Comparative Evaluation of Different Aperture Geogrids for Ballast Reinforcement through Triaxial Testing and Discrete Element Modeling

Geogrids are commonly used in transportation applications for stabilization and reinforcement due to their higher tensile strengths compared to geotextiles as well as the stiffness improvement they provide through arresting and interlocking granular particles in the geogrid apertures. Influenced by many factors, such as the aperture shape and size of geogrid, the degree of interlocking contributes significantly to the reinforcement benefit of geogrid for improving the performance of any geogrid reinforced system. This paper describes recent research efforts at the University of Illinois focused on conducting permanent deformation testing of geogrid reinforced ballast specimens using a large-scale triaxial test device. Two different geogrids with rectangular and triangular aperture shapes respectively were evaluated for reinforcement benefit of cylindrical specimens compacted and prepared with ballast size uniformly graded aggregate materials. To further investigate the geogrid reinforcement mechanisms, an aggregate image-aided numerical modeling approach based on Discrete Element Method (DEM) was also adopted with the capability to create actual ballast aggregate particles as three-dimensional polyhedron elements having the same particle size distributions and imaging quantified average aggregate shapes and angularities. Preliminary results from both laboratory experiments and DEM simulations indicated that geogrids with triangular apertures performed more effectively in arresting particle movements through improved interlock.