Investigation on the engineering properties of soils in fiche town, Ethiopia

Abstract

Fiche is a town in central Ethiopia, located in North Shewa zone of the Oromia Region. The objective of this research is the investigation of the engineering properties of soils found in Fiche town. Disturbed and undisturbed soil samples were collected from Fiche town from ten test pits at 1.5m and 3m depth in order to classify and determine the necessary engineering properties of soils in area. Insitu soil properties show that the natural moisture content for the area under study ranges from 20.01% to 58.89 %. Specific gravity is between 2.62 and 2.88. The specific gravity is above 2.62 indicating that inorganic soils are dominant as most of organic soils contain a value of less than 2.40. The grain size analysis of the area under study shows the soil contains gravel 0-25.62%, sand 1.44%-39.73%, silt 26.29%-55.54% and clay in between 8.67% to 67.51%. This shows that the dominant soil types in the area are silt and clay. The liquid limit of the soils is in the range of 31%-79%. Plastic limit of the soils ranges in between 16% to 42%. Plasticity index for the area under study ranges between 11%-46%. And the free swell result ranges from 35-99%. Soil classification for the area under study is made by both USCS and AASHTO. Soils classification by USCS shows that the soil contains around 41% CH, 18% CL, 18% MH, 14% ML, 4.5% SM and 4.5% SC and AASHTO classification system shows the soils are classified in either of A-6 and A-7. From the compaction test results the maximum dry density (MDD) of Fiche town soil ranges from 1.35g/cm3 to 1.42g/cm3 and the optimum moisture content ranges 28% to 36%. The unconfined compressive strength test of soils has a value of qu between 77kPa to 234 kPa and the amount of cohesion ranges in between 38 kPa to 117 kPa. Consistency is also determined based on the UCS result showing that the soil is medium, stiff or very stiff. Consolidation test was conducted on four different types of soils which are taken based on the classification result. The range of compression index is in between 0.20-0.38 and the preconsolidation pressure values ranges between 85 kPa to 285 kPa. The amount of over consolidation ratio of the soil found in the area under study is determined and it is found between 1.749 to5.45. Since the over consolidation ratio is greater than one, the soil is over consolidated in its natural state. The average values of various tests done at different parts of countries, i.e., Sieve analysis, Liquid Limit, Plastic Index and specific gravities showing different properties. Fiche soils show medium plasticity (clay content) as compared to other towns. The data indicate that there is a considerable similarity of Fiche soils within the physical properties of Addis Ababa and Debre Markos town soils. Some part of the town especially areas at the center of the town i.e around bus station and eastern part of the town is covered dominantly by rock. Thus additional detailed geological study on those areas is highly recommended