砂卵石地层土压盾构掘进掌子面稳定性室内试验与三维离散元仿真研究

采用?800 mm模型土压盾构开展室内掘进试验，以探究砂卵石中土压盾构隧道掌子面失稳诱发地层变形特征。同时，补充开展三维离散元仿真以挖掘室内试验难以获取的掌子面失稳信息，并研究隧道埋深对掌子面稳定性的影响规律。研究结果表明：砂卵石地层中盾构隧道掌子面失稳发展到地表后，沉降曲面呈上大下小逐步收缩的沙漏状，影响范围小于砂土地层。考虑盾构动态掘进过程后，卵石颗粒接触关系变化十分剧烈，掌子面稳定性被削弱，极限支护压力随之增大。掌子面极限支护压力随隧道埋深基本呈线性增加，极限支护压力与初始支护压力之比则随埋深增大而减小。掌子面失稳机制可根据隧道埋深划分为3种模式。与既有研究相比，考虑了盾构动态掘进过程与实际工程更加接近，可为确保砂卵石地层土压盾构隧道施工掌子面稳定提供参考。

Heading stability analysis of EPB shield tunnel in sandy cobble ground using laboratory test and 3D DEM simulation

The ?800 mm model EPB shield machine was used to study the deformation and failure model of earth pressure balance (EPB) shield tunnel in sandy cobble ground. Meanwhile, three dimensional discrete element method (DEM) simulations were conducted to assess the face stability and the influence of buried depth, which couldn’t be observed in laboratory test. Results show that, after tunnel losing stability, the ground settlement surface is “round funnel” shaped with a gradual contraction from top to bottom in sandy cobble ground. The influenced zone is smaller than that of sand. The dynamic soil-cutting process greatly destroys the initial soil fabric, and the face stability is weakened, thus the limit support pressure increases. The limit support pressure increases linearly as buried depth increases, while the ratio of limit support pressure to initial support pressure decreases with increasing buried depth. The face failure mechanism can be divided into three modes according to buried depth. The whole dynamic construction process considered in this paper is close to real constructions, and can serve as guideline for guaranteeing EPB shield tunnel stability in sandy cobble ground.