Abstract
Flexible pavements constructed over weak subgrades with a California Bearing Ratio (CBR) range of 2-4 % are subjected to premature failure owing to excessive stress and deformation. Their performance is significantly influenced by the actual contact tire pressure. These problems can be addressed using geogrid reinforcement. In this study, the impact of tire contact pressure on geogrid-reinforced flexible pavements built over weak subgrades was examined using physical models with a (1/3) scale. Five pavement sections were tested: control (unreinforced), which consists of three layers wearing asphalt layer of 5 cm, a bituminous base of 6 cm, subbase layer of 9 cm, all resting on a weak subgrade of clay soil of 50 cm. The reinforced sections were biaxial and triaxial geogrid reinforcement at the subbase-subgrade interface, and at the middle of the subbase course layer. Repeated axle loads were applied at three directly measured tire contact pressures (480, 560, and 690 kPa). Vertical stresses were measured at the bottom of the asphalt layer and the top of the subgrade. Increasing the tire pressure from 480 to 690 kPa raised the vertical stresses at the asphalt bottom by 67% in the control section and by 56% in the reinforced sections. At the top of the subgrade, the same increase resulted in vertical stress rises of 42 % for the control section and 32 % for the reinforced sections. Geogrid reinforcement reduced vertical stress at high pressures effectively, with subbase-subgrade reinforcement showing better performance than reinforcement at the middle depth of subbase. However, reinforcement with a triaxial geogrid presented good performance under different tire contact pressures. where the geogrid reduces stresses at the bottom of the asphalt layer by 28% and 23% for the biaxial and triaxial geogrids, respectively, when used at the subbase-subgrade interface, while the geogrid reduces stresses at the top of the subgrade layer by 49% and 43% for the biaxial and triaxial geogrids, respectively. The results revealed that tire pressure is a fundamental factor that affects flexible pavement performance, especially when built over weak subgrades, whereas geogrid reinforcement could further contribute to better performance.