ABSTRACT
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.
