Study On The Influence Of Shield Tunnel Face Instability On Surrounding Rock And Existing Pile Foundation

As a new transportation means to relieve the pressure of traditional urban transportation system,metro construction is on the agenda of more and more cities.Shield method,as a safe and reliable tunneling method,is widely used in the construction of urban metro.However,the shield construction operation in the complex geological conditions below the urban surface obviously has certain safety risks.Therefore,it is undoubtedly of practical significance to control the palm face support force to reduce the disturbance of tunnel construction to the tunnel surrounding rock and adjacent buildings（structures）.In this thesis,we firstly investigate the transparency and physical and mechanical properties of self-prepared transparent soil,and secondly design a model test device and conduct model tests to study the deformation pattern of soil and pile deformation trend caused by palm face instability under different conditions.Finally,numerical simulations are used to reproduce the model tests and the results are compared and verified to prove the reliability of the conclusions.The main work and conclusions are as follows.（1）Based on the summary of the current commonly used transparent soil preparation methods,a transparent sandy soil was prepared by selecting fused silica sand and a mixture of n-dodecane and No.15 white oil,testing the optimal ratio of n-dodecane to No.15 white oil at 20°C,and conducting a series of physical and mechanical property tests on the transparent soil to verify its feasibility as a natural soil substitute in the model tests.（2）A shield tunnel testing device based on transparent soil technology was designed and fabricated to visualize the internal deformation of the soil and the displacement trend of the pile foundation.（3）Model tests were carried out for the deformation of soil and pile foundation caused by the destabilization of shield tunnel palm surface under different conditions.The results show that the deformation of the sandy soil stratum caused by the destabilization of the shield tunnel palm face is a bottom-up progressive process,with the reduction of the palm face pressure,the soil in front of the palm face is the first to be loosened,and close to the vertical upward development to the upper soil,and finally penetrate to the surface,the overall destabilization of the stratum occurs.The deformation of pile foundation in the destabilization process of shield tunnel palm surface increases with the decrease of palm surface support force,and the displacement of pile body to palm surface occurs as a whole,the smaller the pile-tunnel spacing the greater the pile foundation is disturbed.（4）Based on the numerical simulation software to reproduce the model test,the results show that the deformation of the surrounding rock develops from bottom to top,the surface settlement of the stratum with the burial depth ratio of 1 is larger than that of the stratum with the burial depth ratio of 2,but the affected range of the surface is smaller than that of the stratum with the burial depth ratio of 2;the pile foundation is displaced toward the palm surface as the support force of the palm surface decreases,and the smaller the pile-tunnel spacing is,the greater the pile foundation is disturbed.The law is similar to the model test results,which indicates that the overall results have some reasonableness.