Research On Prediction Of Vertical Position And Attitude In Shield Tunneling Based On "MGRU-Sobol"

With the rapid development of urban rail transit construction in China,the shield has been widely used because of its construction advantages.During the shield construction,untimely or improper control of position and attitude of tunnel will cause problems such as segment misalignment and rupture,ground subsidence,et al.In serious cases,the tunnel route may even need to be redesigned,so timely and effective control is the guarantee for one of the key links of construction safety and quality.Existing research is mainly focused on the correction of shield position and attitude,but there are few prediction studies related to the advance control of shield posture,and few studies take into account the“lag effect”of shield posture.Faced with the complex problem of multi-factor coupling effect of shield position and attitude,this paper is based on the prior control of shield position and attitude,based on the analysis of shield tunneling posture mechanical model and considering its“lag effect”,the establishment of the Gated Recurrent Unit-Sobol Global Sensitivity Analysis(“MGRU-Sobol”)prediction system for the vertical position and attitude of shield tunneling,and its practical applicability is tested through engineering cases,which provides theoretical support and practical guidance for the advance control of shield position and attitude in actual construction.The main research contents include:(1)Taking the vertical position and attitude of shield tunneling as the research object,the shield tunneling position and posture mechanics model was established to extract the factors affecting the shield position and attitude,and the shield tunneling parameters,geological parameters and geometric parameters were established as models input and vertical trend and pitch angle as model output for shield tunneling vertical position and posture prediction index system.Considering the perturbation and uncertainty of the construction data itself,a series of data preprocessing strategies including data outliers,missing values,and normalization processing have been established to provide data support for the establishment and training of the prediction models.(2)In order to solve the problem of vertical position and attitude prediction of shield tunneling,based on the actual construction data as the driving force,on the basis of determining the input and output of the prediction model,the“MGRU-Sobol”prediction system was established.That is from the framework of the prediction model,the division of training data,the optimization of hyperparameters,the determination of the objective function and optimization algorithm,and the overfitting of the model have achieved the establishment of the MGRU prediction model for the vertical position and attitude of the shield tunneling;the parameters of each model are determined based on the K-S test method based on the data distribution characteristics,a large number of samples are obtained by Latin sampling method,and the Sobol’global sensitivity analysis of the MGRU prediction model parameters is performed by Monte Carlo simulation to obtain the first order,the total order and the coupling sensitivity index.(3)In order to verify the practical applicability of the established“MGRU-Sobol”shield tunneling vertical position and attitude prediction system,an example application was carried out by relying on the shield interval of a pebble underlying mudstone stratum on the No.2 line of Chengdu Metro Line 8.The accuracy of the MGRU shield tunneling vertical position and attitude prediction models are RMSE=0.083,R~2=0.998;RMSE=0.077,R~2=0.996,which are higher than the predictions of the long and short-term time memory network(LSTM)model and the BP neural network model The accuracy proves the applicability and reliability of the MGRU model in the prediction of the vertical position and attitude of the shield tunneling;the first order,the total order and the coupling sensitivity index of the MGRU prediction model parameters are obtained by the Sobol’method,and the sensitivity is discussed robustness and convergence of calculation results.The application results show that the prediction system established in this paper can effectively solve the problem of vertical position and attitude prediction of shield tunneling,and can provide theoretical guidance for the advance control of shield posture in actual construction.