Geodesy and Geomatics

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Browsing Geodesy and Geomatics by Author "Alemayehu, Teferra (Prof.)"

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    Ground Response Analysis of Selected Sites in Hawassa Area
    (Addis Ababa University, 2017-11) Besrat, Eshetu; Alemayehu, Teferra (Prof.)
    Hawassa, a lakeside city in southern Ethiopia found at the heart of the East African Rift system, has been frequented with a series of minor to strong earthquakes reaching up to a magnitude of 7. A recent minor earthquake caused structural distresses in the city that tempts one to hypothesize that this may be principally attributed to the young lacustrine deposit typical of the city. Primary data from refraction and resistivity tests and secondary data from available geotechnical reports were collected from different locations of the city so as to model respective soil profiles. Due to lack of measured strong ground motion records in the area, input motions were selected from PEER database using relevant filtering criteria and scaled according to the local seismic hazard. The selected ground motions are used in a one-dimensional ground response analysis software, DEEPSOIL, and responses at the surface and at various depths are obtained. A typical geotechnical profile across the city consists of a thick silty sand soil with a thin horizon of welded-tuff at a shallow depth. The results obtained from the study show that ground motions are greatly influenced by local site soils across the selected locations, with amplifications much exceeding the prediction of design spectra specified by current codes. This led to the proposal of a design spectrum that fitted the analysis outputs from 56 cases.
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    Software Development for Consolidation and Settlement Analysis
    (Addis Ababa University, 2011-11) Ayenew, Yihune; Alemayehu, Teferra (Prof.)
    Consolidation and settlement analysis is one of the main tasks of a geotechnical engineer. There are different methods of analyzing consolidation and settlement. In this study, software for the analysis of consolidation and settlement is developed. The developed software analyzes one dimensional consolidation for saturated and unsaturated soils. Consolidation analysis for saturated soils is done by the Fourier series solution and by finite difference solution of Terzaghi’s one dimensional consolidation equation for saturated soils. Consolidation analysis for unsaturated soils is done by finite difference method. The analysis is done for different loadings, scenarios, drainage conditions and soil conditions. The software analyzes immediate settlement, primary settlement and secondary settlement. Primary settlement calculation is done by compression index method, average modulus of compressibility method and coefficient of volume compressibility method. Secondary settlement calculation is done by constant modulus of compressibility method and variable modulus of compressibility method. The analysis is done for different loadings, foundation types, and locations of the foundation, drainage conditions and soil conditions. The result of consolidation analysis by Fourier series method and finite difference method give approximately similar result. For the consolidation analysis by finite difference method, the stability of the calculation is very sensitive to the beta value. The result may not be reliable for inappropriate beta values. The developed software can be used to analyze consolidation and settlement simply, quickly and accurately. Comparison of results obtained from different analysis methods of consolidation and settlement can be also made with the software. The developed software is also important to study the properties of the results for different values of input parameters.