The size of plastic zone is an important parameter for determining the surrounding rock stability. In practical engineering, the initial rock environment is dominated by a nonuniform stress field, especially in areas with high tectonic stresses. To explore the plastic zone distribution of the tunnel surrounding rock under a nonuniform stress field, a new analytical solution for the plastic zone radius is proposed, and the reliability of the analytical results is verified with FLAC3D. Moreover, the influence of in situ stress and rock mass parameters on the plastic zone distribution is explored. Finally, the presented solution is verified with several existing engineering cases. The results show that under a nonuniform stress field, the cohesion, friction angle, and vertical stress greatly affect the plastic zone size; the lateral pressure coefficient dominates the plastic zone shape. The average error in determining the size of the plastic zone for the new analytical method is 14.6%, which is 36.1% and 49.9% more accurate than the point criterion method and the stress construction method, respectively. This work could provide a useful reference for predicting the plastic zone distribution and guiding tunnel engineering support with nonuniform stress fields.

塑性区的大小是决定围岩稳定性的重要参数。在实际工程中，初始岩石环境主要是非均匀应力场，特别是在高构造应力区域。为了探究非均匀应力场下隧道围岩塑性区分布情况，提出了一种新的塑性区半径解析解，并利用FLAC3D验证了解析结果的可靠性。此外，还探讨了地应力和岩体参数对塑性区分布的影响。最后，通过多个现有工程案例对所提出的解决方案进行了验证。结果表明，在非均匀应力场下，内聚力、摩擦角和垂直应力对塑性区尺寸影响较大；侧压力系数决定塑性区的形状。新分析方法确定塑性区尺寸的平均误差为14.6%，比点准则法和应力构造法分别准确36.1%和49.9%。该工作可为预测塑性区分布、指导非均匀应力场隧道工程支护提供有益的参考。