渗流条件下曲线盾构隧道开挖面稳定性分析

Stability Analysis on Curved Shield Tunnel Excavation Face Under Seepage

为研究渗流条件下曲线盾构隧道开挖面稳定性,在筒仓理论和极限平衡法的基础上,对传统楔形体模型进行改进,建立了斜梯台-楔形棱柱体模型,推导出受渗流作用影响的浅埋曲线盾构隧道开挖面极限支护力的解析式,通过数值模拟及工程实例对模型结果进行了验证,并进行了参数影响分析。研究发现:在渗流条件作用下,渗流力构成了浅埋盾构隧道开挖面极限支护力的重要部分,本工程地质情况下,渗流力最高可占极限支护力的46%,且渗流力受地下水位的影响较大。本研究模型理论计算结果与数值模拟结果较为接近且误差在5%以内,证明本研究所提出的三维计算模型的合理性,实际施工中为保障工程安全,盾构隧道实际支护力大于极限支护力理论值,本研究公式解可为实际工程施工提供支护力参考值。曲线隧道极限支护力与土体内摩擦角、黏聚力及线路半径均呈负相关趋势,当隧道线路半径小于300 m时,隧道极限支护力波动幅度较大,而当线路半径大于600 m时,开挖面极限支护力逐渐接近直线隧道。在急曲线盾构隧道及不良地质情况下施工时需注意及时调整盾构参数来维持隧道开挖面稳定。

The curved shield tunnel of Tianjin Metro Line 11 is located at the water-rich sand layer,and it is difficult to control the excavation face stability due to the asymmetric thrust and seepage force of jack.Based on the silo theory and limit equilibrium method,the traditional wedge model was improved,and the inclined ladder-wedge prism model was established.The analytical formula of ultimate support force of shallow-buried curved shield tunnel excavation face affected by seepage was derived.The model results were verified by using numerical simulation and engineering examples,and the influence of parameters was analyzed.The result indicates that under the seepage,the seepage force constitutes an important part of ultimate support force of shallow-buried shield tunnel excavation face.Under the engineering geological conditions,the seepage force can account for 46%of ultimate support force at the highest,and the seepage force is greatly affected by the groundwater level.The theoretical calculation results of this model are close to the numerical simulation results with the error within 5%,which proves the rationality of three-dimensional calculation model proposed in this paper.To ensure the engineering safety in actual construction,the actual support force for shield tunnel is greater than the theoretical value of ultimate support force.The solution of this formula can provide the reference value for the actual engineering construction.The ultimate support force for curved tunnel is negatively correlated with the internal friction angle of soil,cohesion and line radius.When the tunnel line radius is less than 300 m,the ultimate support force for tunnel fluctuates greatly;when the tunnel line radius is over 600 m,the ultimate support force of excavation face gradually approaches the straight tunnel.During the construction on shield tunnel with sharp curve and under bad geological condition,it is necessary to adjust shield parameters in time to maintain the tunnel excavation stability.