Macroscopic And Mesoscopic Study On Geogrid Pullout Tests Under Rigid And Flexible Top Boundary Conditions

The geogrid pullout test is considered by many scholars as an important research method to reveal the mechanical behavior of the interface between reinforcement and soil.At present,the rigid and flexible top boundary conditions are often used for the normal load in the pullout test.However,there are certain disputes about the top boundary conditions used in the standard pullout test.The influence of the pullout test on the top boundary conditions is unclear.This article combines indoor experiments and discrete element numerical simulation to study the interaction mechanism of reinforcement and soil under rigid and flexible top boundary conditions.The mechanical response and deformation behavior of the geogrid and soil under the two top boundary conditions are explained in depth from the macro and meso level.This article expounds the coupling effect of the normal load and the fill height on the pullout test results under the condition of the rigid top boundary from the macro level.It is concluded that when the fill height is small(h=10 cm),the normal load has a greater impact on the pullout test results;with the gradual increase of the fill height,the influence of the normal load on the pullout test results gradually decreases,but the difference in the influence of the normal load still exists.When the normal load is small(σn=25 k Pa),the fill height has a greater impact on the pullout test results;with the gradual increase of the normal load,the fill height gradually reduces the impact on the pullout test results.When the normal load σn=100 k Pa,the influence of the fill height on the results of the pullout test is negligible.This article analyzes the influence of the fill height and the number of transverse ribs on the pullout test under the rigid and flexible top boundary conditions from the meso level.The results show that: when the pullout displacement is small,the rigid and flexible top boundary conditions have almost no effect on the pullout test results;with the increase of the pullout displacement,the influence of the top boundary condition on the pullout test results becomes gradually obvious.The pullout force under the rigid top boundary condition under the same pullout displacement is slightly larger than that under the flexible top boundary condition.The particle flow software reveals the vertical displacement distribution law of particles at the top boundary of the pullout test box,the distribution law of earth pressure inside the sample and the variation law of the internal coordination number of the sample,the distribution law of the front wall lateral force,and the distribution law of tension and strain of geogrid,the distribution law of contact force between soil particles inside the sample,and the distribution law of displacement field of reinforcement and soil particles inside the sample,intuitively shows the influence of the fill height and the number of transverse ribs on the interaction between reinforcement and soil under different top boundary conditions.Based on the above research,the results of this article are expected to provide a certain reference value for the design of reinforced soil structures and provide a certain reference basis for the optimization of test methods.