Browsing by Author "Geremew, Zemenu (PhD)"

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    Engineering Characteristics of Red Soil: A Case from Western Addis Ababa, Ethiopia
    (Addis Ababa Universty, 2017-06) Akalu, Medhanit; Geremew, Zemenu (PhD)
    The main objective of this research work was to study the engineering characteristics of red soil in the western Addis Ababa.The engineering behavior of residual soils in the area, derived from the in-situ weathering and decomposition of parent rock, is determined by certain physical characteristics designated as engineering properties. For this work both Primary and secondary data from organizations were in use. In this research work, some peculiar geotechnical and physio-chemical characteristics have been investigated on red soils from western Addis Ababa area. Laboratory test results indicate that the reddish brown materials are grouped under silty clayey and clayey soils. The silica to sesquoxide ratio values for two samples of 0.99 and 1.29 indicate that they are true-lateritic soils.The average values of the specific gravity, liquid limit, plasticity index and activity of clay are 2.56, 63%, 18% and 0.37 respectively. They are soils of medium to High plasticity. Free swell result gives an average value of free swell is 52; this indicates medium potential of expansiveness. The direct shear strength test result gives an average value of Cohesion and angle of Friction respectively as 21KN/m2 and 230. Maximum dry density and optimum moisture content values fall between 1.25 to 1.64 g/cm3and 19 to 34% respectively. From the results of UCS average undrained shear strength gives 140Kpa.From Drilled BH data the soil thickness cross section has been produced which clearly shows that the soil thickness in the study area goes up to a maximum depth of 15m.Generally, the soils are classified as A-7-6 to A-7-5 subgroups of the AASHTO classification and according to Unified soil Classification system classify the soil as MH and CL. Finally, based on the general findings of the study, suitable recommendations have been forwarded. Key words: residual soils, physio-chemical characteristics, index tests, mechanical tests and chemical tests.
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    Engineering Geological Characterization and Possible Improvements for Sub- Grade Materials, Case Study of Meki-Ziway Highway, Central Ethiopia
    (Addis Ababa University, 2018-05-02) Regasa, Hailu; Geremew, Zemenu (PhD)
    Engineering Geological Characterization and Possible Improvements for Sub- grade Materials, Case study of Meki-Ziway Highway, central Ethiopia Hailu Regasa Addis Ababa University, 2018 . The present study was conducted to characterize the subgrade of Meki-Ziway High way, which is located in Oromia Regional National State along the main Ethiopian rift system. Pre-field, field and post field activities including literature, survey primary data and sample collection and laboratory test were conducted to achieve the objectives of this research work. Representative samples of subgrade materials were subjected to laboratory tests for examining their engineering characteristics. Grain size analysis and Atterberg limits tests, proctor test, California bearing ratio and swell tests were conducted for 26 disturbed subgrade soil samples. For other Seven (7) disturbed soil sample, linear shrinkage tests had carried out. The test results showed that sub-grade soils are classified as CH, CL, MH, ML, SC and SM in Unified soil classification system; A-7-5, A-7-6, A–6, A–5, A–4, A-2-4, A-2-5 and A-2-7 on the American Association of State Highway and Transportation Officials. The test results realize that about 23.19 % of the subgrade sections of the project route have low bearing capacity and due to their low strength, they are not capable of withstanding the stresses, which will imposed on them, unless their quality is improved. Since the subgrade soils along this section is fine grained and too thick, chemical stabilization method was selected for the present research based on the characteristics of sub-grade soil. Accordingly, two (2) disturbed samples were collected and tested for Atterberg limit, proctor test, California bearing ratio and swell by mixing them with Quicklime at different proportion of 2%, 4% and 8%. The improvement of subgrade soil sample increased with increasing ratio of lime as well as curing periods. In general, increased the ratio was more significant affect than that of increased curing periods. It was favorable that 4% of the chemical is suitable to adequate improvement of subgrade soil.
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    Engineering Geological characterization and suitability analysis of a subgrade soil – A case study on selected section of Ambo – Wolisso Road project, South western Ethiopia
    (Addis Ababa Universty, 2017-05) Mitiku, Biruk; Geremew, Zemenu (PhD)
    The performance of a pavement is highly controlled by the underlying roadbed soil geotechnical characteristics. A subgrade provides support for upper layers of a pavement structure that are constructed upon it and the traffic load. The purpose of geotechnical characterization of a subgrade is to evaluate the quality of the subgrade based on various results of insitu and laboratory test and sound geotechnical principles that would impact the pavement performance. In the present study the subgrade soils are characterized on selected section of Ambo-Wolliso road located in south western Ethiopia, Oromia region. The geographic location of the study area is bounded by UTM coordinate of 80 56’ N 370 52’ E and 8049’ N 37053’ E. the objective of the study were 1, to characterize the subgrade material based on the engineering geological parameters 2, to assess the suitability and bearing capacity of the subgrade soil 3, to suggest some counter measures for the unsuitable part of the subgrade soil. To achieve this objective, a total of 16 subgrade soil samples have been taken at 1km regular interval and tests were conducted at project geotechnical laboratory for the determination of Atterberg limit, specific gravity, Natural moisture content, grading, Maximum dry density and Optimum moisture content, California bearing capacity and swell value and hydrometer test is conducted at Addis Ababa university Engineering Geological laboratory. Finally, interpretation have been made with the data obtained from field works and laboratory investigation, supported by previous studies, research and standard manual of the subgrade characteristics. From the laboratory investigation it has been concluded that about 37.5 % of the subgrade soil is found to be unsuitable on the bases of bearing capacity. Hence, remedial measures such as removal and replacement, proper drainage design and blending with locally available materials are proposed. Key words: Subgrade soil, Suitability Analysis, Expansive soil, Volcanic ash
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    Engineering Geological Characterization of Expansive Soils in Nifassilklafto Sub-City Jemo Area, Addis Ababa, Ethiopia
    (Addis Ababa University, 2021-03-02) Gashaw, Berhane; Geremew, Zemenu (PhD)
    The present study was carried out in Addis Ababa NifasSilikLafto sub city Jemo area with the main objective of characterizing the expansive soils found in Jemo area. Expansive soil in many parts of Addis Ababa poses significant damage light buildings. Therefore, identification, evaluation and characterization of them is a paramount importance to address the problems. In the present study characterization of such expansive soil was adopted by identification and classification based on their laboratory results, correlation of swelling potential and compression indeces with index tests and correlating the laboratory derived and new calculated compression indices values with the well-known skemptons relationship. In order to prepare a geotechnical data base a large quantity of drilling and laboratory testing data, have been filtered out and systematically organized to derive a new relevant correlation for the selected soil type in Microsoft excel. The output of the collected soil sample data is further checked by using five test pits and subsequent soil sampling and laboratory analysis of the most common index laboratory tests according to ASTM standard. From the present study based on the available systematically organized drilling geotechnical data the thickness of expansive soil ranges from 3m to 16m in the study area. The depth profile generally tells that Dark grey silty CLAY/ clayey SILT as a top soil, Light grey silty CLAY/ clayey SILT, Clayey silty SAND having variable thickness. The soils are categorized as CH-clay with high plasticity (fat clay) and MH- CLAY according to the Unified Soil Classification System. Finally based on the correlation between index and swelling pressure no well-defined relationship was found to occur between swelling pressure and index properties. Results of correlations and analysis of compression indices with Liquid Limit and plastic limit show that Cc values generally increases with increasing liquid limit and plasticity index of soils. This serves to suggest that compressibility of soils generally increases with increased plasticity.
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    Landslide Hazard Assessment and Zonation Using Bivariate Statistical Analysis Approach:- the Case Study in Gora Gommany Village and its Surrounding Area in Alaltu District, North Showa Zone, Central Ethiopia
    (Addis Ababa University, 2016-12-04) Beyene, Getahun; Geremew, Zemenu (PhD)
    Landslide Hazard Assessment and Zonation Using Bivariate Statistical Analysis Approach:- The Case Study in Gora Gommany Village and Its Surrounding Area in Alaltu District, North Showa Zone, Central Ethiopia. Getahun Beyene Addis Ababa University, 2016 Landslide is one of the major geo-environmental hazards causing damage to life and property in the Gora Gommany Village. Considering the disastrous effects of the landslides, it is necessary to access the landslides in the present study area. To reduce the damage caused by landslides a Landslide Hazard Zonation map (LHZ) is developed. Landslide Hazard zoning contributes towards sustainable development and planning for mitigation of disaster in the study area. The methodology adopted for the present study was bivariate statistical analysis approach which is based on the past landslides in the area. The Landslide Susceptibility Index (LSI) based on GIS approach and weight evidence modeling (WEM) approaches were followed for preparation of Landslide Hazard Zonation map of the study area. In the present study area 31 past landsides were detected for the analysis of landslide hazard evaluation and Zonation. Six prominent causative factors are considered: Slope material, Slope, Elevation, Landuse landcover, Groundwater and Aspect. For all causative factors the thematic map with scale of 1:50,000 were prepared. The Landslide Susceptibility Index (LSI) was computed for all subclasses of causative factors using Landslide Susceptibility Value (LSV). The calculation of the weight of the parameters was performed to give the weight sum map. For the validation of Landslide Hazard Zonation Map (LHZ) the landslide inventory data was overlaid on LHZ map. The weight sum map was finally classified into five distinctive classes of Landslide Hazard Zonation map. The result obtained shows that Very Low Hazard (16%), Low Hazard (23%), Moderate Hazard 12% , High Hazard 24% and Very High Hazard(25%). The area coverage for Very Low Hazard, Low Hazard, Moderate Hazard, High Hazard and Very High Hazard is 6km2, 9km2, 5km2, 9km2 and 9km2, respectively. The result of validation shows that for weight evidence modeling approach map was less verification than Landslide Susceptibility Index (LSI) based on GIS approach map.
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    Landslide Hazard Zonation Around Ameya Town Konta Special Woreda South Nation Nationality People Region Ethiopia
    (Addis Ababa University, 2021-05-21) Feleke, Awoke; Geremew, Zemenu (PhD)
    In the present study, Landslide Hazard Zonation (LHZ) mapping around Konta special woreda Ameya town is carried out by applying Slope Stability Susceptibility Evaluation Parameter (SSEP) rating scheme. The main objective of the study was to prepare the LHZ map of the study area. A field survey was conducted to map the distribution of existing landslides and the factors that affect the landslide occurrences. Field measurements on structural discontinuities and observation on field manifestations for landslide and related slope instabilities were carried out. For digitizing, data processing, and analysis purposes, A GIS environment was used. In applying the SSEP rating scheme, the relative contribution of each of the intrinsic causative and extrinsic triggering factors were evaluated and ratings were assigned for each factor facet-wise. The intrinsic parameters considered are; slope geometry, slope material, structural discontinuities, land use land cover, and groundwater condition whereas, the external triggering factors are; seismicity, rainfall, and man-made activities. The total of all ratings for causative intrinsic parameters and external triggering factors are represented as Evaluated Landslide Hazard (ELH) established on which the study area is divided into different hazard zones as per the SSEP rating scheme. Then after these the LHZ map of the study area was produced. The prepared LHZ map has identified three zones, namely Very High Hazard (5.12%), High Hazard (66.73%) and Moderate Hazard (28.15%). Finally, the LHZ map was overlaid by past landslide event data out of which 12 % have fallen in the Very High Hazard zone, 72% High Hazard zone the rest 16 % fall in the moderate hazard confirming the validity of the prepared LHZ map. Thus, the satisfactory validation confirms the rationality of considered parameters, the adopted SSEP technique, and the tools and procedures in developing the LHZ map of the study area.
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    Shrink Swell Susceptibility Zonation of Addis Ababa
    (Addis Ababa University, 2020-09-09) Tesfaye, Ijara; Geremew, Zemenu (PhD)
    The present study was carried out in Addis Ababa. The main objective of this study is to carry out shrink swell susceptibility mapping of Addis Ababa. Clay soils are found in many parts of Ethiopia, especially southern, south eastern and south western part of Addis Ababa. Damages due to the shrink swell phenomenon has been frequently reported. Swell potential of such soil can be predicted by both direct and indirect methods. By combining direct and indirect methods of swell potential measurements that predict shrink–swell behavior, a susceptibility map has been established for Addis Ababa. This map shows sensitive areas toward shrink and swell phenomenon. The adopted methodology has been modified from French Bureau of geological and mining research (BRGM) approach. This procedure allowed the identification and spatial variation of shrink swell potential of soil in the study area. Then, they were classified and rated based on their volume changing potential as per given standard. The criterions used to establish susceptibility map are the lithological (plasticity and free swell), geotechnical (clay fraction and thickness of expansive soil) and mineralogical parameters. Each criterion and or parameters was rated, combined and sum together. This summation was divided by the number of the layers (plasticity index, free swell, clay fraction, lithological thickness and percentage of swelling mineral) to get the mean. Finally shrink swell susceptibility map has been produced based on the mean. The formations have been classified in to three classes and represented by tarragon green, yellow and red colors representing low, medium and high susceptibility to shrink swell respectively. The shrink swell susceptibility map shows that 30% (159km2) of the study area has a ‘high shrink swell potential’, 38% (196km2) of the study area has ‘medium’ shrink swell potential. Whereas, the areas that account for ‘low shrink swell potential’ and ‘non clay or rock formations’ are 18% (96km2), 14% (76km2), respectively. Thus, the shrink swell susceptibility map can be used as a regulatory tool in land use and planning procedures.
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    Slope Stability and Sensitivity Analysis Based on Monitoring Data: a Case of Colluvial Slope Failure in the Abay Gorge, Central Ethiopia.
    (Addis Ababa University, 2018-05-04) Manaye, Mihret; Geremew, Zemenu (PhD)
    Evaluation of stability and sensitivity of recurrent landslides involving colluvium materials resting on gentle topographic slope has been carried out along multiple profiles in a landslide zone. The aim is to attempt integrating multiple profile stability analysis into semi- 3D stability model by weighting the factors of safety obtained in the 2D case with the cross-sectional area the above the slip surface of each profile. The 2D and semi- 3D models were implemented in Microsoft Excel spread sheet program using the simplified Janbu‟s method. The selected landslide area is located in the Abay Gorge between the towns of Gohatsion and Dejen, on the northern side of the Gorge. In total, 6 profiles which were aligned approximately parallel to the axis of the landslide from head to toe were evaluated. As the materials are colluvial and deep seated the depth to the slip surface, based on monitoring wells installed in the site, were used to back calculate shear strength parameters using stability charts of Janbu. The back analysis gave residual effective shear strength parameters of (5.7 KPa, 12.60) for profile 8; (5.2 KPa, 11.60) for profile 9; (3.3 KPa, 11.90) for profile 10; (0 KPa, 11.60) for profile 11; (3.6 KPa, 110) for profile 14; (1.7 KPa, 12.20) for profile 15 and (0.3 KPa, 11.80) for profile 16. The Simplified Janbu‟s method of 2D stability analysis at conditions of back analysed shear strength values and the determined water level from site investigation for each profile gave 2D factors of safety as: 1.94, 1.37, 0.84, 1.03, 0.73, 1.06 and 1.08 for profiles: 8, 9, 10, 11, 14, 15 and 16 respectively. The corresponding semi- 3D factors of safety computed by integrating the 2D factors of safety weighted by the respective cross-sectional area was 1.01. The influence on stability was assessed based on the sensitivity of the 2D and semi- 3D factors of safety to the independent changes in value of the shear strength parameters and water level, one at a time. Accordingly three selected profiles in the 2D and all the profiles in the semi- 3D cases showed marked sensitivity to changes in friction angle while the factors of safety had lowest sensitivity to the changes in cohesion. The sensitivity to changes in level of water gave intermediate change in both 2D and semi- 3D factors of safety. The low effect of change in cohesion on the factors of safety might be due to the progressive nature of the landslide. Although simplified and inexpensive methods to analyse the slope stability in semi- 3D approach have been attempted the expected results are not conclusive for various reasons v among which are mixed success with back analysis from slip surface location, and uncertainty in the continuity of the slip surface. Unexpected lower value of the 3D factors of safety might be hence improved by considering solutions to the determination of shear strength parameters and also ascertain continuity of the analysed landslide throughout the model.
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    Stabilizing Expansive Subgrade Soil on a Selected Road Section in Eastern Part of Ethiopia in Somalia Region Jigjiga Tuli
    (Addis Ababa University, 2021-09-18) Negash, Sisay; Geremew, Zemenu (PhD)
    The long-term performance of any construction project depends on the soundness of the underlying soils. Unstable soils can create significant problems for pavements or structures. In order to avoid most of the problems that has been appearing on the upper layer of any pavement it is better to treat the subgrade soil. To achieve the research objectives, subgrade soils samples were collected along the corridor of the road section and evaluated for their physical and geotechnical properties. The laboratory results of previous investigations on the area show that approximately 71 percent of the existing soil has a plastic index (PI) ranging from 27 to 35 percent and a liquid limit (LL) ranging from 55 to 70 percent with an average of 62.5 percent and <5% California bearing ratio (CBR) and approximately 89 percent of the swell values are greater than 2%. This reveals that the sub-grade soil along the route project is primarily characterized by A-7-5 and A-7-6 according to the American Association of State Highway and Transportation Officials (AASHTO) and fat clay (CH) and elastic silt (MH) of UCS soil classification which is considered as a problematic soil for subgrade materials. The swelling pressure of natural subgrade soil was determined using the laboratory to evaluate the fill height of the embankment on the geotechnical properties of soil. Because the swelling pressure of the sub-grade material has a medium swell potential and low potential heave, so soil replacement of only shallow soil not exceeding 30 cm is sufficient (only for the selected stretches) to equalize the swelling pressure of the existing soil with lower swelling potential, higher workability, and stabilized soils were feasible to be used as subgrade materials.