Engineering Geological Characterization And Suitability Analysis Of A Subgrade Soil A Case Study On Selected Section Of Ambo Wolisso Road Project South Western Ethiopia

The performance of a pavement is highly controlled by the underlying roadbedrnsoil geotechnical characteristics. A subgrade provides support for upper layers ofrna pavement structure that are constructed upon it and the traffic load. Thernpurpose of geotechnical characterization of a subgrade is to evaluate the quality ofrnthe subgrade based on various results of insitu and laboratory test and soundrngeotechnical principles that would impact the pavement performance.rnIn the present study the subgrade soils are characterized on selected section ofrnAmbo-Wolliso road located in south western Ethiopia, Oromia region. Therngeographic location of the study area is bounded by UTM coordinate of 80 56’ Nrn370 52’ E and 8049’ N 37053’ E. the objective of the study were 1, to characterizernthe subgrade material based on the engineering geological parameters 2, to assessrnthe suitability and bearing capacity of the subgrade soil 3, to suggest somerncounter measures for the unsuitable part of the subgrade soil.rnTo achieve this objective, a total of 16 subgrade soil samples have been taken atrn1km regular interval and tests were conducted at project geotechnical laboratoryrnfor the determination of Atterberg limit, specific gravity, Natural moisturerncontent, grading, Maximum dry density and Optimum moisture content,rnCalifornia bearing capacity and swell value and hydrometer test is conducted atrnAddis Ababa university Engineering Geological laboratory.rnFinally, interpretation have been made with the data obtained from field worksrnand laboratory investigation, supported by previous studies, research andrnstandard manual of the subgrade characteristics. From the laboratoryrninvestigation it has been concluded that about 37.5 % of the subgrade soil is foundrnto be unsuitable on the bases of bearing capacity. Hence, remedial measures suchrnas removal and replacement, proper drainage design and blending with locallyrnavailable materials are proposed.rnKey words: Subgrade soil, Suitability Analysis, Expansive soil, Volcanic ash

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