考虑盾构铰接作用的小半径曲线隧道开挖诱发地层沉降分析

Analysis of ground settlement induced by small radius curve tunnel excavation considering shield articulation effect

目前针对小半径曲线隧道开挖诱发地层沉降的理论研究均将盾构机视为一个连续的整体,未考虑盾构机铰接装置带来的影响,由此不能正确评估小曲率盾构开挖路径变化带来的超挖效应等。首先,根据盾构机铰接位置以及盾构机与小曲率隧道开挖路径的几何位置关系,得到了小曲率隧道开挖过程中不同盾构铰接位置超挖量及盾构铰接角计算公式;其次,基于镜像法及Mindlin解,求解了铰接盾构施工时因超挖地层损失、盾尾地层损失、开挖面不均匀推力、盾壳不均匀摩擦力及盾尾处注浆压力等共同影响的地层沉降;最后,采用工程监测数据与理论解进行对比验证,得到较好的一致性。此外,针对隧道转弯半径、前盾长度、盾构铰接角及超挖量等进行了参数分析。分析结果表明:不考虑盾构铰接装置的影响将过高估计地层损失而导致地层沉降预测值偏大。随着转弯半径的减小,前盾长度、盾构铰接角及超挖量的增加,地层沉降增大,但其值变化均对开挖面前方沉降影响较小,对开挖面后方沉降影响较大。在开挖面后方,随着与开挖面距离的增大,当转弯半径取值较小,前盾长度、盾构铰接角及超挖量取值较大时,纵向地表沉降呈先增大后减小趋势。

Current theoretical studies of ground settlement induced by small radius curved tunnelling mostly consider the shield as a continuous whole and do not consider the effect of shield articulation.Therefore,the over-excavation gap caused by the change of excavation path of small curvature shield cannot be correctly evaluated.Firstly,based on the shield articulation position and the geometric position relationship between the shield and the small curvature tunnel excavation path,the calculation formulas were obtained for the over-excavation gap and articulated angle at different articulation positions of the shield machine during the excavation of the small curvature tunnel.Then,the mirror image method and Mindlin solution were used to solve the ground settlement caused by the combined effect of over-excavation ground loss,shield tail ground loss,excavation face uneven thrust,shield shell uneven friction and slurry pressure at the shield tail during articulated shield.Finally,engineering monitoring data were used to compare and verify with the theoretical solution of this paper,and good agreement was obtained.In addition,parametric analysis was carried out for the tunnel turning radius,front shield length,shield articulation angle and over-excavation gap.The analysis results show that ignoring the effect of shield articulation will overestimate the ground loss and result in large predictions of ground settlement.As the turning radius decreases,length of the front shield,shield articulation angle and over-excavation gap increases,the ground settlement increases,but the change of its value has a small effect on the settlement in front of the excavation face and a larger effect on the settlement behind the excavation face.Behind the excavation face,the longitudinal surface settlement tends to increase and then decrease as the distance from the excavation face increases,when the turning radius is taken to be small and the front shield length,shield articulation angle and over-excavation gap are taken to be large.