突变地质界面盾构隧道开挖面极限支护压力研究

Study on Limit Support Pressure of Shield Tunnel Excavation Face with Mutational Geological Interface

盾构隧道穿越由岩质到富水软黏土或砂土的突变地质界面时,受不均匀土压力、强弱介质力学性质差异、孔隙水压力剧变等因素影响,将产生沿弱体界面的滑移破坏。基于筒仓理论,建立突变地质界面下的梯形棱柱体极限平衡模型,推导开挖面极限支护压力计算公式;以济南轨道交通R1线隧道下穿腊山河段为工程背景,分析不同界面距离时开挖面的破坏模式和围岩变形分布特征,揭示开挖面极限支护压力随界面距离的变化规律。研究结果表明:不同梯形体长度比下的极限破裂角均相同,可近似为45°-φ/2;当界面距离比ε为-1≤ε≤0时,开挖面的破坏模式由楔形体转化为梯形体,其极限支护应力比随界面距离的减小而显著增大;开挖面极限支护压力随界面前后黏聚力、内摩擦角差异的增大而增大,界面倾斜时对围岩稳定性的影响比界面垂直时更加显著。

Due to the mutual influence of uneven earth pressure,the difference in mechanical properties between strong and weak media and the drastic change of pore water pressure,sliding failure would occur along the weak geological interface with shield tunnel passing through the mutational geological medium of rock and water-rich soft clay or sand.Based on silo theory,trapezoid-prism limit equilibrium model under mutational geological interface was put forward,and calculation formulas for the limit support pressure of excavation face were derived.In the engineering background of Jinan rail transit line R1 tunnel passing through Lashan river,the failure modes of excavation face and the deformation distribution characteristics of surrounding rock under different interface distances were analyzed,and the change laws of the limit support pressure with interface distance were revealed.Results show that all the limit rupture angles are the same under different length ratios of trapezoid body,and can be approximated as 45°-φ/2.When the range of interface distance ratio is-1≤ε≤0,the failure mode of excavation face transforms from wedge into trapezoid body,causing its limit support stress ratio to increase significantly with the decrease of interface distance.The limit support pressure of excavation face increases with the increase of cohesive strength and internal friction angle gap on both sides of interface.The influence of inclined geological interface on surrounding rock stability is more significant than that of vertical interface.