Study On The Mechanical Response Of Above-crossing Or Under-crossing Tunnelling On The Existing Tunnel

With the accelerating of urbanization process,there will be more and more cases of new subways crossing existing shield tunnel.It is the most basic goal to ensure the normal operation of existing lines during the design process.It is very important for the safe operation of existing subway tunnel by analyzing the mechanical behavior of existing.This thesis integrated the theoretical analysis,the three-dimensional numerical simulation,the transparent soil and the neural network to study the effect of new shield tunnel above-crossing or under-crossing on the existing shield tunnel.The main contents and research findings of this thesis were as follows:(1)A two-stage analysis method was used to study the effect of new shield tunnel above-crossing or under-crossing on existing shield tunnel.It was found that the existing shield tunnel was uplift when the new shield tunnel above-crossing and the existing shield tunnel was settlement when the new shield tunnel was under-crossing.The maximum value of uplift or settlement was at the intersection of two tunnels.The deformation curves were approximately consistent with the Gauss normal distribution.The location of the maximum bending moment of the existing shield tunnel was the same as the location of the maximum deformation.The maximum shear force was located on both sides of the existing shield tunnel axis.During above-crossing tunneling,the influence of the existing shield tunnel became smaller with the increasing of distance between the existing shield tunnel and the new shield tunnel.The change of Poisson's ratio had no effect on the existing shield tunnel.During under-crossing tunneling,the stratum loss rate and the distance between the existing shield tunnel and the new shield tunnel had a greater impact on the existing shield tunnel,while the Poisson's ratio had no effect.(2)By building a three-dimensional finite element model to analyze the effect of above-crossing or under-crossing tunneling on the existing shield tunnel.It was found that the impact of the new shield tunnel excavation in horizontal direction was mainly located at 1.5D.The impact of existing shield tunnel had been significantly weakened with grouting pressure and distance.(3)According to the results of numerical simulation and theoretical analysis,the existing shield tunnel was more affected in under-crossing tunneling.The combination of transparent soil and PIV were used to simulate the process of new shield tunnel passing through existing shield tunnel.It was found the existing shield tunnel sank.The deformation of the existing shield tunnel was gradually increased with the new shield tunnel tunneling.(4)The BP neural network model was used to predict the impact of the existing shield tunnel with the new shield tunneling in a certain range of grouting pressure,while the prediction had a certain randomness.It was necessary to meet the requirements through multiple training.The prediction accuracy of the deformation was lower than the prediction results of bending moment and shear force.