Viscoelastic Analysis Of Surface Longitudinal Settlement Caused By Shield Construction Considering Soil Damage

Shield tunnel construction breaks the balance of undisturbed soil,changes the stress state of soil,and causes surface structure deformation,including transverse deformation and longitudinal settlement.The transverse deformation makes the cross section of the tunnel oval rather than the standard circular section.Longitudinal surface settlement will lead to tunnel lining damage,cracking and other problems.From the direction of the shield tunnel,the tunnel is a slender structure along its axis and has great flexibility.Therefore,the study on the longitudinal settlement of the ground surface during shield construction has more reference value.Based on the three parameter viscoelastic model and the improved three parameter viscoelastic damage model,this paper analyzes the surface longitudinal settlement and its proportional relationship caused by shield tunnel construction.The effects of different Overburden Depth and viscoelastic coefficient on longitudinal settlement are comprehensively considered.Combined with the field measured data of surface settlement,the accuracy of the theoretical calculation results is verified.(1)Based on Mindlin elastic solution and three parameter viscoelastic model,the displacement solution of surface longitudinal settlement caused by soil self weight stress,front additional thrust and friction between shield shell and surrounding soil is deduced by Laplace transform and inverse transform.The proportion of various factors causing surface longitudinal settlement in surface settlement is analyzed,which has a good reference value for better determining the composition proportion of surface longitudinal settlement factors,It can provide a theoretical basis for effectively predicting and controlling surface subsidence.(2)Based on the determination of other factors,time and distance variables are introduced to construct a three-dimensional settlement curve,which is convenient to better understand the settlement value of the comprehensive action of each stage and time.The calculation results show that the longitudinal settlement caused by the additional thrust on the front of the shield propulsion is small,while the settlement caused by the friction between the shield shell and the surrounding soil accounts for the vast majority of the longitudinal settlement.Considering the viscoelasticity of soil,the surface longitudinal settlement accounts for about 37% of the total settlement.The research results have certain application value for the settlement control of shield tunnel construction.(3)Considering the soil damage caused by shield construction,the damage variables are introduced based on the soil viscoelastic model,and the effects of different soil cover depths and the changes of various parameters of the three parameter viscoelastic damage model on the surface settlement are analyzed.Therefore,the variation laws of elastic damage and creep damage on the surface settlement are given.Considering the soil damage,the surface longitudinal settlement accounts for about 39% of the surface settlement.Compared with the proportion relationship of viscoelasticity,the consideration is more comprehensive and the calculation is more accurate.