Numerical stability analysis on the selected reservoir slopes of Ajima Earthen Dam, Central Ethiopia

This study presents a comprehensive stability analysis of specific reservoir slopes at the Ajima Chacha Earthen Dam in Ethiopia, aiming to enhance the understanding of stability conditions under varying hydrological scenarios, both dry and wet. The stability assessments consider the inherent properties of slope materials, comprising both rock and soil. To facilitate this analysis, extensive field investigations were conducted alongside laboratory tests to gather critical data pertinent to the stability assessments of key slopes vulnerable to failure from multiple triggering mechanisms. Factors identified as predisposing these slopes to instability include surface water infiltration, weak geological formations, steep gradient angles, and high degrees of weathering in the slope constituents. The finite difference method was employed as the numerical framework for analyzing the selected critical slopes. Utilizing FLAC2D (Fast Lagrangian Analysis of Continua in Two Dimensions), the stress–strain response of the slope stratigraphy was meticulously examined, leading to the computation of safety factors for a two-dimensional slope model. Notable deformations were recorded in the soft rock units and the highly weathered materials within the slope profiles. The analysis revealed a concerningly low safety factor during wet conditions for the assessed slopes. Critical reservoir slopes (RS-1, RS-2, RS-3) have (1.32 1.24), (1.42 1.12), and (1.63 0.99) under dry and wet slope conditions respectively. The results from the numerical modeling of the reservoir slopes provide crucial insights for monitoring slope integrity, particularly in sensitive zones. These insights are essential for the long-term stability management of dam reservoir slopes, enabling the implementation of effective mitigation measures to ensure the safety and reliability of the dam infrastructure.