Research On Influence Of Tunneling On Adjacent Group Pile Of Nanning In Guangxi

Subway tunnels are usually built in the area with intensive buildings, in which pile foundations are widely used. Consequently the subway tunnel construction is inevitably close to or through the existing building and lead to ground loss, stress changing, ground deformation, the additional bending axial force and bending moment of piles. Accordingly, the piles are deformed and the settlement force is generated so that the carrying capacity of the surrounding existing buildings are reduced. Based on the current existing research, centrifugal model tests were carried out to study the influence of single and double tunneling on nearby piles. Then numerical analysis was applied on the centrifuge model tests, and the mutual authentication was applied between thetwomethods. Based on the confirmed numerical model, the law of influence of single and double tunnel construction on adjacent ground piles vertical subsidence of surface, additional deformation, additional bending moment and additional axial force with different depth were analyzed.Conclusions can be drawn as follows:(1) The law of surface vertical subsidence induced by tunneling with different depth was similar, and the maximum subsidence can be acquired above the tunnel center. (2) During the process of tunnel excavation, the settlement caused by tunneling at pile top increase with tunnel excavation; the cushion cap was tilted because of the step-by-step excavation; the redistribution of internal force of pile foundation was then generated. (3) When the depth of tunnel is greater than or equal to the depth of group piles, the force mode of adjacent pile which force performance caused by tunneling is cantilever beam mode, or else the force mode of pile force performance is beam hinged at two ends. The deeper the depth of tunnel is, the smaller the influence caused by tunnel excavation of group pile is. (4) After the process of twin tunnel excavation, regardless of the tunnel’s depth, the additional axial force of front pile showed positive, and the pile axial force increased. When the depth of tunnel axis is less than or equal to the depth of pile, the additional axial force of real pile was positive, and the pile axial force increased, or else the additional axial force of real pile was negative, and the pile axial force decreased.The research results are hopefully to provide essential theoretical supports for the design and construction of tunnels which are adjacent to buildings in Guangxi area.