School of Civil and Environmental Engineering

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Browsing School of Civil and Environmental Engineering by Author "Abate, Negede (PhD)"

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    Design and Analysis of a High Dam under Construction Material Constraint Condition (Case Study: Wolkayite High Dam
    (Addis Ababa University, 2014-06) Mekuria, Bahru; Abate, Negede (PhD)
    In many countries, dams are currently under construction and to due constructed to impound water for different purposes such as flood control, water supply, irrigation, energy generation, and recreation as well as pollution control. Nowadays utilization of selected materials for making the dam body is vital and very common. In cases of high embankment dam projects, which require large volume construction material, availability and adequacy of selected material to the allotted quantity is crucial. Wolkayite high embankment dam project suffers by the presence of highly plastic clay and highly weathered shell material for the construction of its dam body. There is also abundant rockfill material, but require high processing to use resulting high project cost. In this paper, the author sought alternative material for the design and analysis of the dam by assessing different construction materials located within the economic distance of the project site satisfying different design standards in the area with comparable cost. As the dam is above 90% full throughout its design life, the u/s side of the dam was designed as free draining rockfill whereas the d/s side was designed as random fill surrounded by alluvial river gravel fill and rockfill materials. Using recommended design standards: basically USBR, USACE and other recommendations the design and analysis of Wolkayite High Dam was conducted using Geo-studio 2004 and PLAXIS 8.5 software products. Finally, the proposed material type was checked for different design criteria as fill materials making the dam body. Since the results gained after the analyses were in the recommended range, the author recommends this alternative design solution for the Wolkayite high dam project. KEYWORDS: Design of embankment dams, Material selection, Wolkayite Dam, seepage, settlement, stability analysis.
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    Design and Analysis of Headwork on A Challenging Foundation Condition (The Case of Kuraz Project on Omo River)
    (Addis Ababa University, 2014-06) Negash, Fekremariam; Abate, Negede (PhD)
    The foundation geology at a diversion site often dictates the type of dam suitable for that site. The strength, thickness, and inclination of strata; permeability; fracturing; and faulting are all important considerations in selecting the diversion structure type. Occasionally, like the problems in Kuraz project the foundation formation show clear distinction in vertical level of appearance of a given material, two clear distinct faults within its longitudinal span axis, the structure‟s immediate foundation is resting on alternating strong and weak formations with different bearing capacity exerting differential pressure creating overstress in the structure will create differential settlement and the existence of the sandy silt formation at different levels along the longitudinal axis creates a liquefaction prone soil during an Earth quake. The major objective of this project is to study the Design and analysis of a diversion head work or small dam on a challenging foundation condition especially solving the problem on Kuraz Project on Omo River by providing technically, economically and functionally plausible alternative solutions. In this research the following have been accomplished: important data were collected from existing documents, laboratory test results and other secondary data sources of the project and the final computation and the analysis is presented using Geo-Studio soft wares. Thus, the scope of the research will be limited to identifying or selection of appropriate headwork typology, hydraulic design and analysis of a foundation for the structures on the existing complex geology requiring very careful approach. In additions the research emphasizes to demonstrate theories, procedures and techniques through practical applications. For this particular challenging foundation conditions, it was proposed three different possible alternatives. which wereOn the rock foundation (right side) concrete weir and on the island and left side of the structure earth fill Dam, on the rock foundation (right side) concrete structure and on the island and left side of the structure earth-rock fill structure and Entire weir structure which is proposed by WWDSE.Hence after design of all the three alternatives of the structures and analysis using Geo-Studio software the results indicate that for the embankment part of the structures, the first alternative was selected as the most economical, functional and practical plausible alternative.
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    Upgrading and Rehablitation of An Existing Water Supply Schem The Case of “Midmar Embankment Dam “
    (Addis Ababa University, 2011) Tesfay, Berhanu; Abate, Negede (PhD)
    Midmar dam was designed as water supply source project for Adwa, small town named Adi-Abun (Currently merged with Adwa town) and for Almeda Textile Factory. However, recently, the dam is also serving as water supply source for Axum town which was not considered during designing phase, Hence, the main objective of this paper is to evaluate the existing and suggest possible remedial engineering measures so as to harvest maximum water as much as possible in a hydrologic year as well as comparing the harvested water with future water demands. SEEP/W software model is used to analysis quantity of seepage through dam body and foundation at both scenarios (At existing condition and with design modification), when compared with the quantity of seepage estimated at the design document, the designed documents has no problem. SLOPE/W model is used to computed slope stabilities at different scenarios under different loading conditions as per the analysis results at the existing condition the dam is more stable and the result of SLOPE/W for modified ( after dam height increment by 2m ) shows that the dam is still safe and stable. As per water demands for Adwa and Axum towns at the existing condition Midmar dam can serve up 2023 G.C safely and when modified as a result 2.5 MCM volume of water can be stored additionally, that is more than 33 % increment in water holding capacity of the dam has been achieved and therefore the dam can serve as water supply source up to 2033G.C safely. Design modification for existing spill way is not found as such satisfactory as upgrading option as per the second upgrading option additional 22.39ha can be inundated, therefore social, environmental and compensation issues should have to be kept in mind.