Deformation Analysis of Black Cotton Soil Stabilized with Brick Dust and Lime for Subgrade using Finite Element Method: A Case Study of Jimma City

Abstract

Expansive soils are those in which the addition or removal of water has resulted in a large volume change. Due to its swell and shrink when subjected to seasonal change, expansive soil presents a significant challenge when buildings are constructed on it. Black cotton soil is an expansive soil. This expansiveness is not good for any construction that is built on it. Therefore, this expansive soil needs improvement to increase its bearing capacity. Therefore, this study aims to improve the soil-bearing capacity and deformation analysis of stabilized black cotton soil. Deformation analysis is done by the finite element method. This finite element method is a numerical technique used to solve problems in engineering. The finite element method is widely used in civil engineering to analyze structures such as bridges, buildings, road subgrades, dams, and others. Plaxis 2D is a finite element software used to analyze the deformation in road subgrade. The laboratory tests were done according to the American Association of State Highway and Transport Officials (AASHTO) and the American Society for Testing and Materials (ASTM).The laboratory tests were done on natural moisture content, specific gravity, grain size distribution, the Atterberg limit test, modified compaction, the California bearing ratio, and the triaxial test. This sample was stabilized with a ratio of 0%, 4%, 8%, 12%, and 16% of brick dust and 0%, 1%, 3%, 5%, and 7% of lime with soil, respectively. The result of the laboratory test at the optimum percentage of 12% brick dust and 5% lime shows that the liquid limit values improved from 93.2% to 67.5% and 87.5% to 66.5% for samples 1 and 2. Plastic limit results improved from 48.71% to 58.2% and 41.15% to 55.91% for samples 1 and 2, respectively. The soil is classified under high clay (CH) as per the unified soil classification system (USCS) and A7–5 as per the American Association of Highway and Transport Officials (AASHTO). After improvement, the soil is classified as MH as per the USCS system and A-2-7 as per AASHTO. The optimum ratio for improved modified compaction at 12% brick dust and 5% lime was improved from 26.76 to 18.5% and 31.5% to 22.5% for samples 1 and 2, respectively. Maximum dry density: 1.42 g/cm3 to 1.58 g/cm3 and 1.43 g/cm3 to 1.55 g/cm3. The California bearing ratio test at 2.54mm penetration is 1.29%, 10.6%, and 1.12% to 9.85% for samples 1 and 2, respectively. The deformation analysis result shows that at the optimum percentage of stabilizing agent, the characteristics of virgin soil were improved from 2.087*10^-3m to 0.9734*10^-3m for sample 1 and 2.928*10^-3m to 1.032*10^-3m for sample 2, respectively. The effect of the improvement of brick dust and lime on black cotton soil was studied. This was done for the stabilized black cotton soil to check the improvement. The optimum reduction in deformation was obtained at 12% brick dust and 5% lime. Therefore, brick dust-lime-soil stabilization shows the promising improvement of expansive subgrade soil. The long-term impacts of environmental conditions, such as moisture content and temperature change, on stabilized soil should be taken into account when doing the deformation analysis. This will help in evaluating the durability and sustainability of the stabilization technique.