A THESIS SUBMITTED TO THE FACULTY OF HYDRAULIC AND WATER RESOURCES ENGINEERING, WATER TECHNOLOGY INSTITUTE, SCHOOL OF GRADUATE STUDIES, ARBA MINCH UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENT OF THE DEGREE OF MASTER OF SCIENCE IN HYDRAULIC ENGINEERING

Abstract

The evaluation of dam safety is paramount for ensuring the structural integrity and operational reliability of embankment dams. Dam failure can have severe consequences, including flooding, property damage, and environmental impacts. This study examines the effects of rainwater infiltration on the stability of the Khalid Djido embankment dam, located in the central Ethiopia region with high rainfall intensity and frequency. The dam’s stability was assessed using numerical modeling techniques, with PLAXIS 2D employed for coupled stress pore water pressure analyses under various rainfall scenarios. The Soil Conservation Service (SCS) Curve Number (CN) method estimated infiltration rates at 3.12 mm/hr. Complementarily, an Intensity-Duration-Frequency (IDF) analysis determined a 24-hour rainfall intensity of 3.18 mm/hr using precipitation data from 1990-2021. These hydrological inputs, combined with stability analyses, provided a comprehensive assessment of the dam’s response to various rainfall scenarios. The analysis revealed significant variations in pore pressure within the dam, with maximum and minimum values of 34.07 KN/m² and -381.8 KN/m², respectively. High negative pore pressures indicate potential zones of tension. The downstream toe region was identified as a critical area susceptible to high pore pressures and potential stability issues. Elevated pore pressures were found to significantly reduce soil shear strength, leading to increased deformations and a heightened risk of slope failure, particularly in the downstream slope and core regions. To assess dam stability, a factor of safety (FoS) analysis was conducted using the strength reduction method. The calculated FoS values ranged from 1.1 to 1.51, with lower values indicating increased risk of instability. While the dam exhibited adequate stability under certain conditions, the analysis revealed critical scenarios where the FoS approached unity, particularly during rainfall events. These findings underscore the importance of effective drainage systems and monitoring to mitigate potential risks posed by rainwater infiltration. This research contributes valuable insights to dam safety knowledge and water resource management in regions susceptible to rainfall-induced instability.