The deformation capacity of tunnel will be overestimated by small strain theory especially in high geostress and heavily squeezing rocks, the calculated wall convergence of tunnel may even exceed the excavated radius. Based on the Generalized Zhang-Zhu (GZZ) strength criterion, a new large strain solution for tunnel excavated in strain-softening rocks under high geostress is proposed by a semi-analytical approach. During calculation, the material nodes in the plastic zone of surrounding rock are generated automatically in each unloading step. The locations of these nodes are updated after each step and the governing equations are established on the updated state. The proposed procedure allows one to predict the rock stresses, strains, and deformations in a rational and rigorous manner, and it is validated by numerical simulation. Results show that the ground displacement calculated by proposed approach is in good agreement with that obtained by GeoFBA3D, which indicates that the proposed approach is capable in predicting the large deformation of surrounding rock. As long as the unloading radial pressure of each step δp is sufficient small, i.e., the number of material nodes in the plastic zone exceeds 40, the computational error can be neglected. Compared to HB strength criterion, the GZZ criterion can take into account the intermediate principal stress, which is beneficial to tunnel stability. The applicable conditions for large strain theory and small strain theory are given by parametric studies. Parametric studies show that the calculation error produced by small strain theory can reach 30% when the deformation of surrounding rock exceeds about 10%R₀, therefore, a large strain theory is necessary for calculation.

隧道的变形能力将被小应变理论高估，特别是在高地应力和大挤压岩石中，计算得出的隧道墙收敛甚至可能超过开挖半径。基于所述ģ。广义ž hang- žhu（GZZ）强度准则，通过半解析方法，提出了一种在高地应力下软化岩石开挖隧道的大应变新方法。在计算过程中，在每个卸载步骤中都会自动生成围岩塑性区中的材料节点。这些节点的位置在每个步骤之后进行更新，并且在更新后的状态上建立控制方程式。所提出的程序允许人们以合理而严格的方式预测岩石的应力，应变和变形，并通过数值模拟对其进行了验证。结果表明，所提出的方法与GeoFBA3D计算得到的地位移具有良好的一致性，说明所提出的方法能够预测围岩的大变形。δp足够小，也就是说，塑料区域中的材料节点数超过40，可以忽略计算误差。与HB强度准则相比，GZZ准则可以考虑中间主应力，这有利于隧道的稳定性。参数研究给出了大应变理论和小应变理论的适用条件。参数研究表明，当围岩变形超过R _0的10％左右时，小应变理论产生的计算误差可达30％，因此需要大应变理论进行计算。