| This paper was based on the Chongqing Huo fengshan 2 line tunnel as the background,Using ANSYS software to make reasonable assumptions and established numerical models.The deformation and internal force changes of the pile foundation in the deep and shallow buried tunnels are studied under the dip angle of different strata ?i(i=1~5 and ?1=0°,?2=10°,?3=20°,?4=30°,?5=40°).The extreme value of the dip angle under different buried depth is obtained through the fitting data.Secondly,under the circumstances of adopting the CRD method in the three lane tunnel with small net distance,four factors such as the surrounding rock grade,the bearing load,the pile length and the pile diameter ware considered.Through establishing of the orthogonal test of the four factors and three levels,the influence of four factors on the pile foundation was obtained by the extreme value R.Then,combined with the actual project to establish a corresponding finite element model,analyzed the variation of displacement,deformation and internal force of the pile foundation and the superstructure of the tunnel before and after the opening of the tunnel.Finally,the main control measures for the influence of tunnel construction on pile foundation stability ware introduced,and confirmed that the reinforcement of pile surrounding soil can increase the capacity of pile to resist deformation.The main conclusions drawn as follows:(1)In grade ? surrounding rock,when the buried depth of the three lane deep burial tunnel with small distance is 32.1m,in the case of formation dip angle ?= 0 °,the surface horizontal deformation law is approximate to the anti-symmetric distribution.With the increasing of dip angle of the stratum,uniform settlement is observed for each pile foundation,and the maximum settlement difference is not more than 2mm.The horizontal and settlement displacement of pile Z3 and Z4 at the end of the pile is fitted to the first order exponential relationship with the dip angle of the stratum,and according to the code,the maximum allowable value of the dip angle of the formation is about 55 degrees.(2)In grade ? surrounding rock,when the buried depth of the three shallow burial lane tunnel with small distance is 18.5m,in the case of formation dip angle ?= 0 °,thesurface subsidence deformation is approximately "W",the width of the settlement trough is 2 × 25 m,which is similar to the calculated result of the Peck formula,and the surface horizontal deformation law is also an anti-symmetric distribution.With the increasing of ?,the range of soil moving to the left increases gradually.The maximum settlement value on the left side of the middle rock axis is located in the left tunnel 1B(B is the span of the tunnel).The settlement of each pile is uniform and the settlement has a tendency to increase,and the difference settlement is not more than 5mm.Finally,the horizontal and settlement displacement of pile Z2 and Z3 at the end of the pile is fitted to the first order exponential relationship with the formation dip angle.The maximum allowable dip angle is about 43 degrees..(3)Through the extreme value R,the order of influence of four factors on the horizontal displacement of pile foundation is as follows: surrounding rock grade > pile diameter > pile length > bearing platform load.The order of vertical displacement of piles is: Surrounding rock grade > bearing platform load > pile diameter > pile length.The order of pile axial force is: Surrounding rock grade > pile diameter > bearing platform load > pile length.The influence factors have two parabolic relations on the maximum bending moment of pile body,and the linear relationship between the grade of the surrounding rock and the maximum shear force of the pile body.(4)Combined with the actual project,the numerical calculation models ware set up,it was obtained that the small distance tunnel by CRD method had a small impact on the vertical and horizontal displacement of the upper structure.The horizontal displacement of the upper structure increases gradually along the height of the building,similar to the physical "whiplash effect" phenomenon.After the tunnel excavation,The horizontal displacement of the pile foundation near the tunnel is left,and the horizontal displacement of the pile foundation on the far side of the tunnel is right,The maximum displacement values are located in the middle side of the pile body.The variation laws of field measured data and numerical simulation results are roughly the same,and it also confirmed the feasibility of the numerical simulation and the necessity of the monitor. |
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