Structural Response And Safety Evaluation Of Large Diameter Slurry Shield Tunnel Under High Water Pressure

Nowadays,with the vigorous development of China's rail transit construction and the continuous improvement of shield tunnel technology,a large number of tunnels have begun to be built through water.It is increasingly a traffic lifeline between regions and even countries because it is not affected by climatic conditions,resists war damage and does not affect shipping.Even the lifeline of traffic between countries.Due to the problems of high water pressure,long distance,large diameter and complicated geological conditions,the single-layer lining can not meet the engineering requirements,and the composite lining structure is gradually adopted.This also makes the load state of the tunnel composite lining structure more difficult to distinguish.It is very important to evaluate the mechanical response characteristics and the denaturing law of underwater shield tunnel composite lining structure.This article relies on the shield tunnel through rivers of Wuhan Metro Line 8.The project is currently the largest single-tube two-line subway shield tunnel in China,and a composited shell-connector model is established.The main research contents and results of this paper are as fo lows:1.Aiming at the engineering difficulties such as high water pressure,crossing the Yangtze River and upper soft and hard stratum,a load value method which is more complex with actual working conditions is proposed.According to the nature of the stratum soil,combined with the influence width caused by the excavation of the uneven formation,the calculation formula of the soil pressure under the condition of composite stratum is optimized.Based on the seepage theory,the calculation formula of water pressure under high water pressure conditions is improved,and the accuracy of calculating water and soil pressure is improved.According to the obtained water and soil pressure,a simplified calculation model of shield top thrust is established.The nonlinear dynamic calculation formula of the large-diameter mud-water shield top thrust is derived.Comparing the measured data,the correctness of the calculation formula is verified,and the reliability of the load value method is determined.2.The calculation method of the existing lining structure of shield tunnel is analyzed in detail,and an improved shell-connector model is established.The model uses the connector unit to simulate the interlayer interaction mechanism and the segment joint.The connector unit can set nonlinear stiffness and displacement failure criteria in different directions,which greatly improves the accuracy of the simulation.The formation parameters and lining parameters of typical sections are assigned to the model,and numerical simulation and calculation analysis are carried out.The changes of the mechanical characteristics and displacement response of the lining of the lining before and after the secondary lining were compared and analyzed,and the influence of the secondary lining on the lining of the segment was determined.The simulation results are compared with the on-site monitoring data to verify the reliability and accuracy of the model.3.On the basis of the established numerical model,the participating bearing ratio,secondary lining thickness and secondary lining concrete strength grade of the lining structure are taken as a single variable.The necessity of joint bearing of secondary lining is clarnfied.The safety reserve function of the secondary lining was verified.The mechanism and influence law of lining participation ratio,secondary lining thickness and secondary lining concrete strength grade on the mechanical characteristics and displacement response of lining structure are summarized.The safety evaluation of the design parameters of the secondary lining of the project is proposed.