Research On Influence And Control Of Shield Tunnel Passing Through Existing Tunnel

The upper and lower construction of shield tunnels is a difficult type of the adjacent construction.The safety control of the shield tunnel under the existing tunnel is an important research topic.The analytical formula method and FLAC3 D numerical simulation were used to study the mechanical response of the existing tunnel caused by the underpass construction of the shield,and the importance ranking and multi-objective optimization of the construction parameter monitoring data of the shield machine passing through the intersection of the existing tunnel is conducted.The main work and research results of this article are as follows:(1)This paper proposes an analytical solution method based on two-stage analysis method.In the first stage,the additional stress at the location of the existing tunnel axis caused by many factors is obtained.In the second stage,the existing tunnel is regarded as Euler-Bernoulli beam on the Parsternak double-parameter foundation,and the deformation stiffness equation of the beam is established to analyzes the law of the influence of the elastic modulus,clearance and ground loss rate on the existing tunnel.(2)The finite difference software FLAC3 D was used to establish a three-dimensional model of the shield tunnel under the existing tunnel,and the shield construction parameters were simulated carefully.The influence of shield excavation on the existing tunnel is mainly studied from the aspects of stratum displacement,settlement of existing structure,stress increment and additional internal force.From the different influencing factors,the change law of stress increment and deformation of the existing tunnel caused by the underpass construction of the shield is analyzed.According to the proximity formula,formulate the proximity of the tunnel spacing ratio and buried depth ratio,and a set of corresponding safety control countermeasures for under-shield construction is put forward.(3)Taking the shield parameter monitoring data of the actual engineering shield crossing the intersection as the training sample,the random forest feature importanceranking shows that the propulsion force and the earth cabin pressure have the most significant impact on the displacement of the arch of the existing tunnel.Based on the GA-LSSVM regression prediction model,NSGA-Ⅱ is used to obtain the combination of shield construction parameters under the optimal conditions of horizontal displacement and settlement of the arch bottom of the existing tunnel,which provides guidance for the optimization of actual shield construction parameters.