THE PERFORMANCE OF MARGINAL GRAVEL MATERIALS USED FORSURFACING GRAVEL ROADS: A CASE STUDY OF IRINGA REGION

Abstract

This study on the performance of marginal gravel materials employed as surfacing materials for gravel roads was done by monitoring existing gravel roads surfaced with marginal gravel materials in Iringa region. Four gravel roads surfaced with marginal gravel materials in Iringa region were randomly selected in order to obtain empirical results that have general application in Iringa region and those regions experiencing the same climatic (moisture and temperature) seasons. To reduce the cost, the research was linked with existing gravel roads surfaced with marginal gravel materials. A minimum number of six and maximum of eight trial sections of 300 m length on each selected gravel road were established and monitored for a period of three years (2011-2013 inclusive). The performance was measured and quantified in terms of distress noted during condition survey with particular reference to gravel loss. The gravel loss and type of distress prevalent on trial sections were correlated with average daily traffic volume, marginal gravel material’s physical characteristics, and climate. The measurement of gravel loss was based on optical levelling, while that of distress was done through visual inspection. Tests on marginal gravel materials comprised of grading and Atterberg limits. The study came out with a gravel loss prediction model. It was noted that, the rate of gravel loss and distress noted on each trial section depended on the quality of construction, maintenance input, daily traffic volume, material’s physical characteristics, and the geological type of marginal gravel materials used as the wearing course. Careful selection of marginal gravel materials at the source and appropriate maintenance methodology addressing attributes of distress is necessary to obtain satisfactory performance of the gravel roads networks in Tanzania. Finding of the study can be used with other findings in similar studies conducted in Tanzania to draft appropriate local marginal gravel materials specifications for surfacing gravel roads which should then be subjected to more empirical study for fine tuning.