Influence Analysis And Prediction Of Shield Tunneling Parameters In Composite Strata

Composite stratum is the most common stratum type in shield tunnel construction,but the research on shield tunneling parameters in composite stratum is relatively less.As a modern advanced construction method with high mechanization,automation and data,shield construction method is developing along the direction of big data and artificial intelligence.However,the selection of shield tunneling parameters depends on field experience.In order to solve such problems,this paper relied on the Hubai tunnel project of Changsha Rail Transit Line 6,established the prediction model of shield tunneling parameters based on RF random forest algorithm,and verified its reliability.Theoretical research and numerical simulation were used to analyze the influence of shield tunneling parameters on segment structure and surface settlement.The main research contents are as follows:(1)The data histogram and variation curve were plotted by mathematical statistics,and the variation lawed of five main shield tunneling parameters of shield tunnel under different stratum conditions were studied.Spearman correlation analysis revealed the correlation between the main tunneling parameters.The research results showed that the soil properties of the excavation face are changed due to the continuous change of stratum properties in the tunneling construction of shield under the condition of composite stratum,which makes the shield parameters fluctuate.(2)Based on the modified spring-beam load system,the load-structure model was established by using the finite element analysis software,and the mechanical properties of segment considering the thrust of jack under the condition of composite stratum were analyzed.The analysis results showed that when the shield crosses the upper soft and lower hard strata,the deformation of segment vault is much larger than that of arch bottom.The influence of jack thrust on the deformation of segment ring is all-round.When the jack thrust increases,the segment ring expands outward as a whole,thus affecting the stability of the segment.(3)Based on the linear regression analysis of the measured settlement data,the modified Peck formula suitable for the settlement prediction of the surrounding area of the project was calculated.The stratum-structure model was established by finite element analysis software,and the effects of jack total thrust,soil chamber pressure and grouting pressure on ground settlement and stratum loss rate of shield tunnel were analyzed.The research showed that when predicting the ground settlement at the construction site of composite stratum shield in Changsha,the modified Peck formula can make the prediction results more accurate.The above shield parameters are sorted from large to small according to the influence degree of stratum loss rate and surface settlement,which are total thrust of jack,grouting pressure and earth cabin pressure.(4)The PSO-RF hybrid algorithm model based on RF random forest algorithm was established by using MATLAB programming software to predict the shield tunneling parameters and verify the error of the prediction results.The research showed that after the PSO-RF hybrid algorithm model established in this paper is trained and studied,the average error between the predicted and actual values of the five shield parameters is within 15%,that is,the prediction results can meet the verification requirements of generalization ability and prediction ability.