Study on the influence of pipe jacking construction on existing subway tunnels

To study the influence of pipe-jacking construction on adjacent existing pipelines, take a project where a pipe-jacking tunnel closely crossed over the existing Metro Line 5 in Xi’an as the background. The laws of surface settlement, earth pressure, and the force and deformation of the existing tunnel caused by the construction of the new tunnel crossing over were obtained by combining centrifugal model tests and numerical simulations. The results show that: (1) The surface settlement caused by tunnel excavation in sandy stratum was divided into three stages: severe deformation, slow deformation, and stable deformation. For any position on the surface, the disturbance caused by the approaching of the excavation face was greater than that caused by the leaving. (2) The upward crossing construction increased the earth pressure on the near side of the existing tunnel near the new tunnel axis and reduced the earth pressure on the far side. The range of the earth pressure reduction area was positively correlated with the net distance between the tunnels. (3) After the upward crossing construction, the change of the additional bending moment in the longitudinal direction of the existing tunnel was much greater than that in the circumferential direction. The maximum additional bending moment in the longitudinal took place at the intersection of the tunnels. After passing the inflection point, the negative bending moment increased sharply. The curve of bending moment conformed to the Gaussian distribution. The larger the net distance between the tunnels and the smaller the overall burial depth, the smaller the maximum additional bending moment in the longitudinal. The change of the net distance changed the position of the inflection point. (4) The construction of pipe-jacking caused the existing tunnel to rise and deform, with the shape of an inverted “V”. The smaller the overall burial depth of the tunnel, the smaller the range of the existing tunnel rise, and the shape of the inverted “V” is lower and wider.