Abstract:

In view of the construction condition that an overpass crosses over existing shield tunnels in Hefei, the construction parameter sensitivity analysis of singlepile adjacent to tunnel is carried out by finite element numerical simulation method, and the influence of singlebridge pile foundation and doublebridge pile foundation of overpass on the deformation and internal force of shield tunnel segment during construction and loadbearing stage is further studied. By comparing and analyzing the ground settlements, shield tunnel segments and track deformations under two crossingover modes of the overpass, the advantages and disadvantages of the two modes in engineering applications are discussed. The results show that: (1) The influence of singlepile on the adjacent tunnel structure increases with the increase of pile length and pile diameter; and decreases with the exponential function as the net spacing of piles and tunnels increases. (2) When the ratio between pile length and tunnel burial depth is greater than 1, increasing the pile length is an effective way to reduce the deformation of the tunnel structure. (3) The effect of the singlepier pile foundation construction on the shield tunnel is less than that of the loading stage, and the displacement of the segment is dominated by settlement; with an increase in the loading steps, the lateral axial force and transverse bending moment vary most in the tunnel arch which on the side of pile foundation; the longitudinal axial force and longitudinal bending moment vary most in the position of the tunnel vault. (4) When constructing double bridge pile foundation bearing upper load, the settlement at the same segment increases by 0.6 mm and the horizontal displacement decreases by 0.56 mm compared to the singlepier pile foundation. The method of crossing the tunnel without the intermediate pile is better.

Key words: pile foundation, existing tunnel, deformation, internal force, numerical simulation