Improvement in Subgrade CBR Values of Low-Volume Rural Roads Using Geogrid: Experimental Investigation

The strength of the subgrade is crucial for determining the thickness of pavement layers, and the California bearing ratio (CBR) value is a key parameter for such consideration. A stronger subgrade can reduce the design thickness of contributing layers, making road construction more cost-effective. However, in many rural areas, the quality of the subgrade used for low-volume unpaved roads may not be as per the Codal requirements due to poor geological settings. In such cases, upgrading the subgrade’s strength becomes essential to ensure the longevity and durability of rural roadways, facilitating better access and mobility for local communities. This paper experimentally investigates the effect of geogrid reinforcement in improving the CBR value of a poor-quality subgrade material collected from the vicinity of the IIT Jammu campus. An initial soaked CBR test on the local soil yielded a CBR value of 3.5%, categorizing it in the ‘poor category’. To improve the soaked CBR of the soil, geogrid was placed in single, double, and triple-layer configurations within the soil in the CBR mold. The geogrid was uniformly tensioned around the edges in each configuration. The experimental results demonstrate a notable enhancement in the soaked CBR value of the subgrade, resulting in reduced total pavement thickness. Specifically, an improvement of 10%, 14.2%, and 35.7% was observed with the single-layer, double-layer, and triple-layer configurations, respectively. Consequently, a 24.7% reduction was obtained in the required pavement thickness calculated for traffic conditions of 450 cvpd in rural areas according to the IRC SP-20 [9]. Additionally, a considerable improvement in the resilient modulus was observed when geogrid layers were included in the local subgrade soil.