Comparative analysis of improved soaked CBR values in local subgrade soil using geogrid and fiber reinforcement

Subgrade soil's California Bearing Ratio (CBR) is vital in flexible pavement design. As per IRC SP-72-2015, soaked CBR values between 7–9 indicate “good” quality, while 10–15 reflect “very good” quality. Improving CBR from “good” to “very good” can reduce pavement thickness by 15.8% for traffic up to 2 million standard axles, which is especially beneficial for hill roads due to cost and carbon footprint savings. The present study focusses on upgrading local Jammu soil (CBR = 7.27%) to the “very good” category using geogrid of strength(55kN/m) and polypropylene fibre reinforcement. Single-layer geogrids (placed at H/3 and H/2) improved CBR to 8.76%, while a double-layer (top and bottom) reached 12.3%. A modified mould with a tension rod enhanced geogrid performance. Incorporating 0.25% polypropylene fiber (12 mm) yielded a CBR of 15.5%. The results confirm that both double-layer geogrid and fiber reinforcement significantly enhance subgrade strength, enabling pavement thickness reduction and sustainable construction.