Browsing by Author "Samuel, Tadesse (PhD)"

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    Developing Correlation Between DCP And CBR For Locally Used Subgrade Materials
    (Addis Ababa University, 2012-06) Yitagesu, Desalegn; Samuel, Tadesse (PhD)
    California Bearing Ratio (CBR) is a commonly used indirect method to assess the sub grade soil strength in pavement design works. However, since CBR cannot be easily determined in the field, civil engineers always encounter difficulties in obtaining representative CBR values for design of pavement. Consequently, prediction of CBR va1ues from other direct soil field tests such as Dynamic Cone Penetrometer (DCP) is found to be a valuable alternative. The dynamic cone Penetrometer (DCP) is the most versatile rapid, in situ evaluation device currently available. Its correlations to CBR and its use in performance evaluation of pavement layers make it an attractive alternative to more expensive and time consuming procedures. Many useful correlations had been proposed by various researchers for soils of their locality in which the DCP penetration index was used to develop these correlations. A study was carried out to find the correlation between Cone Penetrometer (DCP) with CBR values that best suit the type of soils in Ethiopia. Accordingly, several laboratory tests and field tests on Jimma – Mizan, Contract 1: Jimma – Bonga road project from km 100+000 to km 105+000 has been conducted. From the tests, the Atterberg limits (PI, LL, PL), In situ density, classification (sieve analysis, hydrometer analysis), California bearing ratio, insitu Moisture Content, and Dynamic cone penetration results are acquired. Based on this laboratory and field test results analyses were carried out using SPSS software and the applicability of the existing correlations for Ethiopia soil on the aforesaid data was checked. From the analysis results, it is observed that the published correlations are not suitable to be used in Ethiopia. Consequently, a correlation had been proposed in the study to predict the CBR values of the sub grade soil from dynamic cone penetration test results. The relation obtained from statistical analysis relationship has an R 2 of 0.943 and is shown below. log (CBR) = 2.954 – 1.496log (DCPI) with R 2 = 0.943 The results of the statistical analysis show that good correlation does exist between the dynamic cone penetration indexes (DCPI) and unsoaked CBR values.
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    Effect of Strain Rate on Undrained Shear Strength and Sensitivity of Red Clay Soil Found in Addis Ababa
    (AAU, 2018-03) Rabia, Hussen; Samuel, Tadesse (PhD)
    Soil presents itself to be one of the most complicated materials owing to widespread variation of its properties which changes in both geometrical composition and time based contexts. For design and analysis of any structure supported by soil, the shear strength parameters of the soil are vital and they should be obtained from laboratory and in-situ tests. Since the shear strength parameters are not intrinsic properties of soil, there are a number of factors which affect the estimates obtained from tests, out of which rate of loading or shearing and the initial degree of compaction poses to be the most important factors that should be taken in to account while conducting the tests. In Addis Ababa lot of construction activities are seen like foundation structure of heavy duty machineries, high rise building, slope stability in embankment fill, design of highway pavements and deep vertical excavation. In doing such activities the strength and properties of soil which the structures to be built must be studied. The shear strength of the soil is affected by the rate of strain. So it is necessary to incorporate the effect of varying strain rate on such geotechnical problems. In this study, the effect of strain rate on undrained shear strength of both undisturbed and remolded samples and sensitivity of red clay soil are investigated using unconfined compression tests. In this thesis, the UC tests were carried out on undisturbed and remolded samples using different strain rates which are obtained from the coefficient of consolidation for each load increment of one-dimensional consolidation. The strain rates are (0.37, 0.84, 1.03, 1.12, 1.61, 1.75) and (0.23, 0.53, 0.61, 0.68, 1.06, 1.14) for the undisturbed and remolded samples respectively. The remolded samples are tested for both strain rates in order to determine sensitivity accordingly. The undrained shear strength increases from (62.7 to 256.5) kPa and from (59.6 to 157.5) kPa as the strain rate increases from (0.37 to 1.75) mm/min for undisturbed and remolded samples respectively and also from (45.3 to 123.9) kPa as the strain rate increases from (0.23 to 1.14) mm/min for the remolded samples. The failure strain decreases from (8.95 to 3.29) % and from (15 to 7.24) % as the strain rate increases from (0.37- 1.75) mm/min for undisturbed and remolded samples respectively and also from (15 to 9.21) % as the strain rate increases from (0.23 to 1.14) mm/min for the remolded samples. The sensitivity increases from (1.05 to 1.63) and (1.38 to 2.07) as the strain rate increases from (0.37 to 1.75) and (0.23 to 1.14) respectively. The test results show that, as the strain rate increases the undrained shear strength increases and the failure strain slightly decreases for both undisturbed and remolded samples and also the sensitivity increases. Besides on the basis of their sensitivity, the soil in the study area can be classified as insensitive.
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    Exhaustive Literature Review Dealing with the Relationship between CBR, Ks, and Resilient Modulus
    (Addis Ababa University, 2015-11) Fekadu, Eshetu; Samuel, Tadesse (PhD)
    In high way formation the sub grade layer, where acts as a pavement foundation should be well designed. In order to provide a suitable design input for identifying the bearing capacity and stiffness/strength of sub grade materials, it is very important to conduct laboratory and field tests like CBR, MR and Ks. However, in the current practice it is too difficult to carry out cyclic tri axial tests for determining resilient modulus and filed plate load test for modulus of sub grade reaction, due to the unavailability of the testing apparatus widely, time consuming conducting the test and requires very high cost performing the test. This paper presents an exhaustive literature review to evaluate the suitability and reliability of different correlation equations used to calculating MR and Ks, so far developed by many writers on the relationship of CBR, MR and Ks. The work has begins with referring different papers and selecting the correlation equations studied for different type of soil natures. Then with a known CBR value calculating the value of MR and Ks for all equations on the table and plotting them on the graph. After plotting all equations on the graph, explain the behaviour and the similarity between the equations and identify which equations are better useful for predicting the values of MR and Ks. From this literature review one can have the information of how to predict the values of modulus of sub grade reaction and resilient modulus from the correlation equations without performing filed plate load test and cyclic tri axil laboratory tests.
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    Identifying and Optimizing Suitable Source of Ballast Material (Case Study on Sebeta-Meiso-Dewalle Railway Project)
    (Addis Ababa University, 2015-08) Biruk, Gebremedhin; Samuel, Tadesse (PhD)
    Previously great attention has been given for the quality of track superstructure to improve the general technology of the railway scheme. But frequent research on track supporting materials show a good result which improves the general overall performance; safe ride with smooth wheel-rail steering ,high speed, minimum initial cost and accepted tolerance with respect to voice, and vibration .Generally positive whole life cycle analysis are the basic concern on the railway technology. And such a good quality in strength and life cycle of railway track component contribute high for the performance of the general track structure in different angles. In Ethiopia, on the new projects of railway; ballast as a basic constitute and determinant part of the selected ballistic electrified track; many researches not yet done in maximizing its efficiency on the coming project. And General selection of uneconomical quarry sites which is not located on the logical acceptable radius of the project , stated as the core problem of the thesis and their respected cost variation they experienced on the project studied in depth. In order to elaborate it , case study is selected on recently undergoing Ethio -Djibouti railway project of section Sebeta - Meiso ; two uneconomical quarry sites (Adama-Awash) selected by the contractor which are located out of the logical economic radius pointed down. The aim of this thesis is to access and study many different aspects which affect the general selection of the ballast materials; exploring additional quarry site in between Adama and Awash quarry sites and came with solution with minor blending with neighboring quarry to meet the required standard engineering properties. Finally this thesis finds alternative and reasonable solution of quarry configuration (Adama- Arole-Awash) after detailed economic evaluation and acceptable laboratorial results which experience high cost minimization than currently selected quarry site configuration (Adama- Awash) by the contractor.
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    Improving Engineering Properties of Expansive Soils of Addis Ababa by Blending with Pozzolanic Sand Found around Meki Town
    (Addis Ababa University, 2020-12) Wolde, Ketema; Samuel, Tadesse (PhD)
    Black Cotton Soils exhibit high swelling and shrinking when exposed to changes in moisture content and are most troublesome soils leading to failure of civil engineering structures constructed on such soils. The purpose of this study is to investigate the effect of pozzolanic sand on improving the engineering properties of expansive soil collected from Addis Ababa around Koyefeche condominium site. In this research, pozzolanic sand found around Meki Town was used to treat problematic expansive soil. The pozzolanic sand used for treating the expansive soil was pulverized to pass certain sieve sizes. In this particular research, to consider the size effect of pozzolanic sand on treating the expansive soil, pozzolanic sand passing 150μm and 75μm sieve size were used to treat the expansive soil. The pozzolanic sand crushed to a size less than 150μm was blended to the soil up to 25% at 5% percentage increments whereas the pozzolanic sand crushed to a size less than 75μm was blended with soil to a maximum of 15% at 2.5% percentage increments by dry weight of the soil. Soil treated with the pozzolanic sand showed improvements to plasticity, strength and swelling. As soil is treated with pozzolanic sand the plasticity of the soil decreased, the dry density of the soil increased, the optimum moisture content decreased and the swelling pressure also decreased. Besides, the compressive strength of the soil increased as the percentage of pozzolanic sand is increasing. For the sizes of pozzolanic sand considered the pozzolanic sand crushed to a size less than 75μm improved the engineering properties of expansive soil than the pozzolanic sand crushed to a size less than 150μm when blended with the expansive soil.
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    Improving the Strength Characteristics of Red Clay Soil Using Waste Plastic Strips
    (Addis Ababa University, 2020-06) Eleni, Abebaw; Samuel, Tadesse (PhD)
    Soil stabilization is the physical and chemical alteration of soils to enhance their physical properties. Stabilization can increase the shear strength of a soil and control the shrink-swell properties of a soil, thus improving the load-bearing capacity of a sub-grade to support pavements and foundations. Stabilization can be used to treat a wide range of sub-grade materials from expansive clays to granular materials. The cost of introducing traditionally available stabilizers has increased in recent years which opened the door widely for the development of other kinds of soil stabilizers such as plastics, bamboo etc. The research is basically conducted by waste plastic strip and red clay soil found in KecheneRas Desta road. The significance of the study is to provide alternative stabilization material in construction industry. The objective of this study is to improve the strength characteristics of soil using the stabilization of plastic strips. In this regard an attempt has been made to evaluate the effect of plastic strip as a stabilizer on the geotechnical properties of red clay soil in stabilized form mainly strength and compaction characteristics. The preliminary investigation of the soil to be stabilized shows that it belongs to A-7-5 class of soil in the AASHTO soil classification system. Soils under this class are generally of poor engineering use. Therefore, series of laboratory tests such as Atterberg limits, free swell index, compaction, UCS and soaked and unsoaked CBR tests for different percentages of plastic were performed. The soil was stabilized with plastic in stepped concentration of 0%, 0.5%, 1.5%, 2.5%, 3.5%, 5%, and 7.5% by dry weight of the soil. The analysis shows slight improvement on the geotechnical properties of plastic stabilized soil. The plastic strip is found to increase the unconfined compressive strength of the soil up to 5% of plastic (75.01 kPa to 196.14 kPa) and CBR result of the red clay soil up to 2.5% (soaked CBR from 3.5% to 5% and unsoaked CBR from 80.3% to 108.7%). Due to plastic’s light weight property the MDD of the soil shows slight increase up to 2.5% of plastic from 1.4g/cm3 to 1.53 g/cm3, and as the ratio of the plastic increased in the clay soil the result decreases.
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    Index and Mechanical Properties of Collapsible Soils (A Case Study on Ziway-Arsi Negele Highway Project)
    (Addis Ababa University, 2019-12) Tewodros, Dugasa; Samuel, Tadesse (PhD)
    Collapsible Soils, unlike many other types of problematic soils found in Ethiopia, did not get the necessary attention in researches conducted to this date. However, due to their particular engineering characteristics, they exhibit large settlement upon wetting posing threat to embankments and foundations built over them. Due to lack of researches on collapsible soils and the limited attention given in engineering design manuals of the country, many professionals in the construction industry fails to clearly understand their index and mechanical properties. This research had the aim of assessing the index and mechanical properties of collapsible soils found between Zeway and Arsi Negele towns by taking the ModjoHawassa Dual Carriageway Highway Project, Lot 3; Zeway-Arsi Negele as a case study. To this regard, a series of field and laboratory tests were conducted on representative collapsible soil samples collected from the above-mentioned study area. Field density test has been conducted to determine the in-situ densities of the sampling areas. Furthermore, laboratory tests like specific gravity, grading analysis, Atterberg limits, and moisture-density relationships have been carried out to determine their index as well as mechanical properties. In so doing, it was observed that the soils have very low in-situ densities, mainly consist of sands and silts and low plasticity. Moreover, in order to investigate the collapse nature of the soil samples, collapse potential test has been carried out using one dimensional Oedometer by remolding the samples to their in-situ as well as maximum dry densities so as to perceive the nature of collapsibility of the soils at their natural state and at their compacted state. Accordingly, it was found out that the soils have moderate collapse potential at their natural state and does not exhibit any kind of collapsibility at their compacted state.
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    Investigation of Index Properties and Swelling Potential of Expansive Soils in Lege Tafo Area
    (Addis Ababa University, 2019-05) Saba, Mesfin; Samuel, Tadesse (PhD)
    This Study is conducted on Lege Tafo area which is located on flat plain just east of Addis Ababa City. The area is covered with thick clay soil and new infrastructures are under construction in the region as part of the fast growing urbanization and industrial development around Addis Ababa and this is one of the reasons why the area is selected for the study. The objective of this research is to understand the nature of the soil and obtain sufficient information on type and characteristics of the soil in the area to provide general data for future construction projects. To achieve these objectives the surrounding of Lege Tafo is studied in the field, and representative clay soil samples are collected and analyzed in the laboratory. Black soils in Ethiopian are derived from weathering of basalt volcanic rocks and are invariably clays or silty clays. Natural deposits of black cotton soils in the field are characterized by a general pattern of surface cracks during the dry season of the year. During wet seasons, the soil first expands horizontally, filling up the shrinkage cracks. Further volumetric expansion causes vertical heaving of the soil which may cause damage to an overlying structure. Deformations occurring in the soil affect the stability of structure negatively, and the consequence could be tremendous loss. A total of 15 disturbed and undisturbed soil samples were collected from 9 test pits. Three undisturbed samples at 2 meter depth are tested for investigation of swelling pressure. Expansive soils of Lege Tafo are generally black in color and underlain by gray soils that have significant swelling potential. From soil classifications, soil samples taken from 2 meter and 3 meter depths have shown the same capacity for expansion/ swelling potential. As a result of this swell consolidation test was conducted on three samples collected at 3 meter. The soil in the study area is mostly clay ranging from 53.6-75.3%, silt 22.9-33.6%. According to consistency test results, liquid limit ranges from 91 -116%, plastic limit from 27.8-46.6% and plastic index from 52.37-81.6%.Within the depth of investigation, the specific gravity of the study area ranges from 2.60 to 2.85. According to the Unified Soil Classification System, the soil in the study area is categorized as highly plastic inorganic clays. AASHTO classification system also shows that the soil is highly plastic with a potential for a considerable volume change. Swelling pressure test carried out on undisturbed samples from the study yield results ranging from 76 kPa to 165 kPa. The results are compared with results of previous studies on similar soils around Addis Ababa.
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    Potential Use of Rice Husk Ash as Woreta Expansive Soil Stabilizer
    (Addis Ababa University, 2020-12) Chalachew, Admas; Samuel, Tadesse (PhD)
    Expansive soils cause serious problem in the civil engineering practice due to swell and shrinkage upon wetting and drying. In Woreta this soil is the dominant and extends to very deep depth. In this study, the potential use and the effectiveness of expansive soils stabilization using rice husk ash are evaluated. Rice husk ash is the most locally available agricultural waste material in Woreta and it is an attractive pozzolanic. According to the chemical content test the main component of the rice husk ash is silica and its amount is about 76%, which is the element that governs the reactivity of the ash. The effectiveness of this ash in soil stabilization is tested in the laboratory by conducting laboratory tests like compaction, California bearing ratio, unconfined compressive strength, Atterberg limit, specific gravity, and free swell on uncured and 7 days cured samples with a different percentage of ash (5%, 10%, 15% and 20% of soil dry weight) with and without the amendment of 4% lime. The results obtained, indicates that the use of rice husk ash in soil stabilization generally increase strength and decrease swelling potentials. The liquid limit, plasticity index, maximum dry density, specific gravity, and free Swell properties had been decreased with the addition of rice husk ash, while the OMC increased. The UCS test results indicated that the treated soil increases by 23% and 67% for uncured and by 49% and 119% for 7 days cured sample in strength over that of the virgin soil with the addition of 5% and 10% rice husk ash respectively. Also, the combination of rice husk ash with 4% lime enormously increase the UCS value for both cured and uncured samples. Others parameters found to be improved are the CBR value and it increased from 1.2% to a maximum of 2% for uncured and 2.4% for 7 days cured with the addition of 10% rice husk ash alone and around 17% for uncured and 22% for 7 days cured with the addition of 10% rice husk ash amended with 4% lime. Nonetheless, both the UCS and CBR of treated expansive soil reduced slightly when the rice husk ash content was greater than 10%, which indicates that the optimum amount to achieve the highest strength is around 10% rice husk ash content. Both UCS and CBR values increase significantly due to the presence of curing.
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    Prediction of Soaked CBR value From Index Properties and Compaction Characteristic of Subgrade Soils
    (Addis Ababa University, 2019-10) Dereje, Bogale; Samuel, Tadesse (PhD)
    The subgrade provides the foundation for the pavement material and should be well compacted to utilize its full strength. The subgrade strength is related to the CBR value of soil. The CBR test is laborious and time consuming and must always be performed on remolded soil samples. The CBR values depend on the type of soil as well as other soil properties. Hence, it is important to develop correlations between CBR and index properties for the subgrade soils. In this research work, an attempt has been made to establish a correlation of CBR values as function of different index properties and compaction characteristics of soil specific to JinkaMendir design and build road project subgrade soils. In order to achieve the intended correlations, a series of laboratory tests have been conducted on forty one soil samples. Based on the laboratory test results, the collected soil samples are categorized into two groups, namely coarse-grained and fine-grained soils. Accordingly, twenty five of the soil samples are classified as coarse-grained soils and the remaining sixteen soil samples are classified as fine-grained soils. This research work was done on twenty three coarse-grained soils and fourteen fine-grained soils with two control tests for both of the coarse-grained and fine-grained soils. For this research work, statistical software (SPSS) was employed to investigate the significance of individual independent variables. Using multiple linear regression analyses, good correlations were obtained between soaked CBR and index properties test results for coarse-grained and fine-grained soils with coefficient of determinations of 0.866 and 0.931 respectively. After validating the developed correlation with control test results, it was noted that the correlations of CBR values with soil index properties are more applicable for preliminary characterizing of the strength of subgrade soils.
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    Relationships between Plastic Index with Linear, Volumetric Shrinkage for Tendaho Road Project
    (Addis Ababa University, 2019-03) Tesfaye, Mebratu; Samuel, Tadesse (PhD)
    Currently there is a belief within the geotechnical Engineering Profession that there is not strong form of correlation between plastic index with linear, volumetric shrinkages properties for a soil [16]. This project would concentrate on soils from one particular road project which is known as tendaho access road. The soils in tendaho have been predominately consist of clays, silts, sands and gravels. The analysis to determine if there is a relationship between plastic index with volumetric shrinkage, plastic index with linear shrinkage results was undertaken using a sampling and testing program for 29 soils that had different characteristics. The soils that were tested all originated from Pliocene-Pleistocene volcanic rocks and associated fluvio-lacustrinesediments. this formation and are located in in Afar depression 580 kms North-East of the capital Addis Ababa, within the lower delta of Awash basin. The soils that were tested ranged from silts with sands and extended through to moderatly reactive clays. All these samples were subjected to the same testing program and included atterberg limits, linear shrinkage, volumetric shrinkage, free swell and particle size distribution. Upon completion of the testing program the volumetric and linear shrinkage results were plotted against the plastic index. This data was then graphed and the strongest trendline was fitted to it and the corresponding equation calculated. For a correlation to be considered a useful estimating tool the strength of this relationship must exceed R2 =0.80[14]. There were three correlations which met the requirement of R2 > 0.8.The equations for these correlations could be used to estimate the plastic index from linear, volumetric shrinkage of a soil.
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    Simple Model for Wall Deflection Caused by Braced Excavation in Clays
    (Addis Ababa University, 2020-10) Firehun, Matebo; Samuel, Tadesse (PhD)
    Due to space limitations in urban areas, underground construction has become a common practice worldwide. When using deep excavations, excessive lateral movements of wall and adjacent structure are a major concern because they can lead to significant displacements in adjacent structures. Therefore, an accurate predictions of lateral wall deflections were a major concern for design and construction of excavation support system. The objective of this thesis is to develop a simple polynomial regression model for predicting maximum wall deflection due to deep excavation, in clays. The excavation width, excavation depth, soil shear strength, wall embedment depth and wall thickness were varied to generate maximum wall deflection and to study the wall deflection behavior. Eight excavation case histories of deep excavation in thick layers of clays was adopted for generation of data used for development of intended model as a basis of numerical analyses. This research used extensive plane strain (2D) analysis to examine the wall deflection for excavation-induced ground deformation in clay deposits supported by diaphragm wall and bracing, using the Finite Element Method (FEM). For the development of the Simple Polynomial Regression models for estimating the maximum wall deflection, a database of excavation case histories are compiled and to complement the database of excavation case histories, a large number of data was generated using FEM solutions, by varying the principal parameters considered in the study including excavation depth, excavation width, soil shear strength, embedment depth and wall stiffness with Mohr coulomb soil model. Based on the established database, a Simple Polynomial Regression model is developed for predicting the maximum wall deflection, caused by braced excavations in clays. The proposed method provides a fairly good prediction of wall deflection as compared to FEM. A Simple Polynomial Regression models has been proposed to estimate the lateral deflection of wall braced excavation in clay with average to good workmanship. Computed values by SPRM (simple polynomial regression model) agreed well with results from observed maximum wall deflection from different excavation case histories which are not used in the development of simple model.
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    Stabilization of Expansive Subgrade soil using Waste Ceramic Powder ( A case study on the road segment in Ethio ICT Village)
    (Addis Ababa University, 2019) Bililign, Firdawek; Samuel, Tadesse (PhD)
    Subgrade materials are expected to have basic desirable characteristics related to strength, stiffness and swelling. If these properties are not fulfilled, engineers are expected to come up with ground improvement methods. The growing cost of traditional stabilizing agents and the need for the economical utilization of industrial and agricultural wastes for beneficial engineering purposes have prompted an investigation into the stabilizing potential of waste ceramic powder in highly expansive clay soil. This research work is aimed to evaluate the suitability of waste ceramic powder for stabilization of expansive clay soil. The preliminary investigation of the soil to be stabilized shows that it belongs to A-7-5 class of soil in the AASHTO soil classification system. Soils under this class are generally of poor engineering use. Atterberg limits, free swell, free swell index, free swell ratio, compaction and CBR tests were used to evaluate properties of stabilized soil. The soil was stabilized with waste ceramic powder in stepped concentration of 5%, 10%, 15%, 20%, 25% and 30% by dry weight of the soil. All stabilized soil samples were also cured for 7 days for Atterberg limits, compaction and CBR tests. Analysis of the results shows that slight improvement on the geotechnical properties of waste ceramic powder stabilized soil. Waste ceramic powder reduces plasticity index, swelling and CBR swell and it increases MDD with decrease in OMC and CBR. Curing has an insignificant effect on the geotechnical properties of waste ceramic powder stabilized soil. From this study it was found out that waste ceramic powder stabilized soil do not show significant change for both index and strength property. Additional study is also incorporated as a supplementary work to investigate the effect of applying 3% lime as an activator in combination with 15% waste ceramic powder on the geotechnical properties of the soil for uncured and cured soil samples. The results indicate that lime in combination with waste ceramic powder is suitable for improving the plasticity index, swelling and CBR. The strength values (CBR) also increased with curing ages, thus indicating that the blend has a potential for time-dependent increase in strength that will reduce the quantity of stabilizer needed for the construction of roads over the expansive soil. Therefore, this study shows that lime in combination with/plus waste ceramic powder can be effectively used to improve expansive soils with low soaked CBR value and high plasticity.
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    Stabilization of Soil Block Masonry with Pumice
    (Addis Ababa University, 2018) Ekram, Anwar; Samuel, Tadesse (PhD)
    The old traditional earth block methods of construction are currently reconsidered as a very environmentally friendly alternative to modern buildings due to the advantages they provide, such as the complete recycling of materials, low energy consumption during the manufacturing process and service life, as well as the comfort and health aspects of people living in them. Soil is widely used in the traditional construction of mud houses called “Chika bet’’. Soil as a building material is available in most areas of the country. The weak sides of earth block masonry such as low bearing capacity and low resistance to moisture have been overcome by stabilizing it with pumicite/volcanic ash. The compressive strength of the mud blocks increased by the pumicite. This thesis studies the effect of the proportion between the soil and the stabilizers (such as pumicite and straw fiber) on stabilized earth blocks strength. It also compares mechanical properties (compressive strength and absorption) of stabilized earth blocks which are prepared using only local soils (which is taken from Adama, Boku area) and with the addition of stabilizers (pumicite and straw fiber). This research provides detailed technical information on suitable soil types for stabilized earth house construction, stabilizers and production of stabilized earth blocks. Related literatures review show that soil types, proportions between soil and amount of stabilizer and compaction pressure applied to the moist soil mix affects the quality of the stabilized earth block. In this study pumicite/volcanic ash is used as a stabilizing agent. It is highly porous volcanic rock and highly deposited in Bulbula, Ziway area. Soil from Adama was the target for testing and investigation.Laboratory tests were conducted on Boku area soil and provided detailed information on the soil grading and other engineering properties of the natural soil. The result was compared with standard values to verify suitability of the soil for soil stabilized earth block production. It is possible to determine the suitability of other area soils by applying the same technique. Using soil from Boku area of Adama and stabilizers (pumicite and straw fiber), ten different types of samples were prepared. Tests were conducted on these samples in order to evaluate their performance such as compressive strength and total water absorption capacity on which the durability of the blocks depends. The effect of the pumicite and the straw fiber content in stabilized mixture was evaluated and comparisons were made for all block samples. The investigation has revealed that, out of all block samples, blocks which are produced from 10% pumicite (10P), 10% pumicite with 3% straw fiber (10P3S), 10% pumicite with 6% straw fiber (10P6S) and 10% pumicite with 9% straw fiber (10P9S) have total water absorption values that fulfills the recommended value. This research could help in providing possible solution for adequate shelter problem in Adama and in Ethiopia in general and to overcome some defects of mud blocks.
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    Study on The Design Methods of Tall Wind Turbine Foundation (A Case of Adama I Wind Farm)
    (Addis Ababa University, 2019-04) Bizu, Melesse; Samuel, Tadesse (PhD)
    Wind energy has been deemed an appropriate means of diversifying Ethiopia’s energy mix while simultaneously addressing the deficit in electricity supply which the country faces. The first wind farm in Ethiopia is Adama I wind farm, which generates a 51MW of energy using 34 sets of wind turbine generators. The foundation supporting the wind turbine generators is designed assuming the load encountered to be static; however, wind turbine structures are inherently dynamic structures, and the design of foundations for resistance of dynamic loading requires a different design approach other than static approach. Both the static and dynamic foundation design approach for wind turbine structure are studied in this project. When designing the foundation taking into account the dynamic nature of the structure, the final design resulted in the circular gravity base foundation with a bottom diameter of 13.2 m, and depth of 3m. The reduction in dimensions of one particular foundation is interpreted by the change in volume of concrete, which showed a decrement of 124 m 3 when compared with the existing typical foundation in Adama I wind farm. Moreover, the foundation design to support all the 31 turbines is identical across 5km stretch of wind farm land, and didn’t cater to the local soil or rock condition. In reality, the ground condition is different across the wind farm land; as result, the effect of using different bearing capacity values on foundation dimension is also explored. The final design resulted in the circular gravity base foundation with a bottom diameter of 14 m, and depth of 2.5 m for all the bearing capacity used in the study. The reduction in dimensions of one particular foundation is interpreted by the volume of concrete, volume of backfill. The volume of the concrete showed 115 m 3 decrement; the backfill material decreased by 1,137 m 3 when compared with the existing foundation in Adama I wind farm. The results of this part of study show that the increasing the bearing capacity had negligible contribution in reducing the dimensions of the foundation. This project concludes that the bearing capacity is not the major limiting factor when designing a foundation for the Adama I wind farm. The stability against overturning is the most critical criteria for both the static and dynamic approaches. Furthermore, when designing wind turbine foundation taking into consideration the soil structure interaction and dynamic nature of the wind turbine generators, the foundation dimension showed a decrement, which emphasizes the static approach to foundation design is conservative.
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    Study the Physical Characteristics and Severity to Collapse of Collapsible Soils: A Case of Turmi – Omo Road Project
    (Addis Ababa University, 2019-11) Endalk, Fentie; Samuel, Tadesse (PhD)
    Collapsible soils present significant geotechnical and structural engineering challenges for different types of constructions. These soils suffer volume changes and collapse deformation upon wetting. Situations in arid and semi-arid climates favor the formation of the most problematic collapsible soils. Almost all naturally occurring collapsible soil deposits are debris flows, rapid alluvial depositions, and wind-blown deposits (loess). If unrecognized, it may cause pumps or deep sinkholes, which leads to traffic accidents and loss of lives. Hence, this research was conducted to investigate the physical properties and the severity of collapse of the soils found in the road project of Turmi - Omo. To achieve the objective of this research, papers, journals, actual design reports, contract document of the project and different books have been scrutinized under literature review, samples from the research area were collected from different test pits below the natural ground level, and then laboratory tests for index properties and oedometer tests have been carried out using disturbed and remolded samples. From the test results the subgrade soil classes fall in A-4, A-6 and A-7-6 according to AASHTO classification. In addition, according to USCS the soils under investigation are classified as ML (group of inorganic silt of medium compressibility). The evaluation of susceptibility of soil to collapse was measured by performing single oedometer tests on samples remolded at their in-situ densities and at maximum dry densities. The oedometer test results at the investigated depth of soil showed that, the collapse potential of samples remolded at their in-situ densities and natural moisture contents is within the range of 1.49 % to 5.93 % and that indicates that the severity of collapse is slight to moderate. And also, the collapse potential of samples remolded at their maximum dry densities and optimum moisture contents is within the range of 0.19 % to 0.495 % and thus the severity of collapse is very slight. Though the results indicated that the severity to collapse is very slight, the soil in the investigated section is collapsible and the collapse potential could be significantly reduced by compaction during construction.
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    Supplementing Site Investigation Techniques of Earthworks and Sub Grade Soils with Geophysical Investigation in Road Designs
    (Addis Ababa University, 2013-10) Ashenafi, Tsegaselassie; Samuel, Tadesse (PhD)
    In the construction of road projects in Ethiopia, one of the main factors for the delay and increase in cost of road construction projects is huge variation of earthwork item and quantities. This caused the concerned authorities problems of budgetary, questioning of design documents, untrustworthiness on consulting offices, etc. The purpose of this research is to necessitate the use of geophysical investigation in an attempt to reduce the discrepancy of earthwork quantity and project cost between the design and construction phases. In order to have sufficient data for the study, records of already designed roads that are not yet constructed or under construction are collected from reliable sources (Ethiopian Roads Authority and International and Local consulting offices). Those data are verified or compared at selected sections (particularly deep cut sections) of the project road using geophysical investigation in the field. Comparison is also made between the experimental results obtained with the help of geophysical investigation and data collected from the already designed roads. Based on the results found from the data presentation and discussion, it is observed that lack of detailed site investigation using appropriate method caused major cost overrun and delays in several road projects. Thus, by studying the area of interest with respect to the required subsurface investigation, planning an exploration technique on a sound geotechnical basis using the test pits supplemented by geophysical technique would bring cost effective result with better accuracy.