Abstract: The main stress axis rotation caused by the unloading of the shield excavation plane was taken into account in the “wedge-prism” limit equilibrium model. Based on the Casagrande formula, the limit equilibrium solution of the limit support pressure of shield excavation in anisotropic foundation was deduced. Finally, the influence of each calculation parameter on the limit support pressure was analyzed by examples. The results are shown below: the limit supporting pressure of tunnel surface decreases linearly with the increase of the anisotropic ratio k, and it would be unsafe to ignore the anisotropic of strength, especially when the anisotropic ratio k is less than 1; While the k is more than 1, the limit supporting pressure of tunnel face would decrease first with the increase of cover-to-diameter ratio C/D and then tend to be constant contrary to what happened when k is less than 1. Furthermore, the variations of the limit support pressure along with the increase of C/D will be more obvious as the strength of soil shows much more significant anisotropic properties; the limit support pressure of tunnel face decreases linearly along with the increase of cohesion and decreases nonlinearly with the increase of internal friction angle.

Key words: tunnel engineering, tunnel face, limit support pressure, anisotropic, limit equilibrium method

摘要： 将盾构开挖面卸荷引起的主应力轴旋转考虑到“楔形体-棱柱体”极限平衡模型中，基于Casagrande各向异性强度公式，推导得到各向异性 地基中盾构开挖面极限支护压力的极限平衡解，最后结合算例分析了各计算参数对极限支护压力的影响。算例分析表明：盾构开挖面极限支护压 力随各向异性比的增大而线性减小，在各向异性比小于1时，若不考虑土体强度的各向异性会偏于不安全；在各向异性比大于1时，盾构开挖面极 限支护压力随埋深比的增大而先减小后稳定，在各向异性比小于1时，规律则相反，且土体强度各向异性越明显，其变化的幅度越大；盾构开挖面 极限支护压力随土体黏聚力的增大而线性减小，随土体内摩擦角的增大而非线性减小。

关键词: 隧道工程, 盾构开挖面, 极限支护压力, 各向异性, 极限平衡法