Integrated Geophysical Characterization for Building Foundation at Kilinto, Akaki Kality Sub-City, Addis Ababa, Central Ethiopia
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Date
2018-06-02
Authors
Getahun, Belete
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Addis Ababa University
Abstract
An integrated geophysical investigation was carried out at a site nearby Addis Ababa Science and Technology University, Kilinto, Akaki, just in front of the Tulu-Dimtu condominiums, Southeastern Addis Ababa, Ethiopia. The principal objective of this research is to map the subsurface geology and elucidate its suitability for the construction of multistory residential and commercial complexes through employing electrical resistivity and seismic refraction techniques. Nine Vertical Electrical Sounding points distributed along five profiles, two dipole-dipole lines and three seismic refraction spreads were conducted to characterize the foundation materials within the study site. Qualitative and quantitative interpretations of the collected data were made by integrating with borehole log data available from nearby areas. The results have revealed that the subsurface geology is consisted of three to four distinct units that reflect different physical properties (resistivity and velocity). The upper most layers consist of black cotton soil (clay and silty clay) have shown very low resistivities (3-11 Ω-m) and low average P-wave velocity (< 350 m/s). The thickness of this layer varies from 3.5 to 7 m. Underlying this unit there is a relatively intermediate resistive (9- 24 Ω-m) and intermediate p-wave velocity (a maximum of 1070 m/s) attributed to decomposed rock with comparatively enhanced thickness. The third and bottom layer associated with weathered and fractured basalt is characterized by relatively high resistivity (25 to 115 Ω-m). The depth to the surface of this unit reaches about 40 m. These properties suggest that the third layer can adequately serve as a competent foundation material that can resist any imposed load from multistory engineering structures. Generally, the study result indicates that the entire study area is characterized by very low resistivity and low compressional wave velocity that is less than 115Ω-m and 1070 m/s respectively. Therefore, development of engineering structures in this vicinity requires proper measures, including proper drainages, compaction, stabilization, removing and backfilling by another well graded material that enable, in order to make the structures stand the impacts of natural geo-hazard event.
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Keywords
Building Foundation, P-Wave Velocity, Resistivity