Modified AASHTO method for design of geogrids reinforced flexible pavements

The modified AASHTO method of reinforced flexible pavements has recommended the use of geosynthetic material in reinforcing the base course road. The use of the modified AASHTO method for the design of geogrid-reinforced flexible pavements was studied. Three soils were used: fine sand, silty and clayey. River Bed Material was used in the subbase layer and Water Bound Macadam was used for the base course. Two types of geogrids were used to reinforce the pavement layers. Compaction tests were conducted to determine the maximum dry density and the optimum moisture contents for subgrade soils and the base and subbase materials. Cyclic triaxial tests were conducted on unreinforced and reinforced samples of subgrade soils, subbase and base materials. California Bearing Ratio (CBR) tests were conducted on subgrade soils only. Correlations between the resilient modulus and CBR soils were examined. The resilient modulus was determined for subgrade, base and subbase with and without reinforcement and the structural layer coefficient for each layer was determined. The results showed that including geogrids in the subgrade, subbase or base course could reduce the thickness of these layers.