Engineering Geological Characterization and Suitability Analysis of Subgrade Materials -a Case Study of Sembo-Shola Gebeya-Gindeber Road, Central Ethiopia
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Date
2014-05-05
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Addis Ababa University
Abstract
Characterization of Subgrade soils is one of important parameters in the design and construction of long life pavement structures. Thus the characterization involves identification of problematic soils to design accordingly and to take counter measures. The most common problematic soils in flexible pavement construction are expansive soils that change in volume under moisture content and ground water fluctuation, that cause severe damages to infrastructure unless proper measures are taken in the design and construction phases.
The subgrade soils are characterized in Sembo-Sholagebeya-Gindeber upgrading project located in Northern Shoa connecting Kimbibit and Hagremariam woreda bounded by UTM coordinates of 538556E, 1040338N and 544927E, 1018404 N that ranges from 2600m to 3000m above sea level and geologically covered by volcanic rocks of mostly basaltic. The main objective of this study were: (1) to characterize the engineering properties of the subgrade soils, (2) to identify the problematic soil and analyze its suitability for pavement, (3) to propose a remedial measure and (4) to propose alternative pavement thickness.
To achieve these objectives, the pre-field, field and post field activities including literature survey, primary data, sample collection and laboratory works were conducted during the study. Accordingly 82 samples have been collected at an interval of 500m and tests are conducted at project geotechnical laboratory for the determination of Atterberg limits, grading, MDD and OMC, CBR and CBR swell values. In addition 5 samples are chemically analyzed using XRD, 2 rock samples for thin section and 2 samples for triaxial.
Finally interpretations have been made with the data obtained from field works and laboratory investigations, supported by previous studies, researches and standard manuals of subgrade characterization. From the laboratory investigation, it has been concluded that about 41% on plasticity, 62% on CBR, 64% on CBR swelling, 46% on Group index of the sub grade soils are found to be unsuitable and all are highly compressible. Hence remedial measures such removal, mechanical compaction, proper drainage, chemical treatment, blending with existing soils and proper pavement thickness design are proposed in this paper.
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Subgrade, Suitability, Characterization, Pavement, Engineering Properties