Using Geogrids to Minimize Reflective Longitudinal Cracking on Pavements over Shrinking Subgrades

Texas has the most extensive network of surface-treated pavements in the United States. This network has suffered from the detrimental effects of changing environmental conditions and expansive soils in the subgrade since its deployment. Longitudinal cracking is one the most prevalent pavement distresses caused by volumetric change of the expansive subgrade. Preliminary practice showed that geogrids can be used as reinforcement to reduce the reflection of longitudinal cracking on the pavement over shrinking subgrades effectively. However, little is known about the mechanism leading to propagation of the longitudinal cracks to the surface of the pavement, and accordingly, the benefit of using geogrid treatment has not been properly quantified. The stress field and constitutive models of the subgrade soil subjected to matric suction change were evaluated. Fracture mechanics theory was used to analyze the crack propagation in the pavement and the mechanism of the geogrid reinforcement. A finite element model was developed to simulate the crack in the pavement and to estimate the stress intensity factor at the crack tips. The benefit of using geogrids was quantified by comparing the stress intensity factors of the crack in the pavement with and without a geogrid. Results showed that geogrids can significantly reduce the stress intensity factor at the crack tip in the pavement; this indicates that the desiccation cracks in the subgrade are less likely to propagate through the base layer toward the pavement surface. The geogrid with higher stiffness provided marginal additional reinforcement to the pavement structure.