为求解发生大变形时软弱围岩圆形隧洞的应力和位移，基于三剪应力统一强度理论和拉格朗日坐标下的对数应变，通过考虑施工期、运行期和检修期3种工况下主应力顺序以及渗流等影响，推导理想弹塑性模型软弱围岩的弹塑性解，并分析弹性模量、泊松比、孔隙水压力和强度准则4个参数对塑性区厚度和洞壁处径向位移的影响。研究结果表明： 1）施工期围岩塑性区厚度随弹性模量的增大呈现先增大后逐渐趋于一个稳定值（小应变解），而运行期围岩塑性区厚度随弹性模量的增大呈现逐渐减小后逐渐趋于一个稳定值（小应变解），洞壁处径向位移在施工期和运行期2种工况下均随弹性模量的增大逐渐减小； 2）施工期和运行期围岩塑性区厚度随泊松比增大几乎无影响，而洞壁处径向位移随泊松比增大呈线性增大； 3）施工期围岩塑性区厚度和洞壁处径向位移随孔隙水压力的增大而增大，而运行期围岩塑性区厚度和洞壁处径向位移随孔隙水压力的增大而减小； 4）不同强度准则下的塑性区厚度和洞壁处径向位移变化显著； 5）检修期围岩塑性区厚度和洞壁处径向位移变化规律与施工期类似。对于发生大变形的软弱围岩圆形隧洞，推导的弹塑性解与小应变解明显不同。

 To calculate the stress and displacement of a circular tunnel in soft surrounding rock during large deformation, the elastoplastic solution of the ideal elastoplastic model for soft surrounding rock is derived using the unified strength theory of triple shear stress and logarithmic strain in Lagrangian coordinates considering the influence of principal stress sequence and seepage under three working conditions of construction, operation, and maintenance periods. Then, the effects of elastic modulus, Poisson′s ratio, pore water pressure, and strength criterion on plastic zone thickness and radial displacement of the tunnel wall are analyzed. The results reveal the following: (1) With an increase in elastic modulus, the plastic zone thickness of the surrounding rock during the construction period increases gradually and stabilizes at a certain value (small strain solution), and during the operation period, it decreases gradually and stabilizes at a certain value (small strain solution); whereas the radial displacement of the tunnel wall during construction and operation periods decreases with an increase in elastic modulus. (2) The Poisson′s ratio has little impact on the plastic zone thickness of the surrounding rock during construction and operation periods, whereas the radial displacement of the tunnel wall increases linearly with an increase in Poisson′s ratio. (3) With an increase in pore water pressure, the plastic zone thickness of the surrounding rock and the radial displacement of the tunnel wall during the construction period increase, whereas during the operation period, they decrease. (4) The plastic zone thickness and the radial displacement of the tunnel wall vary significantly under various strength criteria. (5) The variations in the plastic zone thickness and the radial displacement of the tunnel wall during the maintenance period are similar to those observed during the construction period. However, for the circular tunnel with large deformation in soft surrounding rock, the derived elastoplastic solution clearly differs from the small strain solution.