A Back-analysis Approach Based On The Finite Element Method And Artificial Neuron Network And Application In Tunnel Engineering

The structural stress characteristics and stratum response law during the tunnel construction process are the key issues to break through the bottleneck of tunnel safety construction evolution and formation mechanism.The numerical method can provide a feasible method for analyzing this problem.Due to the complexity and uncertainties of the surrounding stratum,it is generally difficult to determine the parameters used in the material constitutive model.In this paper,the back analysis method composed of artificial neural network and finite element method was introduced to the tunnel engineering.Based on the temporal monitoring data of the ground settlement during the tunnel construction,an inverse analysis process was presented to determine the constitutive parameters.By using the determined parameters,an in-house code accounting for threedimensional nonlinear contact problems was used to analyze the multi-body contact system arising from the tunnel engineering.Based on the numerical results,the interfacial contact behavior between the concrete and the stratum was discussed.The influence of the contact behavior on the concrete was also studied.The main results obtained in this paper are as follows:(1)A case study of the "Tumor Hospital Station-Tianjin Hotel Station" section of Tianjin Metro Line 6 was investigated.Based on the statistical analysis of the monitoring data,the vertical and horizontal distribution characteristics of the ground settlement induced by the tunnel construction were discussed.The monitoring data used for back analysis was then determined.The tendency of the ground settlement and stratum loss caused by the tunnel excavation in silty clay soil in Tianjin area was studied.This provides a solid reference for the design,construction and safety assessment of subsequent projects.(2)A sensitive analysis of the main factors influencing the stratum deformation of the shield tunnel was conducted by using the finite element method.Based on the results of the sensitive analysis,the factors having significant influence on the ground deformation were obtained.The specific values of these factors will be further determined by the back analysis.The underdetermined factors are the Young's modulus,the Poisson's ratio,cohesion,internal friction angle and the grouting-associated modulus.(3)The back analysis scheme used in this paper is composed of the finite element method as well as a artificial neural network,which is optimized by using Vogl's algorithm and evolutionary calculation.This scheme is used to determine the constitutive model parameters of soil based on the temporal monitoring data of surface settlement during tunnel construction.By using these determined parameters,the numerical results achieve a good agreement with the monitoring data.This agreement indicates that the back analysis scheme is applicable for tunnel engineering and provides a solid basis for further nonlinear contact analysis.(4)The dual mortar finite element method was used to validate its applicability for treating nonconforming meshes in tunnel engineering.The permitting of using nonconforming meshes introduces a significant flexibility to the numerical simulation.Then,the dual mortar finite element method was used to numerically analyze the multibody contact system arising from the tunnel engineering.The stress and deformation characteristics of the concrete segments were investigated,with the focus on the nonlinear contact behavior of the soil-structure interface.