Characterization of Embankment Material with Special Consideration to Clay Core a Case Study for Kalid Dijo Dam in Southern Ethiopia
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Date
2021-09-10
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Addis Ababa University
Abstract
The research is assessing the quality of construction material of the Kalid-Dijo irrigation dam, located in Southern part of Ethiopia, Silte Zone. It is a zoned rockfill embankment dam designed using multi criteria analysis, to tolerable the high probable seismicity that involves quality clay material for its central core. However, the project investigation reveals that the available borrow sites do not fully satisfy the prerequisite for core material. Thus, this research aims to characterize further the locally available clay core material and attempts to forward experiment-based alternatives to meet the required quality for core material of the designed zoned rockfill embankment dam.
The previous studies identified MH core clay materials using USCS near to the dam axis; while in this investigation, the same borrow site classified as CH, to have high compressibility, low dry density, low shear strength, high swell potential and high volumetric shrinkage. It fails to satisfy the general design specification criteria and limits for impervious material.
In this research, blending experiments using different ratios are conducted using the available gravelly material to that of the clay from selected borrow sites. Different tests including classification, proctor compaction, consolidation, free swell, volumetric shrinkage, direct shear, dispersion and permeability tests were conducted on the blended ratios to check the improvement on the clay core material. And it is found out that the required improvement was achieved with 50G:50C mix proportions.
Based on results, the blended GC material (50G/50C) has an average of 1.6 maximum dry density (MDD), 24% optimum water content (OMC), plasticity index (PI) 24, 52.33KPa cohesion (C) and 29.380 friction angle (Ø), which satisfy the basic requirements of core material. It generally showed shows 40% reduction in PI, 12% improvement in MDD, 5% reduction in OMC, and 18% reduction in compression index. It has also a better shear strength and compressibility characteristics than other mix proportions; however, it needs proper care to manage its segregation potential, likely to be resulted from improper mixing in the field that may lead to continuous leakage path within the core during construction stage.
Based on permeability results, all the blended ratios were classed as low to very low permeability (< 10-6 cm/sec). Blended ratio of 40G/80C and 30G/70C is preferable in terms of economy; however, the required engineering properties like compressibility and compaction is relatively low. Therefore, the 50G/50C blended proportion can almost satisfy the standard limits set for design for impervious core material.
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Characterization, Embankment Material, Special Consideration, Clay Core a Case Study, Kalid Dijo Dam, Southern Ethiopia