Browsing by Author "Hailemariam, Trufat (PhD)"
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Item Characterization of Embankment Material with Special Consideration to Clay Core a Case Study for Kalid Dijo Dam in Southern Ethiopia(Addis Ababa University, 2021-09-10) Tafa, Yosef; Hailemariam, Trufat (PhD)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.Item Dispersive Soil Treatment; a Case Study Along Melkasa-Sodere-Nurera-Metahara Road Project, Central Ethiopia(Addis Ababa University, 2020-06-06) Damtew, Fetene; Hailemariam, Trufat (PhD)Portland pozzolana cement (PPC) and Gypsum were used as a stabilizer to treat dispersive subgrade soil along the Melkasa-Sodere-Nurera-Metahara Road project. Experimental laboratory investigation were carried out on two subgrade soil samples to determine the engineering properties of stabilized soils. The untreated soil samples collected from two different locations show a dispersion potential of 69.9 and 99.1 percent, respectively evaluated on a double hydrometer test. Treated soil samples were prepared by varying the amount of cement from 1.0 to 5.5 percent by weight of dry soil sample and gypsum from 2.0 to 8.0 percent by weight of dry soil. The treated samples were evaluated for dispersion potential by double hydrometer test and unconfined compressive strength. The result was evaluated based on the Decker and Sherard dispersive soil classification criteria. The samples treated with cement had shown a huge improvement interms of dispersion potential and satify the non-dispersive soil classification based on the Decker and Sherard criteria at 1 and 2.5 percent for samples A and B respectively. These samples show a higher incement in compresssive strength too. The gypsum treated samples, even if shows a huge improvement in dispersion potenetial, they were failed to satisfy the non-dispersive soil classification based on the crieteria set by Decker and Sherard and it is not considered for treatment of the current subgrade soil. The strength development of soil samples treated with gypsum are lower as compared to cement treated samples.Item GIS-Based Statistical Analysis for Evaluation of Landslide Susceptibility Mapping a Case Study in Blue Nile Gorge Gohatsion-Dejen Road Section Central Ethiopia(Addis Ababa University, 2021-09-06) Ali, Yechale; Hailemariam, Trufat (PhD)The present study was conducted in Blue Nile Gorge Gohatsion - Dejen road section about 185 km from the capital city Addis Ababa. It has been well recorded that the Blue Nile Gorge Gohatsion-Dejen section road corridor was sufferer in different landslides and slope failures. The main objective of the present study was to evaluate landslide susceptibility of the road corridor and produce its landslide susceptibility map. To realize the objectives of this research statistical information value model was basically followed. Seven causative parameters: namely; lithology, elevation, slope, aspect, land use/land cover, proximity to road and proximity to streams were considered for landslide susceptibility evaluation and map preparation. The landslide inventory mapping in the corridor was administered through field observations and Google Earth image interpretations. For statistical information value model the inventory landslide and causative factor maps were converted into the same pixel size raster format then depending on the influence of causative factors on past landslide the information values were calculated. After the statistical information value calculation, distribution of landslide over each causative factor maps was obtained and analyzed. Weights for the class within these causative factor maps were obtained by using statistical information value model. Causative factors are classified into various classes; based on landslide concentration, topographic condition, geology and land cover types in the road corridor/study area. As the statistical information value analysis result; causative factor classes of colluvium deposit, 1575–2100m elevation, > 450 slope, east facing slope aspect, bare land, 0-0.5km distance from road and 0-50m distance from streams have maximum contribution for a landslide occurrence. The landslide susceptibility map, thus produced in the study area clearly indicates that 43.2km2 (17.0%), 96.8km2 (38.1%) and 113.9km2 (44.9%) falls in low, moderate and high susceptible classes respectively. Validation of the prepared susceptibility map revealed that 87.1% of past landslides fall in high susceptible class of the prepared landslide susceptibility map (LSM). Thus, the landslide susceptibility map (LSM) validation provided acceptable results and the different classes those delineated can be safely applied for future developmental planning in the present study area.Item Reliability of Standard Penetration Test to Determine Bearing Capacity of Fine Grained Soil: a Case Study in Addis Ababa Soils(Addis Ababa University, 2017-10-02) Gebremelak, Beza; Hailemariam, Trufat (PhD)Standard penetration test (SPT) is widely practiced in Ethiopia to define fine grained soils’ strength parameter for bearing capacity analysis in foundation design. However, there is no published correlation between the in-situ measured SPT data and soil design parameters to define the reliability of the method. In this research, it is attempted to measure the reliability of bearing capacity estimation from SPT data of fine grained soil using linear regression analysis. SPT data were collected from newly measured SPT data, 22 boreholes in Addis Ababa, with a record of N-value, hammer and anvil type, penetration interval, hammer blow rate, drill rod type, rod length, and drill rig type of to define the bearing capacity of fine grained soil. Besides, corresponding samples were also obtained to determine undrained shear strength and other physical and engineering properties of soil in the laboratory. Initial efforts were made to establish a correction factor of SPT blow N-values to different N-values; N55 N60 and N70. Besides, further correlation and comparison were made between SPT N-values and undrained compressive strength (Cu) considering other parameters such as natural water content (Wn), liquid limit (LL) and plasticity index (PI). Results have shown that SPT N-values are strongly correlated to the undrained compressive strength within the range of limited estimation error. It is also noted that there is mild correlation between two parameters based on the coefficient of regression. The correlation factors are also compared with the previously established coefficients for fine grained soil to show their relevance. As a result, empirical correlation between soil test results and bearing capacity design values are established. Further, correlation values were established between Cu and the in-situ measurement data to define the degree of uncertainty.Item Slope Stability Assessment on A Critical Rock Slope Section Around Alem Ketema, North Shoa, Ethiopia(Addis Ababa University, 2018-05-02) Asmare, Dawit; Hailemariam, Trufat (PhD)Slope Stability Assessment on a Critical Rock Slope Section around Alem Ketema, North Shoa, Ethiopia. Dawit Asmare Manderso Addis Ababa University, 2017 The present research was carried out in an area around Alem ketema town, North Showa, central Ethiopia; with a general objective of conducting a rock slope stability assessment on the selected natural rock slope sections. To achieve this objective, slope stability probability classification and geological strength index approaches were followed to determine the stability probability conditions of slope rock mass in the study area. These classification systems mainly depend on the primary data collected from field works. As a reason, systematic and extensive field work was conducted. However, secondary data was also required in order to characterize the general conditions of the study area and to have a deep understanding on the subject matter. In SSPC system, ratings for degree of weathering, intact rock strength, method of excavation, roughness condition and infill material were given according to standards. The SSPC system uses three step classification systems (exposure rock mass, reference rock mass and slope rock mass). Following these steps, slope rock mass stability probability classifications have been carried out for 92 natural slope sections. The stability of slope rock mass were determined by two different approaches namely orientation dependent and orientation independent stability. Orientation dependent stability related to orientation of the discontinuities and characterized by toppling and sliding criteria, while orientation independent stability related to the strength of slope rock mass. Accordingly, overall assessment indicated that 80.4% of slope sections showed less than 5% stability probability, 10.9% of slope sections showed from 5 to 49%, 6.5% showed from 50 to 95% and the rest 2.2% of slope sections showed greater than 95% stability probability. According to GSI system, the slope rock mass quality obtained falls in to three classes; 63.1% of slope sections showed fair quality, 21.7% showed good quality and 15.2% showed poor quality. All these result were also compared with the visual stability assessment results. Moreover, different stability probability maps were produced for all assessment approaches. Finally, on the basis of findings of the present research, recommendations are forwarded.