Abstract:

The boundary and loading device of the physical model of laboratory geogrid pull-out tests are usually rigid, but the boundary conditions of the geogrid in engineering application cannot always correspond to the physical model boundary of laboratory pull-out test. In order to study the effect of boundary conditions on the pull-out test results, this paper uses three-dimensional discrete element method to carry out numerical simulation on the pull-out tests of geogrid-reinforced aeolian sand based on the laboratory triaxial and pull-out tests. The effects of four combination conditions, namely rigid top surface and rigid front wall (R_TR_P), flexible top surface and rigid front wall (F_TR_P), rigid top surface and flexible front wall (R_TF_P), and flexible top surface and flexible front wall (F_TF_P), on the macroscopic and mesoscopic characteristics of reinforced soil interface are studied. The relationship between pull-out force and pull-out displacement, interface shear strength, force chain, porosity distribution and particle rotation law were analyzed under different combination conditions. The displacement of rigid loading plate and flexible boundary particles, the deformation of geogrids under F_TF_P combination, and the evolution law of shear band during pull-out were examined. The results show that the rigid and flexible boundary of the front wall of the model has a great influence on the pull-out force curve pattern and interface friction angle. Under rigid front wall boundary conditions, the pull-out force and displacement curves are machining softening, while the pull force and displacement curves are approximately double-folded under the boundary condition of flexible front wall. When the front wall of the model changes from rigid to flexible, the friction angle of the interface decreases by 7º− 8º. When the normal pressure is less than 90 kPa, it is suggested that the peak reduction coefficients of the F_TR_P combination, R_TF_P combination and F_TF_P combination should be 0.9, 0.6 and 0.7, respectively. In the process of pull-out test, the specimen volumes under the four combinations expand and show dilatancy. The shear band thickness distributions of R_TR_P and F_TR_P are 5.38 and 10.79 times of the medium particle diameter. The shear bands of R_TF_P and F_TF_P have a wider distribution range. The research results are helpful to further reveal the interaction mechanism between geogrid and aeolian sand under rigid and flexible loading modes as well as rigid and flexible front wall boundary.

Key words: pull-out test, boundary conditions, discrete element method, aeolian sand