Engineering Geological Characterization and Possible Improvements for Sub- Grade Materials, Case Study of Meki-Ziway Highway, Central Ethiopia
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Date
2018-05-02
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Addis Ababa University
Abstract
Engineering Geological Characterization and Possible Improvements for Sub- grade Materials, Case study of Meki-Ziway Highway, central Ethiopia
Hailu Regasa
Addis Ababa University, 2018 .
The present study was conducted to characterize the subgrade of Meki-Ziway High way, which is located in Oromia Regional National State along the main Ethiopian rift system.
Pre-field, field and post field activities including literature, survey primary data and sample collection and laboratory test were conducted to achieve the objectives of this research work. Representative samples of subgrade materials were subjected to laboratory tests for examining their engineering characteristics. Grain size analysis and Atterberg limits tests, proctor test, California bearing ratio and swell tests were conducted for 26 disturbed subgrade soil samples. For other Seven (7) disturbed soil sample, linear shrinkage tests had carried out.
The test results showed that sub-grade soils are classified as CH, CL, MH, ML, SC and SM in Unified soil classification system; A-7-5, A-7-6, A–6, A–5, A–4, A-2-4, A-2-5 and A-2-7 on the American Association of State Highway and Transportation Officials. The test results realize that about 23.19 % of the subgrade sections of the project route have low bearing capacity and due to their low strength, they are not capable of withstanding the stresses, which will imposed on them, unless their quality is improved. Since the subgrade soils along this section is fine grained and too thick, chemical stabilization method was selected for the present research based on the characteristics of sub-grade soil. Accordingly, two (2) disturbed samples were collected and tested for Atterberg limit, proctor test, California bearing ratio and swell by mixing them with Quicklime at different proportion of 2%, 4% and 8%. The improvement of subgrade soil sample increased with increasing ratio of lime as well as curing periods. In general, increased the ratio was more significant affect than that of increased curing periods. It was favorable that 4% of the chemical is suitable to adequate improvement of subgrade soil.
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Sub-grade, Pavement, lime stabilization