Research On Inversion Of Strata Parameters And Subsidence Control Of Shield Tunnel Under-passing Expressway

The shield method has the advantages of strong stratum adaptability,safe and controllable construction process,and little impact on the surface and surrounding environment.It plays an increasingly important role in the construction of urban rail transit.When the shield tunnels under-passing the expressway in operation,in order to ensure the safety and stability of the expressway operation during the under-passing process,it is necessary to formulate strict subgrade settlement control standards.In addition,when rail transit runs under the expressway,it often faces the problem of missing geological parameters in the under-passing section due to limited survey,which further increases the difficulty of controlling the subgrade settlement.Therefore,this paper relies on the "Jinyidong" rail transit shield to pass through the Changshen Expressway project,and carries out relevant research on the problem of missing parameters and subgrade settlement control problems encountered in the process of under-passing.The main research work and related achievements are as follows:(1)Combined with the problem of missing parameters in the underpassing section of the project,an inverse analysis method is proposed on the basis of summarizing the common processing methods for missing parameters.The shield tunneling parameters and surface subsidence monitoring data of the test section before the under-pass are analyzed.The results show that the project has the conditions for back analysis,and the data samples used for the back analysis are determined based on the actual situation of the test section before the under-passing.(2)The training data set was constructed by combining the LOLAVoronoi adaptive sampling algorithm and finite element numerical simulation,and then the model was trained by the BP neural network,and the highly sensitive parameters missing in the under-passing section of the shield were obtained by inversion.The result shows that the data set obtained by the adaptive sampling method is better than the data set obtained by one-time sampling,and the inversion effect can be improved by increasing the number of monitoring sections and the number of monitoring points on the same section.The inversion parameters are used to predict the surface subsidence based on the engineering,and the comparison and analysis with the measured results verify the reliability of the data set construction method.(3)Based on the parameters obtained by the inversion analysis,the numerical simulation of the whole process of the shield tunnel under-passing the expressway was carried out,and the variation law of the subgrade settlement during the construction of the shield tunnel under-passing was studied.The comparison with the measured results is in good agreement,which provides guidance for the safety control of under-pass construction.(4)The grey relational analysis is used to screen out the construction parameters that have a great influence on the surface settlement,and the control measures taken to control the subgrade settlement are analyzed in combination with the change curve of each parameter.Summarize the settlement control technology of shield tunnel under highway subgrade from two aspects of construction parameters and construction process.Finally,the control effect of the subgrade settlement in the actual under-passing process is evaluated based on the monitoring data of subgrade settlement and the operation of the expressway.