| Rapid urbanization in our nation has caused subway construction to become increasingly prevalent in cities in recent years.In the process of tunneling of subway shield tunnel,it is easy to cause settlement damage to the soil layer,especially in the composite stratum.The mechanical parameters of the two kinds of soil are quite different,and the stress state and deformation and settlement characteristics of the soil layer are difficult to control,so the prediction of the formation settlement and deformation caused by tunnel construction will be more complicated.Therefore,it has great significance to study the deformation and settlement rule of shield tunnel construction in gravel,sand and mudstone composite stratum.Based on this,this paper takes the tunnel project of Nanchang Metro Line 4 as the engineering background,adopts the method of indoor model test and numerical simulation to study the influence of shield tunnel construction on the formation settlement rule under the condition of gravel,sand and mudstone composite stratum.The main research contents and achievements are as follows:(1)Based on particle image velocimetry(PIV)technology,laboratory model tests were carried out.With tunnel depth and composite formation ratio k(the height of gravel sand layer within the tunnel diameter/the height of mudstone layer within the tunnel diameter)as variables,under the condition of composite formation,The settlement and deformation of soil layers at different depths,the soil settlement at the tunnel vault and the variation law of the width i of settlement trough caused by shield tunnel construction.The results show that: for the settlement law of surface soil,the buried depth of the tunnel is fixed.The smaller the k value is,the smaller the settlement value of the surface soil layer is,and the width of the settlement trough is also smaller,from the maximum1.5D(tunnel diameter)to 0.5D.With a certain k value,the smaller the tunnel buried depth,the deeper the sag of the surface settlement trough curve,and the curve changed from "wide flat type" to "thin type",that is,the surface settlement increased continuously,with the maximum increase of 53.29%.When the tunnel buried depth is constant,the soil settlement value at the tunnel vault decreases with the decrease of k value.If k is constant,the smaller the tunnel buried depth is,the larger the soil settlement at the tunnel vault is.The settlement values of different depth soil layers were extracted,and the peck formula was used to fit the settlement curve.Finally,the prediction formula of settlement trough width i under different rock span ratio(rock span ratio = the thickness of overlying soil layer/tunnel diameter)and different k values was derived.The relationship between i and the depth h from the tunnel horizontal axis to the stratum was linear.(2)PLAXIS3D software was used to conduct modeling analysis on the formation settlement deformation law caused by shield tunnel construction under different tunnel depth and different composite soil ratio.The results show that: for the subsidence law of the surface soil layer,the larger the tunnel buried depth is,the greater the tunnel construction disturbance to the overlying soil layer,the worse the stability of surrounding rock,the larger the subsidence value of the surface soil layer,the larger the subsidence trough area,and the larger the width of the surface subsidence trough.With a constant value of k,the maximum surface settlement decreases with the increase of tunnel depth,while the affected area of the surface increases with the increase of tunnel depth.For the soil settlement at the tunnel vault,the larger the value of k,the greater the disturbance of tunnel construction on the soil settlement at the tunnel vault,and the worse the stability of surrounding rock at the tunnel vault.When the value of k is between 1 and 0.5,the surrounding rock at the tunnel vault has the best stability.With a certain value of k and the increase of the tunnel buried depth,the smaller the soil settlement at the vault,the larger the range of the settlement failure transmitted to the surrounding area.The closer the tunnel is to the surface,the larger the width range of the settlement trough,the settlement trough is "wide flat type".The smaller the tunnel depth is,the smaller the width of the settling trough is,and the settling trough is "slender".The deeper the tunnel is,the thicker of the soil layer above the tunnel,the better the self-stability and the stronger the resistance to damage deformation.The deeper the tunnel is,the thicker of the soil layer above the tunnel,the better the self-stability and the stronger the resistance to damage deformation.When the soil layer is disturbed by the tunnel construction,the smaller the settlement value generated by the surface.(3)The settlement values of different depths in the numerical model were extracted and compared with the settlement data of the model test.The settlement deformation rules of the two are in good agreement,which can prove the rationality of the numerical simulation data.With the increase of soil depth,the larger the subsidence of the corresponding soil layer,the narrower of the sedimentation trough.The width of the sedimentation trough mainly ranges from 2D to 3D.The peck formula was used to fit the settlement curve,and the corresponding settlement formula was obtained.According to the parameters in the fitting formula,the prediction formula of settlement trough width under different rock span ratio and different composite formation ratio could be deduced. |
PDF Full Text Request