Numerical Modelling of Geogrid-reinforced Unpaved Roadways: Fid-Bau Portal

Numerical Modelling of Geogrid-reinforced Unpaved Roadways

Huang, Wen-Chao / Liao, Hung-Yun

The main reinforcing mechanisms of the geogrid reinforced unpaved roadway include (1) tensile effect of the geogrid, (2) aggregate interlocking and lateral restraint, and (3) enhanced compaction of the aggregate material. In this study, the mechanical performance of using geogrid reinforcement in an unpaved roadway was discussed through numerical modeling including finite element method and discrete element method. The conclusions are below: (1) Finite element analysis indicates that in an unpaved roadway, the settlement measured at the surface of the aggregate layer comes from the deformation of the aggregate layer and subgrade layer; however, most of the surface settlement comes from the settlement of the subgrade layer. (2) Finite element analysis indicates that the shear stress at the interface of the aggregate and the subgrade material is similar for the unreinforced case. However, for the reinforced case, the shear stress became smaller at the subgrade side of the geogrid reinforcement compared to the shear stress at the aggregate side of the geogrid reinforcement. This indicated that the difference is compensated by the geogrid reinforcement and the induced shear stress in the subgrade layer subsequently decreased. (3) Discrete element analysis indicates that from the resultant contact forces recorded below the loading plate when comparing the unreinforced and reinforced cases, an approximate 50% increase of contact force to reach similar plate settlement is required for the reinforced case. Therefore, the local stiffness of the reinforced case was increased significantly when geogrid reinforcement is added. What was meant by local stiffness is that for reinforced case, most of the increased contact forces between particles were located right below the loading plate, only in the area below the loading plate and close to the geogrid reinforcement can we find the enhanced area extended slightly outward. (4) Discrete element analysis indicates that when checking from the movements of the particles, it is found that in the reinforced case, the aggregate particles tend to move within a limited range in the area under the loading plate both horizontally and vertically. Due to the assumption that the geogrid (which is consisted of unmovable particles) has very high stiffness, the aggregate particles are stuck (interlocked) in the apertures of the geogrid with very minor lateral deformation. When interlocking of aggregate material and geogrid aperture is formed at the interface, progressive interlocking between aggregate particles is initiated such that an enhanced confinement effect of the aggregate layer is appeared. The above condition explains that a higher resultant contact force may be required to reach similar plate settlement in the reinforced case.