Estimation of Unsaturated Soil Characteristics And Shear Strength of the Compacted Clay Soil of the Maga Earthfill Dam Using Physical Properties

Abstract

Tropical soils of the Sub-Saharan area mainly include expansive clay soils and are widely used as compacted materials in geotechnical applications such as earthfill dam construction in the Far North of Cameroon. Since the unsaturated properties of expansive soils are highly related to their physical properties, the present study investigated unsaturated soil property estimation based on their physical features through the existing estimation model equations. Data from twelve (12) compacted soil specimens were obtained and used to carry out predictions of unsaturated soil variations along with the entire suction range (0 kPa–106 kPa), for the main drying process. The soil-water characteristic curve (SWCC), shrinkage curve, permeability and diffusivity coefficient functions, water storage capacity, void ratio and incremental and total strain variations were estimated over the entire suction range and water content variations. The model equations by Fredlund and Xing, Brooks and Corey, Gardner and Fick’s law were used for SWCC and volume–mass unsaturated property estimation. Two (2) samples with different fine content, i.e., different plasticity, were particularly considered for a drying path simulation. It was found that predicted incremental and total volumetric deformations increase with a decrease in the degree of saturation. According to simulation results, air-entry occurrence and a net stress increase in compacted specimens under unsaturated conditions appear to contribute to their shear strength value. Estimation results from most of the estimation models used generally show an increase in shear strength for low (wet state) to medium suctions and a decrease for higher suctions (dry state). Physicals properties-based correlations models, for estimation of SWCC parameters have been then proposed. Predictions obtained from the models used were compared with experimental data and the test results of the literature. There was a good agreement. The results obtained in this paper provide another way of understanding the physical and mechanical behavior of the expansive clay soils of the Sub-Saharan area and constitute a simple and powerful tool for geotechnical engineers in the soil behavior of geotechnical man-made structures in unsaturated conditions, at initial phases or along an entire engineering project.