新建地铁车站零距离下穿既有地铁区间隧道施工过程中，基坑的增层开挖导致既有桩基侧摩阻力下降，从而对桩基的承载力产生不利影响。目前，新建地铁车站增层开挖施工作用下既有桩基侧摩阻力的计算理论尚不成熟。针对这一工程问题，本文以深圳地铁13号线公明广场站零距离下穿既有六号线项目为背景，采用Mindlin应力解推导增层开挖卸荷作用下既有桩基桩侧摩阻力的计算公式，对新建地铁车站增层开挖过程中既有桩基侧摩阻力的变化规律开展研究。通过与数值模拟结果进行对比，验证了理论计算方法的正确性，在此基础上获得了参数变化对桩侧摩阻力和卸荷应力的影响规律。研究结果表明：既有桩侧摩阻力随增层开挖深度的增大而减小，侧壁卸荷应力与总卸荷应力比值随增层开挖深度的增大而增大；桩侧摩阻力随增层开挖面积的增大而增大，侧壁卸荷应力与总卸荷应力比值随增层开挖面积的增大而减小。在开挖深度较深，开挖面积较小或考虑边桩侧摩阻力时，需考虑侧壁卸荷应力的影响。

During the construction of a new subway station beneath an existing running tunnel, the shaft resistance of the existing pile induced by the excavation may decrease and the bearing capacity of the pile may be affected. Presently, the computation theory of the shaft resistance for the existing pile induced by the excavation is not clear. Taking Shenzhen Metro Line 13 Gongming Square Station to cross the existing Line 6 project at zero distance as the background, the calculation formula of shaft resistance of pile induced by excavation under existing building is obtained by using the Mindlin stress solution. By comparing with the numerical simulation results, the correctness of the Mindlin stress solution is proved. The influence of parameter changes on shaft resistance of pile and unloading stress is analyzed. The results show that: when the depth of excavation increases, the total shaft resistance of pile decreases, and the ratio of side wall unloading stress to total unloading stress increases; when the excavation area increases, the total shaft resistance of pile increases, the ratio of side wall unloading stress to total unloading stress decreases. Therefore, when the excavation depth is deep, the excavation area is small, or the shaft resistance of side pile is considered, the influence of the side wall unloading stress needs to be considered.

国家自然科学基金项目（面上项目，重点项目，重大项目）