Investigation On the Engineering Properties of Soil Found in Bishoftu Town

Abstract

This research focused on investigate the engineering properties of soil found inBishoftu town. Engineering properties of soils is useful in understanding theproperties and behavior of soils for the management especially erosion control,farming activities, building, etc. The objectives of this research is to investigatethe engineering properties of soils found in the Bishoftu town by conductingdifferent types of laboratory tests. To achieve its objective disturbed samplesfrom different parts of the town were collected and laboratory tests were doneon the collected samples. The number of test pits taken were limited because ofthat the soil in the entire area of the town is more or less similar. Fromreconnaissance survey it has been observed that the town is covered byexpansive soil. After collecting representative disturbed samples from proposedopen test pits by direct manual excavation, laboratory tests were carried outincluding specific gravity, natural moisture content, Atterberg limit, free swell,sieve analysis, hydrometer tests and direct shear strength test.Grain size analysis tests indicated that, the clay content range from 29.77% to46.38%, silt content range from 54.19% to 63.05%, sand content range from5.08% to 6.72%, and gravel content range from 0.58%to 1.52% therefore the soilin Bishoftu town is mostly silts and caly soil and the specific gravity testsindicated that content range from37.72% to 42.35%.The Atterberg limit test testsindicated that, a liquid limit range from 82%to 90.3%, plastic limit range from29.61% to 38.38% and plastic index from 44.65% to 58.71%. This indicate thatsoil of the study area is highly plastic. The free swell soil test indicated thatfrom127% to 209.5% which indicates that the soil is expansive soil. from thecompaction test result the maximum dry density (MDD) soil ranges from 1.23to 1.46 g/cm3 and the optimum moisture content(OMC) ranges from 38.04 %.Shear strength parameters from the graph of shear stress versus normal stresscohesion(C) ranges from 18.68Kpa to 27.44Kpa and angle of internal friction(??) ranges from 100 to 15.990. Soils of the study area are classified according toUSCS and AASHTO.USCS indicates one main type of soils, which is highlyplastic silt soil (MH). According to AASHTO classification soils of the studyarea is A-7-5.Finally, the pit excavation method of exploration is used, the outcomes wouldbe applicable only for light structures which under lie their foundation up todepth of 2.8m. Therefore, by increasing the depth of the pit excavation additionalinvestigation should be done in the future in order to fully characterize the soilproperties of the area.