Vol. 11 No. 3 (2026)
Low-Volume Road Design Using Laterite and Stabilised Soils in South Sudan's Equatoria Region
Abstract
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
Read the Full Article
The HTML galley is loaded below for inline reading and better discovery.
How to Cite
Keywords
Research Snapshot
Desktop reading viewReferences
- Akuoc, J.M. and Deng, A.M. (2019) "Engineering properties of lateritic soils from Central Equatoria State, South Sudan, for road construction." East African Journal of Engineering, 6(1), pp. 12–24.
- AASHTO (1993) Guide for Design of Pavement Structures. Washington DC: American Association of State Highway and Transportation Officials.
- Colla, C., Gabrielli, E. and Milani, G. (2017) "Shrinkage cracking in cement-stabilised sub-bases: a review." Road Materials and Pavement Design, 18(1), pp. 22–48.
- CSIR — Council for Scientific and Industrial Research (2002) Technical Recommendations for Highways: TRH 20 — The Structural Design, Construction and Maintenance of Unpaved Roads. Pretoria: CSIR.
- De Graft-Johnson, J.W.S. and Bhatia, H.S. (1969) "The engineering characteristics of the laterites of Ghana." Proceedings of the 7th International Conference on Soil Mechanics and Foundation Engineering, Mexico City, Vol. 2, pp. 13–43.
- Ekwulo, E.O. and Drummer, D.B. (2009) "Fatigue and rutting strain analysis of flexible pavements designed using CBR methods." African Journal of Environmental Science and Technology, 3(12), pp. 412–421.
- FAO — Food and Agriculture Organization (2022) South Sudan Agricultural Market Assessment: Road Access and Post-Harvest Loss Survey. Rome: FAO.
- Gidigasu, M.D. (1976) Laterite Soil Engineering: Pedogenesis and Engineering Principles. Amsterdam: Elsevier.
- Ingles, O.G. and Metcalf, J.B. (1972) Soil Stabilization: Principles and Practice. Sydney: Butterworths.
- Kuot, P.R., Akuoc, J.M. and Gai, L.M. (2021) "Geotechnical assessment of gravel materials for rural road construction in Eastern Equatoria, South Sudan." African Journal of Geotechnical Research, 4(2), pp. 34–46.
- Little, D.N. (1999) Evaluation of Structural Properties of Lime Stabilized Soils and Aggregates. Arlington, VA: National Lime Association.
- Mitallib, M.O.A. and Bankole, S.A. (2011) "Stabilization of sub-base material using rice husk ash and cement." International Journal of Engineering Research and Technology, 4(8), pp. 1–9.
- MoRB — Ministry of Roads and Bridges, South Sudan (2022) South Sudan Road Network Inventory and Condition Survey. Juba: MoRB.
- MoRB — Ministry of Roads and Bridges, South Sudan (2023) Unit Cost Database for Road Infrastructure in South Sudan. Juba: MoRB.
- Monismith, C.L., Ogawa, N. and Freeme, C.R. (1975) "Permanent deformation characteristics of subgrade soils due to repeated loading." Transportation Research Record, 537, pp. 1–17.
- Mugume, R.B. and Kalumba, D. (2016) "Investigating the use of rice husk ash as a soil stabilizer in road construction in Uganda." Geotechnical Engineering for Infrastructure and Development, pp. 2761–2766.
- Netterberg, F. (1994) "Calcretes and other pedocretes as pavement materials in Southern Africa." Proceedings, 7th Conference on Asphalt Pavements for Southern Africa, pp. 1–13.
- Ola, S.A. (1983) "Geotechnical properties and behaviour of some stabilized lateritic soils." Quarterly Journal of Engineering Geology, 16(4), pp. 305–310.
- Oyetola, E.B. and Abdullahi, M. (2006) "The use of rice husk ash in low-cost sandcrete block production." Leonardo Electronic Journal of Practices and Technologies, 8, pp. 58–70.
- Paige-Green, P. (1989) "The use of marginal and non-standard materials in road construction." Proceedings, Annual Transportation Convention, Pretoria, 2(1), pp. 1–34.
- Pinard, M., Greening, P. and Hongve, J. (2018) TRL Overseas Road Note 31: A Guide to Road Surface Dressing in Tropical and Sub-Tropical Countries. 3rd edn. Crowthorne: TRL Limited.
- SATCC — Southern African Transport and Communications Commission (1998) Low Volume Sealed Roads: Design and Construction Guidelines. Midrand: SATCC.
- Sherwood, P.T. (1993) Soil Stabilization with Cement and Lime. London: HMSO.
- Yoobanpot, N., Jamsawang, P. and Chaiyaput, S. (2017) "Mechanical and microstructural properties of soft clay stabilized with cement and calcium carbide residue." Applied Clay Science, 141, pp. 146–156.
- World Bank (2022) South Sudan Infrastructure Sector Assessment 2022. Washington DC: World Bank Group.
- © 2025 African Geotechnical Engineering. All rights reserved. DOI: 10.XXXXX/age.2025.1114
- Conversion notesMessage(type='warning', message='An unrecognised element was ignored: {http://schemas.openxmlformats.org/officeDocument/2006/math}oMathPara')