Esdras Ngezahayo, Michael P.N. Burrow, Gurmel S. Ghataora

Abstract: More than 90% of the road network in rural areas of the developing countries is unpaved and comprises of either gravel or earth roads. Such roads are prone to erosion leading to the formation of potholes, rills and gullies. Many studies have been undertaken on soil erosion, but only a few are focussed on earth roads. A systematic analysis of research on erosion of soils in earth roads was undertaken to draw out lessons that can be learnt. 564 studies were assessed. Of these only 85 were relevant to earth roads. Most significant erosion driver was total rain, rainfall duration and intensity. Further findings were that the key factors that affected soil erosion in earth roads were soil type, clay content, soil plasticity, and particle size distribution; degree of the surface layer compaction, and traffic loading and speed. To challenge and validate the findings of the literature, the main factors affecting erosion were controlled during laboratory erodibility tests of a sand soil mixed with its 0%, 5%, 10%, 15% and 20% china clay and of a granular subbase material. The soils were compacted at their maximum dry densities and subjected to a simulated rainfall intensity of 30mm/hr for 30 minutes, and at 0% and 6% slopes. Interestingly, laboratory results agreed with the literature. Erodibility increased with increase in rainfall duration and slope gradient. In sand – china clay mixes, erodibility reduced with increased clay content. An increment of 5% china clay corresponded to a reduction of eroded sediment of about 8% to 12%. The subbase soil material was very less erodible due to its robust particle size that resisted detachment due to rain drops. Moreover, it was observed that most soils were detached and eroded within the first 15 minutes of the rainfall after which detachment reduces.

Keywords: Unsurfaced roads, erosion, erodibility, erosion factors, erosion rate

Date Published: December 5, 2019
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