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

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.