Spatial-Time Evolution Mechanisms Of Ground Settlement Due To Shield Tunneling In Complex Layer

With the development of society,the proportion of urban rail transit construction is increasing year by year.As one of the rail transportation modes,subway is mainly build in the urban center with complex layer.When the shield tunneling method is widely used,the ground surface will sink or uplift due to the different layer conditions.As a result,the safety performance of the surrounding environment will decrease.Therefore,it is necessary to study the mechanisms of spatial-time evolution of the surface settlement caused by shield tunneling in complex layer.Based on the engineering background of a section of Wuhan Metro,the complex layer are divided into complex geological and complex underground structure.This paper mainly study the shield interval time and spatial evolution mechanism of surface settlement.And ground surface settlement is obtained under complex geological conditions of interval distribution.As well as the complex underground structure in spatial distribution regularity of ground surface settlement type is also obtained.Specifically,there are the following findings and conclusions:(1)When the shield tunneling passes through the red clay area,the surface settlement value is large due to the weak bearing capacity of the red clay.The time and spatial evolution mechanism of the region is closely associated with the passage of the tunnel face.Basically,the surface settlement value of the tunnel face before passing through is small,the settlement value increases significantly after the tunnel face passes,the accumulative settlement value gradually tends to be stable after the tunnel face is far away,and the daily settlement value tends to zero.Therefore,the bearing capacity of the soil layer should be improved after the tunnel face passes.(2)When the shield tunneling passes through the limestone area,the surface settlement value of the observation point group is larger where the bearing capacity of the formation is weak,while the surface settlement spatial curve of the observation point group where the tunnel is located in the soil layer anisotropy is generally irregular.In the region at the same time,it is concluded to be six interval,which of ?,?,? has obvious mechanisms of time and spatial evolution,similar to the red clay area.The interval ? has only one set of observation points,and there is no obvious mechanisms of spatial-time evolution.The largest number of observation points in intervals are III and ?,only 46%?47%of the observation points show significant spatiotemporal evolution.(3)When the shield tunneling passes through the complex underground structure area,the spatial evolution mechanism is not significant because of the influence of the complex structure.The surface settlement value in this section is small,and the surface settlement value of the right line is generally larger than the left line,but the excavation of the right line will lead to further settlement of the left line by 0.5mm?1mm.At the same time,it is affected by different locations of the observation points,so the significance of spatial evolution mechanism is also greatly different.(4)In this paper,the time evolution mechanism of each measuring point group in complex underground structure is closely related to its spatial mechanism.After analysis,this paper studies four types of settlement tanks successively:typical settlement tank,partial regular settlement tank,irregular settlement tank(left and right lines)and data missing section settlement tank.Following this order,the time evolution of daily settlement and accumulated settlement rule gradually changed from obvious to inconspicuous.It can be seen that the time evolution mechanism of each measuring point group can be predicted according to the classification of its space curve.