Browsing by Author "Natnael, Bekele"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    A Study of Dynamic Properties of Soils Found in Yeka subcity Area of Addis Ababa
    (Addis Ababa University, 2020-01) Natnael, Bekele; Alemayehu, Teferra (PhD)
    Yeka sub-city is located in the North East part of Addis Ababa. The geographical location of Yeka subcity is 9 0 ’ 12 0 latitude N and 38 50’ E longitude. The subcity is characterized by variable topographic features. Addis Ababa is located in seismic zone 3 according to ES EN 2015. The city has moderate seismicity. However, if damage occurs due to moderated seismic activity, its effect might be significant compared to an earthquake occurring on remote areas. Yeka subcity is one of the highly populated areas of Addis Ababa. To reduce future seismic damages, it’s necessary to determine the response of soil deposits in the subcity .Hence the objective of this research is to investigate the dynamic properties of soils found in Yeka subcity. The index properties investigated in this study include; particle size analysis, atterberg limits, free swell and specific gravity. The result of the study showed that, liquid limit ranges from 53 to 85 %, plasticity index ranges between 23 to 45 %, specific gravity values are between 2.61 to 2.71 and free swell ranges 59 to 128 %. . According to Unified Soil Classification System, common soils found in Yeka subcity are classified as elastic silt and plastic clay. In this paper, the shear modulus and damping ratio values of soils commonly found in Yeka subcity was determined using cyclic simple shear test machine on undisturbed samples. The tests were conducted as a function of strain amplitude of 0.01 %, 0.1 %, 1 %, 2.5 % and 5 % under axial stress of 100 kPa, 200 kPa, and 400 kPa. The normalized shear modulus values were determined and the results were compared with curves developed by (Seed and Idriss 1970; Vucetic and Dobry 1991; Dimer 2013; Gemechu 2011; Mengistu 2014).The results reveal that the normalized shear modulus values at lower strains (< 0.01 %) are lower than published literature data. This reduction in values could be due to sample preparation and testing condition. However for higher strains, the computed shear modulus values are within the limits indicated in published literature data.Comparisons were also made with local soils. The shear moduli of the studied soils are fitted well with curves developed for clay soils of Arbaminch and very close to silty soils of Adama. However, the values show slight scatter with silty soils of Ziway. The determined damping ratio values for confining stress of 100 and 200 kPa are within the curve provided by Seed and Idriss (1970) for saturated clays. However, for confining stress of 400 kPa the values are outside the limits.