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.
