Viscoelastic Analysis And Reliability Study Of Ground Surface Settlement Of Shield Tunnel

During the construction of shield tunnel,the disturbance of surrounding soil will inevitably be caused,which will result in the change of stress state of soil,and then produce ground surface settlement,which will endanger the normal use of adjacent buildings and underground pipelines.Therefore,it is necessary to analyze and control the ground surface settlement of shield tunnel effectively.The study of long-term settlement of shield tunnel in soft soil is inseparable from the study of constitutive relationship and rheological behavior of the underlying soil.The factors affecting the surface settlement are uncertain.The reasonable selection of viscoelastic model and the correct analysis of the uncertainty of influencing factors are undoubtedly of great significance to the influence of shield tunnel ground surface settlement.In this paper,a three parameter solid viscoelastic model is selected to analyze the ground surface settlement of shield tunnel.In addition,considering the randomness,fuzziness and grey of the variables,the reliability of ground surface settlement of shield tunnel is studied.Considering the viscoelastic characteristics of soil,based on the Mindlin solution,the three-dimensional viscoelastic solution of shield tunnel surface settlement is presented by using the three-parameter solid viscoelastic model and Laplace transformation.Based on the calculation and analysis of engineering examples,it is obtained effects of ground surface settlement that considering viscoelasticity,viscosity coefficient,distance from excavated surface,excavation depth to face friction of cutter head,side friction of cutter head,The influence of frontal additional thrust and friction between shield shell and surrounding soil on surface settlement.Considering the randomness and fuzziness of the factors affecting the surface settlement,the membership function is introduced,and the fuzzy random reliability calculation formulaof the ground subsidence caused by the tunnel construction is established by using the first-order second-moment center point method and the checking point method.Carry out calculation and analysis.The results show that for the same allowable maximum settlement,the randomness and fuzziness of the variables are not considered.The reliability index calculated by the center point method is larger than that by the design point method,and with the increase of the allowable settlement,the reliability index calculated by the center point method and the design point method are both increasing,which is consistent with the engineering practice.The reliability index obtained by design point method considering the influence of randomness and fuzziness is decreasing.Considering the grey property of variables in the calculation of structural reliability,combining the first-order second-moment method,the grey first-order second-moment central point method and the gray first-order second-moment design point method are given,and the randomness and fuzziness of the variables are considered.The reliability analysis method of shield tunnel ground surface settlement considering the randomness,fuzziness and gray of variables is given,and the calculation and analysis are carried out with concrete examples.The reliability of the ground surface settlement of shield tunnel is compared with that of the shield tunnel which only considers the grey calculation of variables.The calculation results show that the reliability index calculated by design point method is larger than that of center point method if only the grey property of variable is considered under the same allowable settlement.When grey variables are considered only,with the increase of allowable settlement,the reliability indexes calculated by the center point method and the design point method all show an increasing trend consistent with the engineering practice.The results show that in the reliability analysis of shield tunnel surface settlement,the appropriate reliability method should be used to calculate the reliability index according to different conditions.