Investigating Causes of Gravel Roads Deterioration: A case of West Showa Zone

Abstract

In Ethiopia Gravel roads are serving majority of the nations in rural areas for agricultural, commercial and other social mobility purposes. Unpaved roads deteriorate faster than paved roads because they are more susceptible to environmental factors and have a lower construction cost. The objective of this study was to identify factors cause deterioration of gravel road in West Shoa Zone. A comprehensive literature concerning the factors of road deterioration, common road defects and their causes were investigated. The primary data were gained from visual inspection through field survey and laboratory test while the secondary data have been collected from administrative agencies and from construction firm or consultant firms. The investigation were involved through field survey and laboratory testing on those projects to determine the bearing capacity of sub grade soil and natural gravel surfacing course based on ERA standards and project specifications. The drainage conditions and deterioration types on the road segment were collected through field survey. The study was adopted purposive sampling techniques to sample the gravel road section materials. The sampling procedures were done by selecting at least from three places for both normal section and severely damaged sections. Data collection process was carried out by obtaining necessary data from the design documents and the laboratory test for subgrade soil and gravel wearing course materials that were collected from the site. The methodology were carried out in laboratory experimental test procedures of ASTM, AASHTO, ERA, and other low volume road standard specification method. The maximum value of dry density measured during the field test for subgrade compaction was 82.92% MDD, which is less than 95% MDD.similarly, The maximum value of dry density measured during the field test for surfacing compaction was 90% MDD, which is less than 95% MDD. The Atterbergs' limit test of subgrade soil expresses the type of soil is A-4 up to A-7, and the value of CBR test results falls between 3 and 7, indicating that the subgrade soil is very weak and does not fulfill the requirements. It was discovered that the causes of gravel road deterioration in those selected road sections were primarily due to very low bearing capacity of subgrade soils, poor compaction methods, water intrusion into subgrade, lack of side drainage, and improper installation of structures such as pipe culverts and slab culverts. This research offers providing proper drainage and reconstructing the crown or camber formation at the deteriorated sections to solve those problems.