Research On Surface Settlement Caused By Shield Tunnel Construction

During the construction of a shield tunnel,it is inevitable that it will cause disturbance to the soil around the tunnel,break the original equilibrium state of the soil,and cause ground settlement above the tunnel.Excessive ground settlement will cause damage to buildings around the tunnel,ground roads,and underground pipes,and seriously threaten the lives and property of the people.In this paper,based on the research on the shield tunnel between Baiyun Culture Square and Yunxi Park Station of Line 12 of Guangzhou Rail Transit,the related research on the ground settlement deformation caused by shield tunnel construction under cohesive soil conditions is presented.The main research contents are as follows:(1)Through a lot of reading of professional books and scientific research papers on shield tunnel construction,the theoretical analysis of ground settlement caused by shield tunnel construction was carried out.The main causes of surface subsidence are obtained: formation loss and consolidation settlement;five stages in the surface settlement process: initial settlement,excavation surface settlement,tail settlement,tail pore settlement,and long-term continuous settlement;control of surface settlement is summarized Major engineering measures.(2)The finite difference software FLAC3 D was used to simulate the construction process of the shield tunnel,and the deformation law of the ground settlement of the clayey soil layer was obtained.The surface horizontal settlement curve is similar to the normal distribution curve.After the advance tunnel excavation is completed,the maximum ground settlement is located on the ground directly above the axis of the advance tunnel,and the maximum ground settlement is 12.73 mm.After the completion of the subsequent tunnel excavation,the maximum ground settlement is located directly above the centerline of the two tunnels.The maximum ground settlement is 21.83 mm,the maximum ground settlement is38.87 mm,and the maximum uplift of the ground is 30.66 mm.It meets the requirements of monitoring and measurement specifications and can provide areference for engineering construction.(3)The finite difference software FLAC3 D was used to numerically simulate six influencing factors on palm surface thrust,shield tail grouting material strength and grouting amount,grouting pressure,tunnel centerline horizontal distance,and tunnel excavation method.The elastic modulus and grouting pressure of the grouting material of the shield tail have a great impact on the ground settlement.The grouting amount,the thrust of the palm surface,and the horizontal distance of the centerline of the tunnel have a secondary effect on the ground settlement.The tunnel excavation method has the following effects on the ground settlement.The effect is relatively small.At the same time,a suitable palm surface thrust of 200 k Pa,a modulus of grouting material of 2 MPa and above,a grouting layer thickness of 20 cm to 25 cm,and a grouting pressure of 0.2 MPa to 0.3 MPa were obtained at the shield section of Baiyun Culture Square to Yunxi Park Station.(4)Analyze on-site monitoring measurement data and compare the monitoring measurement data with the results of numerical simulations.It is found that the curve of the ground horizontal settlement tank obtained from the two data basically matches,and the change trend is basically the same.The maximum difference between the ground settlement amount is less than 2 mm,which verifies the accuracy of the numerical simulation.