EVALUATION OF INDEX PROPERTIES OF BLACK COTTON SOIL STABILIZED WITH SOYA BEAN HUSK ASH

Abstract

The objective of this study was to assess the index characteristics of black cotton soil stabilized with Soybean Husk Ash (SBHA). The black cotton soil used in the study was obtained from the Gamadadi region of Borno State, Nigeria. The Atterberg limit test was conducted to determine the liquid limit, plastic limit, plasticity index, and linear shrinkage. In addition, sieve analysis was carried out. The soil was classified as CH (clay of high plasticity) under the Unified Soil Classification System (USCS, ASTM 1992) and as belonging to the A-7-6(0) group under the AASHTO (1996) classification system. When conditions change from wet to dry, the soil color appears grayish-black. The index properties of the soil showed that the liquid limit was 52%, which decreased to 46% at 16% SBHA. Similarly, the plastic limit decreased from 19.52% to 16.37% at 16% SBHA. This occurred because higher-valence cations replaced weakly bonded ions in the clay, resulting in particle flocculation and the release of absorbed water. As a result of pozzolanic reactions and clay dilution, the plasticity index decreased from 32.48% to 29.63%, indicating reduced clay activity and improved soil stability. At 16% SBHA, the specific gravity decreased from 2.63 to 2.38 and the shrinkage limit decreased from 22.86% to 14.29%. While the Optimum Moisture Content increased from 18.41% to 24.54%, the Maximum Dry Density decreased from 1.68 g/cm³ at 0% SBHA to 1.58 g/cm³ at 12% SBHA and then slightly increased to 1.59 g/cm³ at 16% SBHA. To improve the index properties of black cotton soil, an optimum SBHA content of 12% is recommended.