考虑渗透系数各向异性的盾构隧道开挖面稳定性数值极限分析

Computational Limit Analysis of Shield Tunnel Face with a Consideration of Permeability Anisotropy

城市地铁隧道普遍采用盾构法施工,盾构掘进过程中密封舱支护力不足会引起开挖面的突然坍塌,造成重大人员伤亡和财产损失。隧道开挖会造成周围地层水力环境改变,引起地下水渗流,不仅在开挖面前方土体中产生渗透力,也使得围岩力学性质弱化,大大增加了盾构隧道开挖面失稳的风险。现有工作一般假定土体渗透系数为各向同性以简化计算,然而,土在沉积的过程中由于各种因素的影响会产生各向异性,即渗透特性与所选取的方向有关。基于极限分析理论,结合有限元四面体单元和半正定锥规划,建立三维数值极限分析方法。在此基础上,结合渗流分析,研究渗透系数各向异性条件下盾构隧道开挖面附近渗流场及开挖面极限支护力的变化规律,分析渗透系数比对开挖面破坏模式的影响,为盾构隧道安全施工提供重要的参考。

The shield method is widely applied in the construction of subways and instability of the excavated surface of shield tunnels will be induced if insufficient support pressure is exerted,resulting in significant economic losses and casualties.The hydraulic states will be changed by the excavation and the induced water flow not only introduces the seepage force but also deteriorates the mechanical behavior of the surrounding soils.Therefore,more attention should be paid to the stability of the tunnel face under seepage conditions.The permeability of the surrounding soils is mostly simplified to be isotropic,which is in fact anisotropic due to the effect of the depositional environments.Based on the bounding theory,a three-dimensional computational limit analysis method is established by the combination of the simplex strain finite element method and the semi-definite programming.Through the incorporation of seepage analysis,the effect of permeability anisotropy on the seepage field,the limit supporting pressure and the collapse mechanism of the shield tunnel face is discussed.The present paper can provide important guidance to the construction of shield tunnels.