California Bearing Ratio of an Expansive Black Cotton Soil Stabilised with Nano-Silica, Lime and Fly Ash

Abstract

The California bearing ratio (CBR) of a subgrade is the most commonly used measure of its load bearing capacity, and in the expansive black cotton soils found in central India, it is poor. In this paper soaked and unsoaked CBRs of a black cotton soil from Wardha district, Maharashtra for 7 days to 90 days of curing with seven mixes of nano-silica, lime and fly ash are reported. The untreated soil gave a soaked CBR of only approximately 2.4% which is less than the value necessary for a pavement subgrade. Curing for 90 days increased soaked CBR by over ten times with the best mixture (M7) achieving a value of 25.3% and the unsoaked value was nearly 30%. The soaked and unsoaked ratios both increased with the amounts of reagent and the curing times and the ratio of soaked to unsoaked increased as reagent dosage reduced the sensitivity of the soil to soaking. A strong inverse relation between soaked CBR and free swell index confirmed that the strength gain and the loss of expansiveness are two faces of the same process. The treated soil comfortably satisfies subgrade and even sub-base expectations, allowing thinner, more durable pavement sections.