土压平衡盾构掘进对上软下硬地层扰动研究

 采用Ф800 mm模型盾构开展室内掘进试验以研究土压盾构掘进对上软下硬地层的扰动特征，试验充分考虑土压盾构动态施工全过程的影响。建立与室内掘进试验对应的离散元模型定量分析软土超挖现象并挖掘其他地层扰动信息。研究结果表明：土压盾构在硬岩地层中掘进时地表沉降曲面呈现向软土侧展开的“扇面”状；进入上软下硬地层后地表沉降值与范围均急剧增加，沉降曲面呈现自上而下逐渐收缩的“漏斗”状，硬岩侧收缩速度快于软土侧；上软下硬地层地表位移小于均质软土地层，而地中沉降显著大于后者；上软下硬地层地中沉降槽宽度参数沿深度方向呈指数增加，硬岩占断面比例越小，地中沉降槽宽度参数越大。相同埋深条件下，上软下硬地层地中沉降槽宽度参数小于均质软土地层。硬岩占断面比例越大，渣土中砂土所占比例与相应理论值差异越明显。地表水平位移在竖向沉降槽曲线反弯点处最大。研究可为土压盾构在上软下硬地层施工提供参考。

Soil disturbance induced by EPB shield tunnelling in upper-soft and lower-hard ground

The EPB shield model of Ф800 mm was used in laboratory test to study the soil disturbance induced by the shield tunneling in the upper-soft and lower-hard ground. The corresponding model of discrete element method (DEM) was established to investigate the over excavation quantitatively and other information about the disturbed ground. When tunneling is in the hard rock, the settlement surface is sector shaped，orienting towards the soft soil. When tunneling is in the soft soil, the settlement surface is funnel shaped. The surface settlement of the upper-soft and lower-hard ground is smaller than that of homogeneous soft soil，while the subsurface settlement is much larger than that of soft soil. The width parameter of subsurface settlement trough K increases exponentially along the gravitational direction，and the width parameter gets larger as the ratio of hard rock to whole tunnel face gets smaller. For the same depth，K of the upper-soft and lower-hard ground is smaller than that of the homogeneous soil. The larger proportion of hard rock the tunnel face has，the proportion of the excavated soft soil contained in the muck differs more from its theoretical value. The maximum horizontal displacement occurs at the point of inflection of vertical settlement trough.