪胀效应程度;恒定与非线性变化剪胀模型下围岩洞壁变形差别显著。

Elastoplastic solutions to strain-softening behavior of surrounding rock masses of deep circular tunnels considering dilatancy effect

The nonlinear volumetric increase of rock masses can influence the safety of tunnel excavation; thus it is important to accurately evaluate the dilation mechanism of surrounding rock masses in the plastic zone. However, most of the existing studies solve the stress and strain states in strain-softening rock masses of deep circular tunnels by using the constant or linear dilation model. In order to overcome this deficiency, based on the finite difference method, a new analysis approach is proposed. It can consider the nonlinear dilatancy effect as well as the strain-softening behavior of surrounding rock masses. Moreover, the calculated results are compared with those from other existing methods to verify the calculation accuracy of the proposed method. And then a further study is made to investigate the influence factors of the dilatancy coefficient in the plastic zone with different qualities and support pressures of limestone rock masses, and to compare deformations of surrounding rock masses by the constant and nonlinear dilation models. The results indicate that: for rock masses with lower value of geotechnical strength index (GSI) and poor quality, the confining stress primarily controls the degree of the dilation in the plastic zone; and the deformations at the opening surface with constant and nonlinear dilation models distinguish greatly.