African Geotechnical Engineering is a peer‑reviewed scholarly journal published under the Pan‑African Research Journals (PARJ) platform, advancing African‑centred and global research.
Slope Stability Analysis of Road Embankments in the Mountainous Terrain of Eastern Equatoria, South Sudan
Road embankment failures in the mountainous terrain of Eastern Equatoria, South Sudan, represent a persistent threat to regional connectivity, humanitarian access, and economic activity in one of sub-Saharan Africa's most geotechnically challenging environments. The region's steep escarpment terrain, deeply weathered tropical soils, intense monsoon rainfall (1,200–1,800 mm/year), and near-total absence of site investigation data have historically resulted in embankment designs based on empirical rules-of-thumb with no formal factor of safety analysis. This study presents the first systematic slope stability assessment of road embankments along five critical routes in Eastern Equatoria (Torit–Kapoeta, Nimule–Juba, Kapoeta–Narus, Chukudum–Budi, and Lafon–Moli corridors), encompassing 28 embankment cross-sections identified as unstable or potentially unstable through field reconnaissance. Geotechnical characterisation included Standard Penetration Tests (SPT, n = 86 boreholes), laboratory triaxial and direct shear tests, and soil classification per USCS. Slope stability was analysed using the Bishop Simplified Method and Spencer's Method within the Slide2 software package, for both dry-season and post-rainfall saturation conditions. Results indicate that 61% of assessed embankments have Factors of Safety (FS) below the critical threshold of 1.25 under post-rainfall conditions, with five sections recording FS < 1.0 (indicating active or imminent failure). A rainfall-triggered pore water pressure model calibrated to local piezometer data reveals that embankment FS drops by 28–45% within 48 hours of a 100 mm/day rainfall event. Stabilisation recommendations including geosynthetic reinforcement, drainage improvements, slope regrading, and soil nailing are evaluated through par
Copyright (c) 2023 African Geotechnical Engineering
Low-Volume Road Design Using Laterite and Stabilised Soils in South Sudan's Equatoria Region
Low-volume roads constitute over 85% of South Sudan's rural road network and are the primary means by which farming communities in the Equatoria Region access markets, healthcare, and educational institutions. Despite their importance, these roads are largely constructed without reference to engineering design standards, using locally available laterite and gravelly soils whose suitability and geotechnical behaviour under tropical loading conditions are poorly characterised in the published literature for this specific geographic context. This study presents a comprehensive geotechnical and pavement engineering investigation of laterite and stabilised soils from three borrow areas in Central, Eastern, and Western Equatoria States, aimed at developing practical design guidelines for low-volume road construction using local materials. Forty-two soil samples were collected and subjected to physical, mechanical, and chemical characterisation, including particle size distribution, Atterberg limits, compaction, California Bearing Ratio (CBR) at 0, 7, 28, and 90-day curing intervals, X-Ray Fluorescence (XRF) geochemical analysis, and free swell. Stabilisation trials were conducted with hydrated lime (2–8%), ordinary Portland cement (2–8%), and rice husk ash (2–8%) to evaluate improvement in CBR and plasticity reduction. Accelerated loading trials at a field wheel-track facility assessed rutting performance over a simulated 3,000 × 10³ ESAL loading history. Results indicate that natural laterites from Equatoria meet the minimum CBR threshold for unsealed base course (CBR ≥ 80%) in two of three borrow areas after moisture conditioning, but all three require stabilisation to serve as a structural subbase above weak subgrade soils. Cement stabilisation at 4–6% produces the highest
Copyright (c) 2017 AJE-GeotechE https://creativecommons.org/licenses/by/4.0/