Study On The Influence Of Sheltering Effect And Disturbance Effect On Formation And Pipeline In Twin Tunneling

The subway system presents networked and three-dimensional.Overlapping twin tunnels is a common network form.Commonly,the construction of twin tunnels is not synchronous.The diversity of the layout of twin tunnels and construction sequence leads to complex formation response.Therefore,it is necessary to have a study about the settlement and deformation of ground and pipeline caused by twin tunnels excavation.In this thesis,with the variables of formation loss rate,horizontal and vertical distance between twin tunnels,40 groups of three-dimensional finite element model are established.Comparing with the secondary disturbance of the later tunnel,analyze the influence on the ground and pipeline of the sheltering effect of the upper tunnel in upper-lower excavation sequence and of the disturbance effect of the lower tunnel in lowerupper excavation sequence.Moreover,simple prediction formulas of ground settlement are established,considering the sheltering effect and disturbance effect.The main working contents and results of this thesis are as follows:(1)Based on the relevant centrifugal model test,the sheltering effect and disturbance effect of the tunnel excavated first are introduced in detail.In addition,a kind of three-dimensional finite element model is established to simulate the construction of twin tunnels by displacement control method.The results are compared with relevant centrifuge test results to verify the reliability of the model.(2)Study the influence on ground and pipeline by the excavation of twin tunnels under different layouts and formation loss rates,in upper-lower construction sequence.Establish a prediction formula of ground settlement considering the sheltering effect of the upper tunnel excavated first.When the horizontal distance of twin tunnels is greater than 0.7DT(the DT is the diameter of tunnel),as well as,when the vertical distance of twin tunnels is greater than 1.7DT,the sheltering effect of the first upper tunnel is dominant.At this time,the ground settlement and the pipeline deformation caused by excavation of twin tunnels is smaller.Next,the sheltering index C introduced to the stochastic medium theory to consider the sheltering effect,which lineally decreases with the increase of the horizontal distance between twin tunnels.(3)Study the influence on ground and pipeline by the excavation of twin tunnels under different layouts and formation loss rates,in lower-upper construction sequence.Establish a prediction formula of ground settlement considering the disturbance effect of the lower tunnel excavated first.When the horizontal distance of twin tunnels is smaller than 1.2DT,as well as,when the vertical distance of twin tunnels is greater than 1.0DT,the disturbance effect of the first lower tunnel is dominant.At this time,the ground settlement and the pipeline deformation caused by excavation of twin tunnels is smaller.Next,the disturbance index A introduced to the stochastic medium theory to consider the disturbance effect,which logistically decreases with the increase of the horizontal distance between twin tunnels.(4)When the horizontal distance of twin tunnels is 1.0DT and the vertical distance is 2.0DT,the maximum ground settlement is almost the same in two different excavation sequences.The less settlement of ground and pipeline will be caused in lower-upper sequence,when the horizontal distance of twin tunnels is less than 1.0DT and the vertical distance is less than 2.0DT.On the contrary,the twin tunnels are excavated in upper-lower sequence is better,when the horizontal distance of twin tunnels is greater than 1.0DT and the vertical distance is greater than 2.0DT.