黏土盾构隧道开挖面被动破坏研究

盾构隧道施工中控制合理的开挖面支护压力是维持开挖面稳定安全的关键。为了研究黏土盾构隧道开挖面被动破坏的机理,通过采用考虑分段掘进和开挖卸荷引起土体强度折减的模拟方法分析黏土隧道开挖面由于支护压力过大引起的前部土体被动破坏模式、塑性区发展及相应地层位移,并探究隧道埋深、直径、土体性质等因素对开挖面被动极限支护压力的影响规律,结合离心模型试验确定开挖面被动极限支护压力合理控制范围。结果表明:①当开挖面支护压力逐步增大时,前部土体受挤压呈现铲形位移破坏模式,同时由于冲切作用在开挖面周围形成环状塑性区,开挖面前部纵向土体位移随着到开挖面距离的增加总体呈现先增大后减小至稳定的趋势,深层断面横向土体位移则近似符合正态分布曲线形式;②埋深和直径增大会不同程度地引起极限支护压力增大,土体性质对被动极限支护压力影响的敏感程度依次为弹性模量、内摩擦角、泊松比和黏聚力,建议被动极限支护压力控制范围为1~1.9倍的静止土压力。研究成果可供黏土盾构隧道施工控制参考。

Passive Failure of Excavation Face by Shield Tunnelling in Clay Strata

Reasonable support pressure on excavation face is the key to maintaining the tunnel face stable and safe during shield tunnelling construction. In this study, the passive failure mode of excavation face in clay strata, the plastic zone development, and the stratum displacement caused by excessive support pressure are simulated numerically in consideration of soil strength reduction induced by segmented advancing and excavation unloading. In addition, the influences of tunnel depth, tunnel diameter, and soil properties on the limit support pressure are explored. The reasonable range of limit support pressure is given through centrifugal model test. Results are concluded as follows: 1) When support pressure intensifies gradually, the front soil is squeezed into a shovel shape, and in the meantime, a ring plastic zone is formed around the excavation face due to punching and cutting effect. With the distance to excavation surface prolongs, the longitudinal strata displacement in front of excavation face increases but then decreases until stabilizes; whereas the horizontal strata displacement in the deep follows normal distribution.2) The augment of tunnel depth and tunnel diameter would amplify the limit support pressure to different extends. Support pressure is most sensitive to elastic modulus, followed by internal friction angle, Poisson’s ratio and cohesion. The range of passive limit support pressure is recommended to be 1-1.9 times of earth pressure at rest. The results would offer reference for shield tunneling construction control in clay stratum.