Discrete Element Analysis Of Biaxial,Direct Shear And Pulling Tests Of Geogrid-Sand-clay Layered Reinforced Structure

In practice,due to the infiltration of rainwater and the influence of groundwater,the water content of the filler changes greatly,it will have important influence on the friction angle and cohesion of the clay and clay reinforced structure,which may cause certain safety hazards.In order to ensure the reinforcement effect of clay fillers,some scholars have proposed a geogrid-sand-clay layered reinforced structure.Sand layer can be laid between the geogrid and the clay,and uses the good drainage characteristics of the sand,the clay reinforced structure can maintain long-term stability because of the friction characteristics and good drainage characteristics of the granules.However,due to the precision of the instrument,the mechanism of the sand layer is not clear.Therefore,the numerical simulation test of the biaxial,direct shear and drawing is carried out on the geogrid-sand-clay layered reinforced structure.The key factors such as sand layer thickness,confining pressure and vertical pressure are fully considered.Based on numerical simulation test,microscopic research is carried out on different working conditions.The main research results include:(1)A numerical biaxial tests simulation of the sand-clay layered structure and geogrid-sand-clay layered reinforced structure was conducted to assess the cohesion and internal friction angle of structures.The simulation results show that laying the sand layer can increase the internal friction angle of the structure and reduce the structural cohesion.High confining pressure can increase the bearing deviatoric stress.(2)A numerical direct shear test simulation of the geogrid-sand-clay layered reinforced structure was conducted.Extract the maximum and minimum main stress,cracks,porosity,displacement to analyze the microscopic characteristics of the structure under different direct shear displacements and different sand layer thicknesses.The effect of laying a sand layer on the mesoscopic properties of the structure was investigated.The results show that,after the sand particles are laid between the clay and the reinforced materials,during the shearing process,due to the friction of the sand,the displacement ofclay near the sand layer differs in different area,the cracks increases,and the clay particle displacement in the near sand layer is relatively small,the main stress of the left half of the box increases,and the main stress of the right half of the box decreases.With the increase of the thickness of the sand layer,the constraint of the sand on the displacement of the nearby particles firstly increases and then decreases.Compared with the unlayed sand layer,the maximum principal stress of the left half box increases,the maximum principal stress of the right half of the box is decreased.(3)The pull-out test simulation of the geogrid-sand-clay layered reinforced structure was conducted.Extract the maximum and minimum main stress,cracks,porosity,displacement to clarify the microscopic effects of the ribbing drawing on the structure under different sand thickness and different drawing displacements.The results show that,after the sand layer is laid between the clay and the reinforcement,in the process of pulling the reinforcement to the left,the displacement field forms a closed circle,the cracks in the clay soil gradually appears ‘x' shape,the soil near the ribs undergoes dilatancy,the principal stress of soil in the left half box increases,the principal stress of soil in the right half box decreases.When sand particles are laid between the ribs and the clay,the principal stress of the soil near the ribs decreases,and the principal stress in other areas decreases.