Abstract
The Arba Rekete-Gelemso gravel Road section is affected by the presence of expansive soil, this soil has shrinking and swelling behavior due moisture fluctuation. The main objective of this research work is to investigate the Characterization of Borrow materials for embankment fill and capping layer based on their index and strength properties for Road Construction of the proposed route. In order to achieve the objectives, field investigation and nine (9) samples were also collected from the identified borrow area and laboratory test analysis were performed such as, Atterberg limits, compaction, CBR and percentage of swell tests. ERA‘s and AASHTO’s standard technical specifications have been used to interpret the data by integrating the field with laboratory test results. The subgrade soil of route, having liquid limit value greater than 60% and plastic index value greater than 30% and CBR value less than 5%, at Chainage km 0+000-4+000, 5+900-8+000, 9+400-12+900, 13+500-14+000, 15+000-16+000, 17+100-17+600, 18+500-20+500, 21+500-34+900, and 35+200-47+000 unsuitable. The index and strength properties of the borrow materials fulfill the requirement for embankment fill and subgrade improvements. Finally, all unsuitable subgrade soil along the study route corridor are recommended to remove and replace with suitable and non-expansive subgrade materials, since enormous amount of selected fill materials that fulfill the requirements for subgrade soils improvement are available nearby the study area.
Highlights
In Ethiopia, several rural road constructions have been carried out
Borrow materials are vital for embankment, capping layer and improve the subgrade soil and resist the load that imposed on the subgrade
The weathered to decomposed rock material which are suitable for embankment fill and capping layer have been used as borrow sources where the natural sub grade material soil is poor to improve the strength of the subgrade soil
Summary
Road construction activities increased from year to year, geological and geotechnical or engineering geological assessment was not given an attention for the road project, because of less emphasis given to the engineering geological investigation most of the constructed road prematurely failed. Good road construction are absolutely essential in order to provide goods and services to populations in remote villages, for administration purposes, for movement of agricultural products to larger cities, and for education and health programs of rural and urban peoples Geological and Geotechnical investigation and characterization of sub grade soil is important component for the design and construction of road. In Arba Rekete –Gelemso road section, there is no detailed geological and geotechnical investigation that have been conducted before. The proposed road section has been upgrading to asphaltic road, so prior to the construction, the subgrade soil has to be properly investigated to ensure the suitability for road construction.
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