Geotechnical and geophysical studies for the cause of landslide in Lesalso, Laelay Maichew Wereda, northern Ethiopia

The northern highlands of Ethiopia often experience slope failures triggered by rainfall. Landslides are common in Lesalso, Laelay Maichew Wereda, northern Ethiopia, causing destruction to homes, crops, agricultural lands, the death of wildlife, and the eviction of local residents from their homes. The primary objective was to identify the causative and triggering factors for the landslide occurrence. Field investigations, soil laboratory test, vertical electrical sounding (VES) and profiling were conducted. The landslide affected area is characterized by aphanitic basalt with small agglomeratic basalt, phyllite, laterite sandstone, metachert and rhyolite rock units. Physical and engineering properties of 22 soil samples indicated that the failure materials mainly consist of fine grain soils (72.72 %), liquid limit (29.5 %–66.4 %) and plasticity index (7.6 %–43.65 %), medium to high degree of swelling (0.08 %–71.5 %), variable low to high water content (21 %–54.3 %), specific gravity (2.45–2.81), dry unit weight (1.467 g/cm3 to 2.254 g/cm3), activity of soils (0.379 %–1.78 %), soil compression index (0.1785 %–0.43685 %), shrinkage index (0.27 %–28.61 %), shrinkage limit (0.062 %–30.86 %), friction angle (ϕ) (7.68°–47.94°) and cohesion (C) (6.45 kPa–52.72 kPa). The primary factors influencing slope stability include the severely weathered and impermeable rocks beneath the hard and fractured surface, the presence of fine grain soils (clay and silt), a geohydrological setting that facilitates the accumulation of water pressure within the slope, and a steep slope that can generate sufficient stress to induce failure. These findings provide critical insights for the development of proactive mitigation strategies to protect local communities and infrastructure from landslide hazards.