| With China becoming the second largest economy in the world,the construction of urban subway is in the peak period,and the construction of new shield subway tunnel closely-underneath-crossing the existing subway tunnel is constantly springing up and needs to solve quickly.The construction of the new tunnel destroys the initial stress field and causes the deformation in the soil,therefore the existing tunnels form additional stress and strain.In order to ensurance of operation safety of the exsting tunnel.In order to ensurance of construction safety of the new subway tunnel and operation safety of the exsting tunnel lines,so in the geotechnical engineer area it become an extremely important problem to predict and control of the influence on the exsting tunnels.This paper is on the Kunming Rail Transit Line 4 closely-underneath-crossing the Line 2 and closely-upneath-crossing Line 5.Using Midas GTS/NX to establish the 3D model,and explore the form changes of the exsting tunnels structures in the process of closely-underneath-crossing engineering.The research shows that:(1)Based on the law of shield construction to affect surrounding soil,mechanical mechanism of closely construction and finite element analysis method,establishing the three dimension model which contains the new tunnels closely-underneath-crossing exsting tunnels.Considering the various construction factors such as grouting thickness,supporting pressure of excavation face and grouting material.By analyzed the influence of closely construction on the soil layer,it is concluded that the surface lateral settlement curve conforms to the normal distribution,and the maximum surface settlement gradually increases with construction,which accord the results of previous scholars,thus verify the accuracy of the model.(2)By analyzed the influence of closely construction on existing tunnels.The change of position of the main settlement area on existing Line 2 is from A → B→ D→ A→ F→ H,and the change of position of the main settlement area on existing Line5 is from L → J → I → N → M.At the same time the vertical displacementincreases gradually while the main settlement area and the main uplift area gradually expand.The vertical displacement and axial stress of monitoring points on existing tunnel is increase with the increase of excavation,and amplitude of the vertical displacement and axial stress is maximum when the new tunnel crossing the existing tunnel.The maximun settlement value of the line 2 is 6.6053 mm,and the maximum axial stress is 1255.9400 k N,the maximun uplift value of the line 5 is 7.7715 mm,and the maximum axial stress is 1247.9380 k N.(3)The soil reinforcement is have obviously effect on the deformation of existing tunnels.When keep reinforcement diameter is constant,the vertical displacement of the existing tunnle is decrease with the increase of reinforcement length,when keep reinforcement lengths is constant,vertical displacement of the existing tunnle is decrease with the increase of reinforcement diameters.Among the reinforcement diameters is R5 and the reinforcement length is L5,the minimun settlement value of the line 2 is 3.3186 mm and the minimun uplift value of the line 5 is 4.2432 mm.(4)The grouting thickness,grouting pressure,soil pressure,grouting material(Elastic Modulus and Poisson’s ratio)and construction speed have a great influence for control on vertical settlement the of ground surface,new tunnle and existing tunnels.The reasonable range of grouting thickness is about 0.04 m,the reasonable range of grouting pressure is about 0.35 MPa,the reasonable range of soil pressure is about 0.4MPa,the reasonable range of construction speed is 1 ring.The ground surface,new tunnle and existing tunnels is decrease with the increase of grouting material(Elastic Modulus and Poisson’s ratio),but the effect of chang Poisson’s ratio is not obvious. |
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