| In order to investigate the impact on the surrounding environment caused by shield tunneling in compound stratum formed by land reclamation which generally contains a silt layer,this thesis relies on Shenzhen Airport North Station to Shenzhen Airport Station interval shield project of SuiGuan-Shen inter-city railway to conduct the research.First,the existing research results were summarized to establish the theoretical basis on analyzing ground displacement caused by shield tunneling.Second,the shield tunneling parameters and the displacement data of ground surface were analyzed in a comprehensive way.Finally,an analysis framework centering on the loss rate of ground was established,and a finite element model was built to simulate the construction of shield tunnel,through which the influence on the ground settlement and the internal force of the surface structure layer were analyzed.Major results are as follows:1)The jacking speed is positively correlated with the screw conveyor speed.The driving speed is equal to the product of penetration rate and rotating speed of cutter.Reduction of penetration rate within a certain range can reduce the cutter wear.However,to maintain the same jacking speed at this time,the rotating speed of cutter must be increased.Chamber pressure increases with the soil pressure.And chamber pressure is controlled by the jacking speed and screw conveyor speed,but there is no linear relationship between the three parameters.Total thrust increases with chamber pressure.2)When the shield enters the flight zone of the airport,the grouting volume increases.After the grouting volume being increased,the disturbance to the ground due to excavation and the ground addition caused by grouting jointly control the vertical displacement of ground surface.The former makes the surface have a trend of continuous settlement,the latter gives the surface a rebound(or uplift)trend,the two factors work together,causing the subsidence and resilience of the ground settlement;with the passage of time and the distance increasing,both of the influence are weakened,finally reaching the balance,and the surface displacement achieves stability.3)Natural surface and surface structure are influenced by shield construction.Distribution of settlement can be described by Gauss curve.Within a certain range,settlement increases linearly with the loss rate of ground,and the value of inflection point increases firstly and decreases then,and the ratio of settlement tank volume to actual ground loss volume increases with the loss rate of ground and gradually approaches a certain value.Shear-shrinkage properties of silty soil layer can slightly increase the maximum ground surface settlement,but significantly increase the inflection point value of the surface subsidence tank,thus increasing the volume of the subsidence tank.Presence of surface structural layer can reduce the maximum subsidence by 20% and increase the inflection point value.4)There is a good linear relationship between the maximum settlement and the loss rate of ground,as well as the internal force of the surface structure layer and the loss rate of ground.The analysis framework centering on the loss rate of ground can be used to calculate the magnitude of the internal force of the structure layer by using the ground surface settlement data.The current shield tunneling monitoring program may neglect a part of ground surface settlement that could cause over 60% of maximum surface subsidence and more than 30% of structural stress to be underestimated.5)The excessive grouting during shield tunneling will lead to the increase of the volume of the ground,causing the uplift of the surface.The development and distribution of the surface uplift are affected by the diffusion of slurry.According to the direction of the slurry diffusion,distribution of the surface uplift can be divided into three modes,as center bump mode,two side offset mode,and one side offset mode. |
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