Research On Dynamic Bearing Capacity Of Seasonal Flooding Subgrade

As Chinese economy grows,especially the strategy of "transportation power ",Chinese enterprises have more cooperation in transportation construction with tropical regions such as Southeast Asia and Africa.For the seasonal flooding area,the rainfall is large and concentrated,and the precipitation will infiltrate into the roadbed along the slope,which will change the distribution of pore pressure,moisture content and dry and wet state of the roadbed,affecting the bearing capacity and stability of the subgrade.The purpose of this study is to analyze the seepage characteristics inside the subgrade,the waterproof and drainage effect of various protective measures,and to recommend reasonable layout suggestions.Finally,using Finite Element Model system to analyze the attenuation law of modulus after drying and wetting cycle in the subgrade of pavement structure,to determine the equivalent elastic modulus of subgrade,and to provide reference for engineering construction.First of all,this paper expounds the theory of unsaturated soil and designs the experiment of filter paper by combining theory with practice.According to the relationship between moisture content and suction rate of Whatman No.42 standard filter paper,then the corresponding values of moisture content and matric suction of 7test points were obtained to fit the parameter values in the soil-water characteristic curve model for further study of subgrade seepage field.Secondly,the periodic change of water level is assumed by combining with the existing meteorological data in this area,and to realize the periodic change by DISP subroutine,which is mainly used to customize the boundary conditions of specified degrees of freedom,such as displacement,pore pressure,temperature,etc.The Finite Element Model was established to analyze the influence of pore pressure,velocity and moisture content on the external water level.Then,the model of subgrade and pavement structure with waterproof and drainage measures was established respectively to make a comparative analysis of the protection effect of slope protection,drainage cushion and underground seepage ditch on subgrade.Then,according to the constitutive factors of modulus of resilience,the reflection index of drying and wetting cycle is proposed.Compiling UMAT subroutine considering drying and wetting cycle through USDFLD subroutine which achieve material properties associated with field variables defined in the Abaqus/CAE.The drying and wetting cycle test of the sample is designed,and the parameters in the modulus of resilience constitutive are fitted by the indoor dynamic triaxial test results,and the influencing factors of the elastic modulus are analyzed at the same time.Lastly,the modulus attenuation law is analyzed by extracting the results of the characteristic month and the water level change of the representative unit.At the same time,for the equivalent value of modulus,it is necessary to establish the mechanical response model of pavement due to the different modulus of the whole subgrade.According to the method of determining the effective resilient modulus in the AASHTO,the equivalent resilient modulus of the whole year is calculated by the monthly equivalent resilient modulus,which provides a reference for the value of the resilient modulus of the flooding subgrade in the road design.