Geotechnical Engineering

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Effects of Different Fillers on the Mechanical Properties of Hot Mix Asphalt
(AAU, 2015-11) Nigatu, Wudineh; Alemayehu, Teferra (Prof.)
Asphalt concrete road construction is a crucial part of the Growth and Transformation Plan (GTP) of Ethiopia for building a high performance transportation networks for its economic development. Currently many asphalt concrete road construction activities are taking place, especially on trunk and main access roads. In this study the effect of different types of mineral fillers and their proportion at a given filler percentage by total weight of the mixture in hot mix asphalt concrete performance are investigated and alternative filler proportions are proposed for the construction of asphalt concrete pavement for Gambella –Itang –Jikawo road and it will serve as a guide to use alternative fillers for construction of asphalt concrete pavement in Ethiopia. Investigation was made to adjust the Job Mix Formula using different filler proportion under the project specification. The mineral fillers, with given percentages by total weight of the mixture, used in this study were crushed stone, Pagag Sand, Cement and Marble dust passing 0.075mm sieve. After determining the optimum bitumen content with Marshall Stability test a number of trial mixes have been performed using the Marshal Mix design procedure to arrive at asphalt concrete mixtures that fulfill the Marshal criteria. The effects of each mineral filler type on Marshal Properties of the asphalt mixtures at a given optimum asphalt content 5% were evaluated and possible basis for such difference in properties was discussed. Results of this study indicate that the addition of cement and marble dust to asphalt concrete as filler has produced relatively the same comparable Marshall properties. However, the Marshall Stability property obtained from replacement of these fillers was not good as compared with Pagag sand (natural sand). It can be concluded that Pagag sand replacement up to 50% in the mixture shows acceptable air voids, Marshall Stability and flow values and maximum VMA values. However, from the VFA values we can understand that the replacement of Pagag sand by more than 10% shows a decrease in values below the specification limit as the result of air voids increases when the Pagag sand in the mixes increases that indicate the mixture needs more than 5% asphalt content which is not economical. The use of cement 50% from the total proportion of design filler content (8.06%) in the mixture satisfies all the Marshall Properties. However, increasing the more than 50% replacement in the mixture test result shows it fulfills the Marshall properties under the project specification except the stability requirement. It is also observed that the Marshall Stability values obtained from cement filler is not uniform when we increase the replacement proportion. This may be due to creation of stabilization that leads to shrinkage cracking or asphalt stiffening effect. Since the cement filler Marshall Stability property obtained is not uniform, it would be difficult to give an explanation on this property based on this laboratory investigation only. The results of this research work may be used as basis for further detail investigation on the effects of mineral fillers especially cement and marble dust on Marshall Stability and Flow properties of hot mix asphalt.
Investigation into Some of The Engineering Properties of Soils Found in Mojo Town
(Addis Ababa University, 2016-12) Mastewal, Getahun; Alemayehu, Teferra (Prof.)
Today Mojo has expanded considerably with new buildings, railways, roads, industriesand dry port. Therefore, a better understanding of the subsoil is required. It is also worthmentioning that, Mojo is located in the rift valley of Ethiopia thus placing it in seismic activzone. According to EBCS 8, 1995 the city is located in zone four This research work is carried out to investigate the static engineering properties of MojoTown. To achieve this objective, soil samples were collected throughout the town andlaboratory and field tests were conducted. According to results of the field test, the in-situ density ranges from 1.40 to 1.70g/cmand the dry density have a value from 1.12 to 1.61g/cm3. From the grain size analysis result, the soil of the town has clay content ranging from 10.03 to 32.32%, silt fraction from 36.82 to 80.65%, sand fraction 5.77 to 92% and gravel content from 0.0 to 18.77%. The Atterberg limit test on the research area showed a liquid limit range from 29 to 87%plastic limit ranging from 18 to 50% and plastic index from 11 to 46%. The specific gravity ranges from 2.62 to 2.70 and the Free swell ranges from 20 to 60%From the compaction test result the maximum dry density (MDD) of Mojo soil ranges from1.15 to 1.83 g/cm 3 and the optimum moisture content ranges from 14.57 to 44.33 %. According to Unified Soil Classification System (USCS), The research area shows wide range of category which include silt, silt with sand, sand and sandy silt with gravel From the Direct shear test results which is conducted on representative samples collectethe research area have angle of internal friction ranging from 12 0 to 0 29 From the unconfined compression tests, Mojo soil unconfined compressive strength (qu), ranges from 135 to 179 kPa, Undrained Shear Strength (cu), ranges from 68 to 90 kPaand the research area have stiff consistency. Finally, from consolidation tests the soil in the research area is over consolidated in itnatural state with compression index ranging from 0.3 to 0.32, coefficient of consolidation ranging from 0.24 to 0.82 and coefficient of permeability ranging from 1.83 to ⁄ 23.4710 ⁄
Investigation into the Index Properties and Swelling Potential of Expansive Soils of Sheno Town
(Addis Ababa University, 2021-01) Michael, Bekele; Alemayehu, Teferra (Prof.)
In this study the index properties and swelling potential of soils of Sheno town are examined. The study is conducted with the aim of examining the index properties which are relevant in predicting the swelling characteristics of soils of the study area. Expansive soils of Sheno town, both the black soils as well as the light brown soils undergoes considerable swelling during the wet season. The test results of soils of Sheno town showed that the specific gravity ranges from 2.66 to 2.86. The index property tests showed that the plasticity index ranges from 60% to 78.9% at a depth of 1.5m and 45.2% to 58.2% at a depth of 3.0m.The unconfined compressive strength of soils of the study area ranges from 72kPa to 83kPa at a depth of 1.5m and 82kPa to 93kPa at a depth of 3.0m.The clay content of the soil ranges from 58.47% to 75.0%at a depth of 1.5m and 45.68% to 58.77% at a depth of 3.0m. Free swell tests conducted on the collected samples showed a range from 123% to 165% at a depth of 1.5m and 83% to 120% at a depth of 3.0m.The results of the one-dimensional consolidometer showed that the swelling pressure of the area ranges between 70kPa to 200kPa, the pre-consolidation pressure (Pc) ranges between 150kPa to 290kPa and the compression index (Cc) ranges between 0.285 to 0.389. Soils of the study area are classified both by the USCS and the AASHTO system. According to the USCS, soils of the study area fall in the CH group and when using the AASHTO system all soils fall in group A-7 which cannot be used as sub grade for highway constructions.
Optimum Design of Highway Cut Slopes in some Selected Soils found in Ethiopia
(Addis Ababa University, 2010-12) Asfaw, Hussien; Alemayehu, Teferra (Prof.)
This thesis presents the safe and economical highway cut slope design in some selected soils found in Ethiopia. The preparation of the standard has been carried out by determining the soil shear strength parameters in the laboratory and determining the safe and economical slope using the factor of safety contour charts. In this work, first, factor of safety contour charts are produced. Using these charts existing slopes are assessed. In addition to collecting soil parameters from previously analyzed soil samples, three soil samples were collected for laboratory analysis. Using the compiled soil parametes and prepared factor of safety contour charts, cut slope standard tables are prepared for the different soils. Lastly, the output of this standard is compared with ERA 2002 cut slope standard for cost – benefit analysis. Generally, it has been observed that the newly developed highway cut slope standard is safe and economical. For the cases investigated in this work, the reduction in cost ranges from 19 to 32% f that of the current ERA 2002 standard.
The Potential Use of Cinder Gravel as A Base Course Material When Stabilized by Volcanic Ash and Lime (The Case of Metehara Area)
(2015-10) Zerai, Hadera; Alemayehu, Teferra (Prof.)
This study has been carried out in order to determine the optimum blending proportion of cinder gravel with volcanic ash and lime. In this regard, an investigation into the improvement of the natural cinder gravel by stabilization technique was conducted using samples collected from Metehara area. In the first phase of investigation, mechanical stabilization was carried out at various proportions of volcanic ash blended with cinder gravel. Compaction method was used in the determination of the optimum amount of volcanic ash that makes up the deficiency of fine particles. In this method, the optimum amount of volcanic ash has been found to be 22% by weight. CBR values of soaked and unsoaked conditions were determined for cinder gravel stabilized mechanically with the indicated optimum amount of volcanic ash at 3,7,14 and 28 days of wrapping the sample in the mold with a polyethylene sheet. The test results showed that the CBR values for all of these days of wrapping the sample in the mold were more than 80% which is the requirement of ERA specification for road base while that of the cinder gravel alone was found to be 72%.However, the CBR values were, more or less, not affected by the duration of wrapping the sample in the mold. In this phase, the CBR value for the soaked condition has been found to be less than that of the un soaked condition as expected. In the second phase of investigation, mechanical as well as lime stabilization was carried out simultaneously in which 20% of volcanic ash and 2% of lime were blended with cinder gravel in order to find out how the CBR would be changed. Soaked and un soaked conditions at 3,7,14 and 28 days of wrapping and keeping the sample in the mold indicated that the CBR values in this phase were larger than the corresponding values obtained by blending cinder with volcanic ash only. The CBR value in this scenario was observed to increase with duration of wrapping and keeping the sample in the mold unlike the first phase. Furthermore, the CBR value after four days of soaking was found to be greater than that of the un soaked condition for a given duration of wrapping the sample in the mold. Although laboratory investigation in the present study has confirmed that the stabilized cinder gravel can be used as base course material, field performance of this stabilized material should be investigated on a pilot project.
Predicting the value of CBR from DCP for Addis Ababa Red clay
(Addis Ababa University, 2014-11) Ermias, Genye; Alemayehu, Teferra (Prof.)
The research attempts to introduce the Dynamic cone penetration (DCP) to replace CBR test in preliminary design stage. DCP is a simple test device, portable and easy to operate and a repeated test can be conducted as much as desired to achieve a better and reliable design parameter. Field DCP test with in situ density test were conducted. Disturbed and undisturbed samples were taken to the laboratory with which natural moisture content, Atterberg limits, grain size analysis, free swell, standard proctor density test and CBR were conducted. After looking thoroughly the scatter diagrams, it is found out that DCPI is influenced by in situ moisture content and bulk density however it is not influenced by Atterbeg limits. It is also found out that there is good relationship between DCPI and CBR. Different techniques are used to find an expression that best suits to find the value of CBR from DCP and other parameters. The final accepted one is the expression developed by using two stage residual inclusion estimation using liquidity index as variable The result gives the following equation with N=36 and adjusted coefficient of determination of 0.633.Predicted DCPI=0.207*LI + 22.571 CBR=-0.142*DCPI-0.18(DCPI-Predicted DCPI) +7.701
Shear Modulus and Damping Ratio of Dry Koka Sand Using Cyclic Simple Shear Test
(Addis Ababa University, 2010-06) Girmachew, Yimer; Alemayehu, Teferra (Prof.)
The nature and distribution of earthquake damage is strongly influenced by the response of soils to cyclic loading, and the behavior of soils subjected to dynamic loading is influenced by dynamic soil properties. The determination of these dynamic soil properties is invaluable in the response analysis of soils to cyclic loading. Of these dynamic soil properties, shear modulus and damping ratio are the most important; and this paper is concerned with the determination of the shear modulus and damping ratio of sand. In this research the shear modulus and damping ratio of Koka sand is determined using the cyclic simple shear test. The results have shown that the obtained normalized shear modulus values are located lower than those suggested in literature, especially at lower strains. For higher strains the obtained normalized shear modulus values agree with those suggested in literature. The obtained damping values are almost within the range suggested in literature.
Software Development for the Analysis of Lateral Earth Pressure and Design of Retaining Walls
(AAU, 2015-08) Ermias, Tamirat; Alemayehu, Teferra (Prof.)
Analysis of lateral earth pressure is one of the basic tasks that a geotechnical engineer deals with while analyzing or designing earth retaining structures. In the design stage, the lateral earth pressure should be estimated accurately and stability of the retaining structure be checked for different destabilizing factors. In order to analyze/design the earth retaining structure practicing and academic professionals have to go through tiresome and routine step by step procedures. Usage of commercially available programs to tackle these problems would be an ideal solution. However, such applications are costly and wouldn’t be the choice of professionals in developing countries, like Ethiopia. Different theories have been suggested by different authors to compute the lateral earth pressure that soils exert on retaining structures. Earth pressure theories suggested by Coulomb and Rankine are the most well known and termed as ―Classical Earth Pressure Theories‖. These theories have been considered reliable in spite of the limitations they have and are considered basic to the problem. One of the major drawbacks of the theories is that they assume the failure surface to be plane throughout. As time goes by, these theories have been modified to suit the different actual conditions and come up with better results. Bell (1915) has further developed Rankine’s equation to handle cohesive soils. Kerisel and Absi (1990) have developed a chart putting in to account that, the failure plane has got a logarithmic spiral at its bottom portion together with a tangent extending further to the ground. This thesis aims at developing software for the analysis of lateral earth pressure and design of gravity and cantilever retaining walls for external stability based on the theories suggested by; Coulomb, Rankine, Bell and Kerisel and Absi. The developed software, GeoLEPARD, helps in analyzing earth pressures and getting the right retaining structure dimension fast and simple. Outputs of the software have been compared against results of hand/spread sheet calculations. The comparison has shown that, with proper data entry, the software can generate similar output enhanced with numeric and graphical displays.

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