Integrated Geophysical and Geotechnical Investigations for the Building Site Characterization of Wolkite University, Gubre, Wolkite, Ethiopia.

Alemayehu, Ayele (2012) Integrated Geophysical and Geotechnical Investigations for the Building Site Characterization of Wolkite University, Gubre, Wolkite, Ethiopia. Masters thesis, Addis Ababa University.

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A foundation study has been undertaken at the site of the newly proposed Wolkite University Campus. The site is located northeast of Wolkite town in southern-western Ethiopia, about 170km from Addis Ababa city at the place called Gubre. The current study is aimed at evaluating the competence of the near surface formations as foundation materials. Integrated geophysical and geotechnical methods have been used. For the geophysical investigations, 2D Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES) and magnetic surveys have been employed. For the geotechnical investigations, the foundation soils are characterized and classified based on their visual interpretation and different laboratory tests. For the geophysical investigations four profiles- three of which run east west and are nearly parallel to each other and a fourth perpendicular profile- of ERT and 3 VES on Profile-2 are conducted to know the different electrical properties of sub-surface conditions at the proposed building site. The ERT and VES results show the presence of intermediate resistivity top soil, an even lower resistivity second layer of clay and/or high moisture content, weathered and fresh bedrocks, and the presence of weak zones in the site. Furthermore, the sliced- stacked apparent resistivity pseudosection map presents electrical resistivity variation of the subsurface that shows both the lateral and vertical variations in lithology of the subsurface. In addition to these, the magnetic anomaly map depicts the zones which show high and low magnetic anomaly response that resulted from variations in lithology and their depth. Furthermore, analytical signal map and tilt derivative of analytical signal map that were produced from the magnetic data show magnetic anomaly contrast over the weak zones in the survey area. Finally, Euler depth map and 2D magnetic modelling are used to know the depth of the magnetic sources that are associated with the structures. The correlation of the magnetic anomaly plot and 2D inverse model resistivity sections are used for the identification of weak zones that need special design in the site. During the current study, soil samples from 20 test pits were tested for Atterberg limits and swelling potential. From amongst the twenty, samples from nineteen tests pits were tested for specific gravity, natural moisture content and grain size distribution. All the soil samples from the study area fall into intermediate to high plasticity silt and intermediate clay soils, except for three samples which shows very high plasticity silt soils. Intermediate to high plasticity soils of the study area shows fair to poor engineering property but very high plasticity silt show very poor engineering property. In general, the soils of the study area may be classified as 35% CL, 50% ML and 15% MH. Therefore, According to general engineering suitability chart, 85% fair bearing capacity and remaining 15 % reveal poor bearing capacity. The geotechnical results show that the subsurface foundation material (soil) in the site is good to fair bearing capacity. This is relatively suitable for low rise buildings. The geophysical results reveal potentially hazardous sub-surface zones that show unfavourable subsurface conditions to multi-storey buildings. These zones are clearly mapped so that it is possible to preferentially select the building foundation sites away from these weak zones. Finally, since the study area is situated in seismically active zone, and as a result of this, designers should consider the seismic code in addition to the building code before designing of the multi-story buildings and other heavy infrastructures over the site.

Item Type: Thesis (Masters)
Subjects: Q Science > QE Geology
T Technology > T Technology (General)
Divisions: Africana
Depositing User: Selom Ghislain
Date Deposited: 19 Jun 2018 13:47
Last Modified: 19 Jun 2018 13:47

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