软土地层下穿开挖引发上覆电缆隧道挠曲变形分析

Deflection Analysis of Cable Tunnels Due to Underpass Excavation in Soft Soils

软土地区电缆隧道埋深浅、结构刚度低,易受下穿隧道近接施工的扰动影响,严重时可能导致变形超限、破损或开裂等结构病害.然而,评估软土隧道开挖对上覆电缆隧道扰动影响的理论方法仍相对欠缺.基于此,提出一种隧道扰动下电缆隧道挠曲响应的有限差分理论分析方法,其中,假设电缆隧道符合Timoshenko梁,隧道周边地层简化为Winkler地基,采用有限差分法求解电缆隧道的变形和受力.计算结果与梁-弹簧法数值模拟结果吻合较好,验证了该方法的有效性.进一步对影响电缆隧道挠曲变形的主要因素进行了对比分析,结果表明:电缆隧道竖向位移随着隧道横截面宽度b和高度h的增加而减小,而弯矩随截面宽度b和高度h的增大而增大.相对而言,高度h对竖向位移和弯矩的影响更大.相较于高度为2.6m的电缆隧道,高度为4.4m的电缆隧道最大位移减小约30%,弯矩则增大约50%.当地层损失率V1为6%时,最大弯矩将超过混凝土极限抗拉弯矩,此时电缆隧道处于不安全状态.

Cable tunnels in soft soils have relatively shallow burial depth and low structural stiffness,being susceptible to disturbance of underpass excavations.Severe deformation and structural failures might be caused under such conditions.However,theoretical method to evaluate the impact of excavation disturbance on the overlying cable tunnels is still in a lack.This study proposes a finite difference-based solution for the response of cable tunnels under underpass excavations.The cable tunnel is simplified as a Timoshenko beam,and the surrounding soils are treated as Winkler foundation.The deflection deformation and stress of the cable tunnel can be solved.The results are in good agreement with the beam-on-spring finite element simulations,which shows the effectiveness of the proposed method.Then,a parametric analysis is conducted on the main affecting factors.The results show that the vertical displacement of cable tunnel decreases with the increase of section width and height(h),while the bending moment increases with the increase of section width and height.Compared with the cable tunnel with a height of 2.6m,the maximum displacement of the cable tunnel with a height of 4.4m is reduced by about 30%,and the bending moment is increased by about 50%.When the volume loss ratio is 6%,the maximum bending moment will exceed the ultimate tensile bending moment of concrete,leading to the unsafe state of the cable tunnel.