Study On Mechanical Behavior And Construction Technology Of Underwater Shield Tunneling In Sandy Soil Layer

In recent years,China's underwater shield tunnel project has entered a new stage of rapid development.Because of its unfavorable conditions such as shallow thickness and high water pressure,it often faces the risk of collapse of the excavation surface and leakage of water.,making the stability of the tunnel excavation surface extremely difficult to control.Therefore,it is of great practical significance to study the stability of the excavation face of shield tunnel under high water pressure conditions.This paper combines the case study of the lower reaches of the Dong Zhuang Station to the Convention and Exhibition Center Station of the second phase of the Shijiazhuang Metro Line 1 project.The theoretical analysis,numerical analysis and on-site measurement are used as research methods to study the sand under high water pressure conditions.Stability problem of excavation face of mud-water shield tunnel in soil layer.The main work and research results include the following aspects:?1?Based on the critical depth burial formula of the tunnel proposed in[34],the Rankine passive earth pressure obtained from the plane strain formula derived from the Lade-Duncan criterion is introduced as the normal stress limit in the arch span.When calculating the water-soil pressure Considering the influence of water permeability,the formula for determining the critical depth of soil tunnels in accordance with the underwater tunnel subject conditions is finally obtained.?2?From the obtained analytical formula of critical depth,the parameters?internal friction angle?,water depth hwh and permeability factor??which have direct influence on the arching conditions are extracted.By designing orthogonal experiments,the following conclusions are drawn:critical buried depth value H_cr and the friction angle?is inversely proportional to the water depth hw,and increases with the increase of the permeability factor??3?With the help of the finite difference software FLAC^3D software,the fluid-solid coupling analysis model is established,and the process of the shield tunneling through the Weihe River is simulated.It is found that the tunnel cannot form a stable pressure arch.Comparing the settlement of the vault of the target section with the convergence of the horizontal clearance and the measured results,the errors are finally 0.227mm and 0.319mm respectively,and the error is small.The numerical simulation results are verified.?4?On the basis of the original model,the design buried depth is increased.It is found that the buried depth reaches 28m?where the friction angle?of the soil is 30°,the water depth hw is 5m,and the permeability factor?is 0.75?,and the maximum principal stress direction directly above the dome is generated.The change has reached the condition that a stable pressure arch can be formed,and the analytical result of the analytical formula is 27.4 m,which are relatively close.?5?The influence parameters in the analytical formula are extracted,and orthogonal experiments are designed respectively.It is concluded that the maximum deformation value of the tunnel is inversely proportional to the friction angle?,which is proportional to the river depth h_w and the permeability factor?.