Research Article
Geotechnical Site Investigation and Foundation Characterization for the Legeoda Earth Dam, Dire Dawa, Eastern Ethiopia
Kirubel Molla Bazezew
,
Wahaj Khan,
Belay Sitotaw Goshu*
Issue:
Volume 1, Issue 2, June 2026
Pages:
110-131
Received:
5 February 2026
Accepted:
24 February 2026
Published:
5 March 2026
Abstract: The Legeoda Dam project, proposed in eastern Ethiopia’s Dire Dawa region on the Halo Busa Lege Odamirga watershed, aims to provide irrigation water for downstream agricultural development. This geotechnical feasibility study addresses foundation challenges associated with deep tropical weathering of Oligocene flood basalts overlain by uniform alluvial deposits. Twelve boreholes along the 520 m dam axis, supported by extensive laboratory testing (index properties, shear strength, compressibility, permeability) and in-situ SPT, revealed a consistent stratigraphic sequence: 1.5 m topsoil, 2.5 m clay, 4.0 m sandy silt, 7.0 m highly weathered basalt, 10.0 m fractured basalt, and sound basalt below ~25 m depth. Key findings include uniform overburden thickness (39.9–40.1 m), progressive strength increase with depth (SPT N = 5.5–78.8), high untreated settlement potential (6251 mm), and significant seepage risk through fractured basalt. Seepage, stability, and settlement analyses confirmed technical viability following targeted foundation treatment. Novel contributions include quantitative risk-based treatment optimization and cost-benefit evaluation specific to Ethiopian basalt terrains, demonstrating benefit-cost ratios exceeding 3.0 for integrated cutoff and grouting measures. The study concludes that the site is highly suitable for a zoned earth-rock embankment dam with standard foundation improvements. Recommendations emphasize deep cutoff penetration into sound basalt, selective grouting, and comprehensive instrumentation. This work advances sustainable dam development on flood basalt foundations in rift-margin settings.
Abstract: The Legeoda Dam project, proposed in eastern Ethiopia’s Dire Dawa region on the Halo Busa Lege Odamirga watershed, aims to provide irrigation water for downstream agricultural development. This geotechnical feasibility study addresses foundation challenges associated with deep tropical weathering of Oligocene flood basalts overlain by uniform alluv...
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