Analysis Of The Tunneling Excavation Effect On The Pile Group Of Adjacent Buildings

In order to solve the congestion of ground transportation, many cities in China areconstructing the subway tunnel or planning to undertake such a project. In the processof constructing the urban subway tunnel, tunnel excavation inevitably causes the soilmovement and displacement of the pile group base around the tunnel, which haveadverse effects on buildings. In this study, the finite difference analysis softwareFLAC3D is used to investigate the influences of tunnel excavation on the soilmovements and the features of pile behavior. In the numerical model calculations,linear elastic material is used for the concrete lining, the Mohr-Coulomb elastic-plasticmodel is used for soil, and Pile is used for pile foundation.In the first place, this paper analyzes the movement of soil around the tunnel causedby the tunnel excavation. The empirical method, analytic method and numericalanalysis software are employed to calculate the surface subsidence, horizontaldisplacement, the side of tunnel soil horizontal displacement and vertical displacementafter the tunnel excavation. The following conclusions are drawn by analyzing theresults:（1）The tunnel excavation exerts a comparatively great impact on the soilaround the excavation, and the distance is approximately2D(D is the tunneldiameter).（2）After the tunnel excavation, lining becomes oval under the soil pressure.Lining deformation squeezes the soil, so the soil tends to deviate from the direction ofthe tunnel section. Thus the soil horizontal displacement relatively decreases.（3）Thesoil surface subsidence and horizontal displacement will decrease, if the stiffness ofconcrete lining increases.Next, the finite difference software FLAC3D was used to study the tunneling effectson neighboring pile group foundation and analyze the shielding effect of a pile groupadjacent to tunneling by considering the piles, soil and tunnels as a whole. The resultsfrom the two-stage method were compared with that of the FLAC3D to verify thereasonableness of the numerical simulation results. The results are:（1）Shielding effectof pile group increases while the pile spacing decreases, and when the pile spacingincreases to a certain extent, shielding effect can be ignored.（2）Shielding effect on theback piles is greater than that on the front row piles during the tunnel excavation.Finally, the inner force, displacements and other aspects of piles are investigatedduring tunnel construction phases in order to examine the change of pile foundation.Meanwhile, the impact of pile with different lengths of piles and distances from the tunnel axis caused by tunnel excavation is also explored. Numerical simulationanalysis shows that:（1）Pile internal force increases with the increase of pile lengthduring the tunnel excavation. Especially when the pile end is below the horizontal axisof the tunnel, pile internal force increases significantly.（2）Maximum bending momentand maximum axial force decrease with the increase of the distance between piles andtunnel axis.The conclusions obtained from this study merit attention in assessing the tunnelexcavation on adjacent pile foundation in engineering project.