Authors: Ramanuj Singh, Assistant Professor Hariram Sahu
Abstract: Flexible pavements constructed over clay subgrades are highly susceptible to premature distress on account of the low bearing capacity and pronounced moisture sensitivity of clay soils. This paper presents an experimental investigation into the effectiveness of geosynthetic reinforcement in improving the California Bearing Ratio (CBR) of a high-plasticity clay (CH) subgrade collected from Damoh, Madhya Pradesh, India. Two commercially available geosynthetics, a Mirafi HP370 woven polyester geotextile and a Tensar BX1200 biaxial polypropylene geogrid, were evaluated at three reinforcement depths within the CBR mould, namely H/3, H/2, and 2H/3, under both soaked and unsoaked conditions. The soil was classified as CH under IS 1498, with a liquid limit of 55.36%, plasticity index of 30.03%, optimum moisture content of 19.5%, and maximum dry density of 1.69 g/cm³. The unreinforced clay exhibited unsoaked and soaked CBR values of 4.8% and 1.9%, respectively, both indicative of a very weak subgrade. Reinforcement with Tensar BX1200 at H/2 produced the greatest improvement, raising the CBR to 9.6% (unsoaked) and 4.9% (soaked), corresponding to gains of 100.0% and 157.9% over the unreinforced control. The Mirafi HP370 geotextile performed best at H/3, with improvements of 85.4% and 121.1%. The results confirm that both reinforcement type and placement depth significantly influence subgrade performance, and that biaxial geogrid reinforcement at mid-depth offers the greatest structural benefit for the clay investigated. The experimentally derived CBR values are discussed in relation to their implications for flexible pavement thickness design over weak clay subgrades.
