为研究中间主应力在圆形隧道围岩承载力所发挥的作用,根据统一强度理论和塑性增量的非相关性流动法则,提出了考虑中间主应力影响的应变软化围岩特征曲线的有限差分计算方法,并通过实例验证该方法的正确性。由于围岩的力学模型对特征曲线的影响较大,采用3种不同力学模型——弹塑性模型、弹脆性模型和应变软化模型,分别研究了中间主应力和支护力对圆形隧道围岩塑性区半径,应力分布和隧道洞壁处位移的影响。结果表明:当围岩采用弹塑性模型时,计算的塑性区半径和洞壁处的位移均较小,没有考虑岩体强度在塑性区的弱化,建议慎重选择;中间主应力对塑性区半径和洞壁处的位移发展均有抑制作用,特别是在无支护状态下弹脆性模型的抑制作用最显著;中间主应力对塑性发展的抑制作用随着支护力的增加而减小;弹塑性交界处围压,应变软化模型下软化区与残余区交界面的围压均与支护力无关,且随中间主应力影响系数的增加而减小。

To study the role of the intermediate stress on the bearing capacity in a circular tunnel,a finite difference method,which is used to calculate the strain-softening behavior of rock masses considering the effect of the intermedi- ate stress,is proposed based on unified failure criterion and non-flow associated flue. The accuracy of the proposed method is investigated by example verification. Due to the significant effect of mechanics model on the ground response curve,three different mechanics models,i. e. ,elastic-perfect plastic model ( EPP ),brittle plastic model ( BP ) and strain-softening model (SS),are used to study the effect of intermediate stress and support force on the plastic radius, the stress distribution in the plastic zone and the displacement at the tunnel wall,respectively. The results show that the plastic radius and the displacement at the tunnel wall calculated by EPP are much less than those by other me- chanic models. Therefore, the EPP is suggested to be cautiously used because it does not consider the weakening strength of rock masses in the plastic zone. The intermediate stress can restrain the development of the plastic radius and the displacement at the tunnel wall,especially for EB under no support force condition. This restraining effect of the intermediate stress on the plastic development decreases with the increase of support force. The confining stresses on the boundary of elastic-plastic zone and the boundary of softening-residual zone are not related to support force at the tunnel wall,but decrease with the increase of intermediate stress coefficient.