Assessing the surface material quality of unpaved rural roads to understand susceptibility to surface deterioration. A case study of four rural areas in KwaZulu-Natal, South Africa

摘要

Road surface deterioration is one of the most common problems of unpaved road networks worldwide. It is a reduction in the performance of a road due to a decline in road surface material quality. Accumulated damage from vehicles, environmental and physical effects may contribute to a decline in the surface material quality and hence deterioration on an unpaved road surface. This study assesses the surface material quality of unpaved rural roads in four rural areas in the KwaZulu-Natal Province, South Africa in order to understand susceptibility to surface deterioration. The study further establishes other possible factors such as slope gradient and rainfall, that could determine the surface material quality. Soil samples were collected from R3, R4, and R5 road classes in four rural areas which are: Emazabekweni, Dukuza, Mkhunya and Mhlwazini Area. Laboratory analyses were conducted in order to determine the performance of the material as potential wearing course. Material performance was then determined using the Standard Methods of Testing Road Construction Materials (TMH 1:1976) classification method. The results obtained imply that there is a need for better material selection during the construction of unpaved road networks. All road classes in Mkhunya, Emazabekweni and Mhlwazini areas exhibited grading coefficient (Gc) values less than 16 and some of the shrinkage product (Sp) values in excess of 365, corresponding to a classification of Class D, A and B. These results indicate material that is susceptible to slippery conditions, easily erodible and prone to the formation of ravels and corrugations. Correlation analysis results conducted to assess the individual relationship between measured rainfall and slope with field shrinkage product and grading coefficient values in each area indicated that variation in slope better explains shrinkage product values in each area with an R-2 of 0.62 when compared to rainfall producing a lower R-2 of 0.57. For grading coeff