Factors Affecting Erosion in Unpaved Roads

Abstract

More than 90% of the road network in 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 rain. In addition to rainfall duration and intensity, findings were that the key factors that affected soil erosion in earth roads were soil type, clay content, soil plasticity, particle size distribution and degree of the surface layer compaction as well as traffic loading and speed.

Calibration of the Simple Rainfall Simulator for Investigating Soil Erodibility in Unpaved Roads

“…These were chosen deliberately based on IDF curves from countries of the Central and Eastern Africa, a region in the Sub-Saharan Africa where about 80% of the road networks are unpaved [9], [12][13][14] and thus in much need to control erosion in these roads. Using the flour method to determine the size of the raindrops [3], [7], [15][16][17], the drop sizes of 3 mm, 3.2 mm, and 3.5 mm were found, leading to the kinetic energy from the raindrops of 193.5 µJ, 244 µJ and 301.1 µJ, respectively for 30 mm/hr, 51 mm/hr and 68 mm/hr rainfall intensities. The sizes of the raindrops were satisfactory to initiate erosion of soils of 0.4 mm < D50 < 1.5 mm [18], which were found appropriate at the surface of unpaved roads [9].…”

“…According to [1], [3], [7], [17], [30], the useful coefficient of uniformity (CU) -measure of consistency of raindrops spatial distribution must be in the range of 80% to 100% for acceptable performance of a rainfall simulator. This coefficient is known as the Christiansen coefficient as the researcher introduced it first in 1942 [3].…”

“…An additional diagram for the detachment of the soils by surface flow velocity with respect to the particle size distribution of the soils was given according to Carey and Simon [31], as shown in Figure 10. The tested soils were synthesized by mixing gravelly sandy (GS) and very gravely sandy (VGS) soils with percentages of English china clay (ECC) to simulate the variability of soils at the surface of unpaved roads in terms of particle size distribution as well as the required plasticity index at the surface of unpaved roads of about 2% to 12% [7,9,32], as shown in Table 3.…”

“…The use of rainfall Intensity -Duration -Frequency (IDF) curves for different regions can help to check the accuracy of a rainfall simulator. Deliberately, the example IDF curves from the Central and Eastern Africa region (Democratic Republic of Congo and Rwanda) [4][5][6] which could represent the natural rainfall intensities and drop sizes in Sub-Saharan Africa, and probably in most of the tropical region where unpaved roads are predominant were used [7]. Table 1.…”

Modelling the Effects of Soil Properties, Rainfall and Road Geometry to Erosion in Unpaved Roads

“…For example, it is about $400 million in Java (Indonesia) and more than $1500 million in Zimbabwe, which certainly is beyond the affordability of these countries. Also, it is worth noting that unpaved roads are about 80% of the road network in the developing world [12]- [13], [15]- [16]. Therefore, they cannot be fully paved with asphalt or concrete any time soon, and their importance to the development will remain vital by providing access to education, health, market, and job services to mention a few.…”