盾构掘进过程中隧道上覆地层松动土压力研究

针对盾构法隧道施工过程中如何合理地确定上覆地层松动土压力问题，提出基于极限分析理论的松动土压力计算方法。研究地层发生主动失稳时的破坏模式，假设地层为服从莫尔-库仑屈服准则的理想弹塑性体，构建由多刚性滑块构成的失稳破坏模型，考虑了黏聚力、地表超载和岩土重力对地层稳定性的影响，建立松动土压力极限分析模型。算例分析表明：在大埋深情况下，极限分析模型的计算结果与离心模型试验和数值模拟的结果相接近，计算精度优于传统的太沙基理论，合理地反映了土层拱效应作用。计算结果也表明：受土层拱效应影响，松动土压力同隧道埋深成正比，并趋于稳定值，计算精度也随着埋深的增大而提高；松动土压力与砂土内摩擦角成反比，且内摩擦角越大计算精度越高。

Study on Loosening Earth Pressure in Sandy Ground for Shield Tunneling

In shield tunneling, it is very critical to estimate the loosening earth pressure reasonably for preventing ground instability and controlling shield’s driving force effectively. However, due to the influence of ground property, overburden depth and geometric construction parameters, the ground behavior is extremely complicated. Comparing with the limit equilibrium method, the theoretical basis of the limit analysis theory is more rigorous. Therefore, the loosening earth pressure of shield-driven circular tunnels is investigated by an upper bound approach in limit analysis, and the Mohr-Coulomb failure criterion is adopted. Furthermore, a multi-blocks failure mechanism is developed for loosening earth pressure in sandy ground. The basic examples are carried out, and the results are examined by comparing with Terzaghi theory, numerical simulation and centrifugal tests. It is confirmed that the proposed model predicts the loosening earth pressure reasonably well at the case of large overburden depth, and shown that the overburden depth and friction angle are the important factors affecting the loosening earth pressure.