Study On The Response Of Internal Forces And Deformations Of Existing Pile Foundations To Tunneling

The existing buildings and buried pipelines will be affected inevitably by tunneling in urban areas. When the tunnel excavation under or adjacent to the pile foundations of buildings, stratum movements caused by tunneling will exert axial and lateral forces on adjacent piles, which may reduce the bearing capacity of piles and increase the differential settlement, thus superstructure is influenced. Obviously, it is important to study the responses of piles to nearby tunneling.In this paper, finite difference code is adopted and three-dimensional model is created. Though verifying an example proposed in Chen's paper, the model put forward by the author is available. Thereafter, the responses of single pile and pile groups to adjacent shield tunneling is investigated, some useful conclusions have been obtained, which can be used to guide practical engineering. The contents of this paper are outlined in details as the following:1. The responses of single pile to tunneling are analyzed with parameters, such as loads on the top of a pile, soil layers, longitudinal slop of a tunnel, double-tube-tunnel, elastic modulus of pile and pile diameter. It shows:①The axial force and vertical settlement along a pile increase with the increasing of the load on the top of a pile.②The internal force and deflection of a pile is apparently affected by the strength of soil in the region of three-hole-diameter-of-the-tunnel. Soil strength around the tunnel can be enhanced by some reinforce measures (such as grout and anchor), which can improve the force performance of the pile and ensure the safety of building structure.③The settlement of pile caused by the tunnel with gradient is smaller than that of pile caused the tunnel without gradient.④The excavation of double tunnel is adverse to the vertical bearing capacity and settlement of a pile, but it is advantageous to the lateral deflection and bending moment of the pile.⑤With the increasing of elastic modulus and diameters of the piles, axial force and bending moment of a pile will increase, then the capability to resist deflection of the pile is strengthened, and the differential settlement of the top and bottom of the pile is reduced.2. The responses of pile groups to tunneling are also studied with parameters, such as pile length, the horizontal distance between the tunnel and the pile, and the height of the cap of the pile. Research indicates:①When the load on the cap of the pile is definite, the axial force, horizontal movement and moments of the pile will increase as the increase of pile strength, and the settlement of the pile and vertical stress of soil under the cap of the pile will decrease.②The response of piles and soil between the piles to tunneling will decrease with the increasing of the horizontal distance between the tunnel and the pile.③The axial force and vertical settlement of the high cap pile is larger than that of the low cap pile, the horizontal movement and moments of the high cap pile is similar to that of the low cap pile.④Due to the "barrier effect" of the front pile, the responses of back pile to tunneling is smaller than the front pile, the axial force of back pile is larger than the axial force of front pile.Finally, some protection measures of pile foundations engineering are summed up and analyzed, then the partition wall is taken into consideration, an optimal scheme is gained through research on the size of the partition wall.