Research On The Constitutive Model And Settlement Prediction For Deep Soft Soil Under Metro Moving Load

With the development of China’s transportation construction,the metro has become the most important traffic tool of urban traffic.During the operation,metro moving load would produce vibration,which could cause deformation along tunnel axis,settlement along metro foundation,and then lead to crack of tunnel lining,structural crack,seepage and pavement settlement,which would impact the safe operation of the subway,the usage of all structures along the metro lines,as well as bring serious noise pollution to the environment.Therefore,the problem about metro-induced vibration,has become an important research topic in the design and operation maintenance.Based on the above issues,it is necessary to further research on dynamic characteristic and settlement.It provides theory and engineering bases for design,construction and maintenance of metro engineering.The deep soft soil of the Yangtze River Delta is taken as the research object,considering the creep characteristics of soft soil,and the characteristics of low amplitude load is studied.The main research work and results are as follows:(1)Considering the impact of factors:dynamic stress amplitude,effective confirming pressure,frequency and the natural water content of soil,variable load and variable frequency,then the GDS dynamic triaxial test was performed,the dynamic parameters VS.vibration times curve was analyzed,the dynamic shear modulus function considering vibration times was established;Based on the pseudo-static method,using the Mesri model,the strain curve was analyzed under low amplitude dynamic load,then the concept of stable vibration times was put forward by the experimental results,which could establish theoretical bases for prediction of long-term settlement;Meanwhile,the dynamic pore water pressure normalization curve was analyzed.(2)Do the applicability analysis on the critical state soil mechanics under dynamic conditions.Deriving and comparing the differences between plastic theory and the bounding surface model;Discussing several methods of rheological theory;Based on the low amplitude characteristics of metro moving load,considering creep characteristics of soft soil under long-term dynamic load,using pseudo-static method,the Mesri creep model and Taylor model was introduced in the bounding surface model,and the time-dependent bounding surface model was established.(3)The principle of the ABAQUS subroutine was analyzed,then based on the establishment of time-dependent bounding surfacemodel,using implicit Euler integral algorithm and stop strain method optimize the program;The parameters of constitutive model were given from the GDS dynamic triaxial,and the relationship and the affects of the parameters were analyzed.Subsequently,the validity of the constitutive model was verified.(4)Combined with the experimental analysis and the finite element method,a power function was proposed to predict the settlement under dynamic load with high vibration times.Establishing a metro vibration simplified model,then the metro vibration load was calculated by empirical formula;Subsequently,the 2-D metro finite element simulation was presented,the metro vibration load and the established constitutive model were embedded,setting up visco-elastic artificial boundary,predicting settlement by the proposed power function formula,comparing calculations with the test values.The results showed that the proposed method was reasonable and feasible.Furthermore,the sensitivity of the tunnel buried depth,speed,axle load of the metro was analyzed,and the settlement was selected as evaluation index.Meanwhile,a 3-D finite element model was established,the settlement along the longitudinal,at different horizontal position and depth were obtained.