Research On Pressure Setting Of Soil Bunker Crossing The River Under Double-line Shield Tunneling And Its Impact On Surface Displacement

With the rapid development of urbanization,the population size and building density are increasing,and the construction environment of urban underground rail transit is becoming more and more complex,resulting in more stringent requirements for shield construction technology.How to control the influence of excavation on ground displacement is a huge problem faced by shield construction.As an important construction parameter to maintain the stability of excavation face and reduce the surface displacement,the soil pressure setting has not been clearly calculated and defined so far.Based on the engineering background of Hefei Metro Line 4 underneath Kuanghe shield section,this study explored the setting basis and calculation method of earth pressure by theoretical analysis,and obtained the theoretical solution of earth pressure setting.Midas-GTS finite element simulation software was used to further study the influence of soil bin pressure setting on ground displacement during shield construction,and the numerical solution of soil bin pressure setting was determined.Finally,the theoretical calculation value and numerical simulation value were compared with the actual monitoring data,which verified the correctness of the proposed calculation method of soil bin pressure.The specific conclusions are as follows:（1）By analyzing the disturbance mechanism of soil displacement caused by the setting of soil pressure,the influence of soil pressure on surface displacement is revealed: If the pressure setting of the earth bin is too small,the ground surface will have settlement;The pressure setting of the soil bin is too large,and the surface uplift increases.According to the different shield construction process,the surface displacement is divided into five stages.Based on the existing research and the stability theory of excavation face,this paper puts forward the calculation method of soil bin pressure setting from four aspects: excavation face support pressure,cutterhead extrusion pressure,heading face pressure and soil bin pressure transfer coefficient.（2）Combined with Hefei Metro Line 4 undercrossing Kuanghe River project,according to the proposed calculation method of earth pressure setting,two calculation formulas of earth pressure are used to calculate the earth pressure value of normal construction stage before undercrossing and undercrossing river construction stage.In the normal construction stage,the soil pressure theory of fully eroded soil and the loose soil pressure theory of Terzaghi were used,and the calculation results of soil bin pressure were231.99 k Pa and 112.06 k Pa,respectively.The calculation results of soil bin pressure in the stage of undercrossing the river are 185.92 k Pa and 86.76 k Pa.At the same construction stage,the calculation results of Terzaghi loose soil pressure theory are significantly less than that of the total soil theory.（3）Numerical simulation is used to simulate the shield construction process,and the variation law of surface and river displacement under different soil bin pressures is analyzed.Increasing the soil bin pressure within a certain range can effectively reduce the surface displacement.With the continuous increase of the earth pressure,the disturbance to the soil is intensified,and the surface displacement increases.Finally,by comparing the settlement data,the numerical solution of the earth pressure is obtained.The earth pressure in the normal excavation section is 200 k Pa,and the earth pressure in the undercrossing river stage is 120 k Pa.The influence of shield machine diameter and soil cohesion on soil bin pressure setting is further explored : under the same thickness of overlying soil,the reasonable value of earth pressure setting increases with the increase of shield machine diameter;the increase of soil cohesion has little influence on the setting of soil bin pressure,while the decrease of soil cohesion has great influence on the setting of soil bin pressure.（4）According to the on-site monitoring data,the data of earth bin pressure and displacement of monitoring points during shield excavation are collated and analyzed,and the theoretical calculation,numerical simulation and on-site monitoring values are compared and analyzed to determine the applicability and correctness of the earth bin pressure calculation method.The surface transverse and longitudinal settlement values around the river are sorted out and analyzed,and the surface deformation laws of single-line tunnel and double-line tunnel are obtained.Figure [47] Table [11] Reference [64]...