局部承载黏土地层浅埋隧道稳定机制的连续上界极限分析

针对局部承载黏土地层浅埋隧道施工的横断面稳定机制问题，采用上界极限分析理论和基于Peck公式及不排水不可压缩条件的地层位移模式，分别计算研究了地层物理力学参数、浅基础荷载参数、桩基础荷载参数对隧道必要支护压力下确界的影响。在其他参数不变的前提下，隧道必要支护力下确界随地层抗剪强度的增大而线性地减小，随地层重度的增大而线性地增大；随浅基础荷载量值的增大而线性地增大，随浅基础荷载横向距离的增大而非线性地减小并趋于定值，随浅基础荷载横向范围的增大而非线性地增大并趋于定值；随桩基础侧面剪力荷载量值、底面压力荷载量值的增大而线性地增大，随桩基础荷载横向距离的增大而非线性地减小并趋于定值；对端承桩而言，当桩基长度小于（或大于）地层沉降竖向分布曲线极大值点对应的深度时，随桩基长度的增大而非线性地增大（或减小）。

Continuous upper bound limit analysis for the stability mechanism of shallow tunnels in locally loaded clay soils

With regard to the issue of transverse stability mechanism of shallow tunnel constructions in clayey grounds with local loads, an upper bound limit analysis theory and a continuous soil movement model based on Peck’s formula and undrained incompressible condition are employed to computationally study the effects of soil physical-mechanical parameters, shallow foundation loads, and pile foundation loads on the infimums of the necessary tunnel support pressures. It is found that, while keeping other parameters constant, the infimum support pressure decreases linearly with the increase of the shear strength of soil, and increases linearly with the increase of the unit weight of soil; increases linearly with the increase of the magnitude of shallow foundation loads, decreases nonlinearly with the increase of the transverse distance of shallow foundation loads and approaches asymptotically to a constant, and increases nonlinearly with the increase of the lateral range of shallow foundation loads and approaches asymptotically to a constant; increases linearly with the magnitudes of the shear load on pile shaft and the pressure load at the pile end, decreases nonlinearly with the transverse distance of the pile foundation loads and approaches asymptotically to constant, and for end-bearing piles, increases (or decreases) with the length of pile when the latter is smaller (or larger) than the depth where the largest settlement in the vertical distribution occurs.