EXPERIMENTAL INVESTIGATION and NUMERICAL ANALYSIS on DEFORMATION CHARACTERISTICS of EXPANSIVE SOIL STABILIZED WITH ENSET FIBER: A CASE STUDY of JIMMA CITY

Abstract

Expansive soils are characterized by significant water absorption, high compressibility, pronounced shrinkage upon drying, and substantial swelling when saturated. These properties pose significant challenges to geotechnical structures. To address these issues, various methods have been employed to enhance the engineering properties of expansive soils prior to their use in construction. This study evaluates the efficacy of enset fiber as a stabilizing agent for expansive soils through experimental investigations and numerical analyses. The research commenced with the characterization of the mechanical properties of expansive soil in its natural state, focusing on shear strength, and deformation behavior. Laboratory testing was conducted according to the standards set by the American Association of State Highway and Transportation Officials (AASHTO) and the American Society for Testing and Materials (ASTM) to assess the impact of enset fiber content on the geotechnical properties of the soil. Utilizing the finite element method (Plaxis 2D), the study analyzed the deformation characteristics of the expansive soil after stabilization with enset fiber. Soil samples were collected from two distinct pits in Jimma city, and various of laboratory tests were performed, including natural moisture content, grain size distribution, specific gravity, Atterberg limits, free swell, modified Proctor, California Bearing Ratio (CBR), one-dimensional consolidation, and triaxial tests. The samples were stabilized with enset fiber at ratios of 0%, 0.25%, 0.5%, 0.75%, 1%, and 1.25%. Results indicated that at an optimal enset fiber content of 1%, the liquid limit values decreased from 90.9% to 49.3% and from 94% to 49.9% for samples S1 and S2, respectively. The plasticity index also showed significant improvement, reducing from 54.2% to 9.4% for sample S1 and from 59% to 10.3% for sample S2. The optimal moisture content (OMC) for modified compaction improved from 30% to 15% for sample S1 and from 31% to 21% for sample S2. Maximum dry density (MDD) increased from 1.36 g/cm³ to 1.49 g/cm³ for sample S1 and from 1.35 g/cm³ to 1.45 g/cm³ for sample S2. CBR results at the optimal enset fiber content improved from 1.3% to 8.7%, it improved by 569.23% for sample S1 and from 1.14% to 8.2%, it improved by 620.18% for sample S2. Numerical analysis revealed that deformation was reduced from 719.9 mm to 135.5 mm, deformation reduced by 81.1% and from 794 mm to 207.8 mm, deformation reduced by 73.7% for sample S1 and sample S2, respectively. This study underscores the significant potential of enset fiber as an effective stabilizing agent for expansive subgrade soils. The experimental results demonstrate that the incorporation of 1% enset fiber substantially enhances geotechnical properties, leading to notable reductions in liquid limit and plasticity index, thereby improving workability and stability. Additionally, the findings indicate significant increases in maximum dry density and CBR, critical parameters for pavement construction. Finite element analysis confirms these laboratory results, affirming that enset fiber treatment effectively mitigates deformation under loading conditions. Overall, this research highlights the viability of enset fiber as a sustainable and economical solution for enhancing the performance of expansive soils. Future research should investigate the long-term effects and optimal application techniques of enset fiber specifically for mitigating issues related to expansive soils across different soil environments.