Effects of Soil Properties and Geogrid Placement on CBR Enhancement of Lateritic Soil for Road Pavement Layers

Abstract

The mechanism for strength development when unbound soils are reinforced with geogrid is not well understood. Research on geogrid reinforcement has tended to focus largely on improving the properties of the geogrid with little attention to the influence of soil properties on geogrid performance. This study investigated the effects of plasticity index and gradation properties of lateritic soils on strength enhancement within a soil-geogrid-reinforced composite for a pavement. Three samples of soil with different plasticity and gradation were compacted and tested in strength with and without geogrid reinforcement. Reinforcement involved incorporating one and two layers of geogrid into the sample at different depths within the compacted sample height. The effect of reinforcement, plasticity index and grading on strength enhancement of the compacted material was measured by CBR for soaked and unsoaked conditions. The results indicated that as soil plasticity increased, the CBR decreased. In addition, as the proportion of coarse aggregate particles in the soil increased, the CBR of the reinforced soil increased for all geogrid placement locations. Two-layer geogrid reinforcement only marginally improved strength over single layer reinforcement placed close to mid-depth of compacted sample. This seems to suggest that in some cases, single-layer rather than multiple-layer geogrid reinforcement may suffice provided the placement depth is appropriate.