小转弯半径曲线盾构隧道开挖引发地表沉降计算

小转弯半径曲线盾构隧道施工引发的地表沉降变形规律极为复杂,但相应的变形预测解析公式仍未明确。依据前人研究成果,构建曲线段盾构隧道施工的地层损失模型,基于镜像法及Mindlin解,推导曲线盾构隧道开挖引发地表沉降的计算公式,并将其应用于工程实例计算,最后分析曲线盾构隧道施工引发地表变形规律及其影响因素。研究表明:构建的小转弯半径曲线段地层损失模型合理,推导所得公式适用于实际工程计算;地表纵向沉降在靠近刀盘3倍洞径范围内变化极大,刀盘前方3倍洞径范围内地表会产生轻微隆起,刀盘后方3~4倍洞径处出现最大沉降;地表横向沉降槽为非对称分布,最大沉降位置位于弯道内侧,距刀盘中心线约1倍洞径;地层损失引起的地表横向沉降大小主要受转弯半径及盾壳长度影响,地表横向沉降槽偏移程度主要由刀盘直径大小决定。

Calculation of surface settlement caused by excavation of shield tunnels with small turning radius

The settlement deformation caused by the construction of shield tunnels with small turning radius curve is very complicated,but the corresponding analytical method of deformation prediction is still not clear.According to the results of the previous researches,the formation loss model for construction of shield tunnels with curved section is established.Based on the mirror image method and the Mindlin solution,the formula for calculating the surface settlement caused by the excavation of shield tunnels with curved section is derived and applied to the calculation of engineering examples.Finally,the surface deformation laws and influencing factors of construction of shield tunnels with curved section are analyzed.The results show that the model for formation loss of curved section is reasonable and the derived formula is applicable to practical projects.The longitudinal surface settlement varies greatly in the range of 3 times the diameter of the hole close to the cutter head,a slight bulge on the surface within 3 times the hole diameter in front of the cutter head,and the maximum settlement position is located at 3~4 times the hole diameter behind the cutter head.The surface transverse settlement groove is asymmetrically distributed,and the maximum settlement position is at the inner side of the bend,about 1 time the hole diameter from the center line of the cutter disc.The surface settlement caused by formation loss is mainly affected by the turning radius and the length of the shield and shell,and the displacement degree of the surface transverse settlement groove is mainly affected by the diameter of the cutter disc.