Geotechnical Engineering

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An Alternative for Stabilization of Addis Ababa Expansive Soil By Crushed and Natural Sand
(Addis Ababa University, 2016-06) Simon, Hiwot; Teferra, Alemayehu (Professor)
In this thesis, an alternative for stabilization of expansive soil by crushed and natural sand were examined separately. The test results revealed that there is a significant improvement on soil consistency. The classification of the mixed soil is altered from CH to MH group for both types of sand blended. Additionally, the swelling potential and swelling pressure reduced considerably. However, the groups of the mixed soil remain under the group of A-5-7 for all proportion of the sand-soil mixture. For higher proportion of mixture a considerable improvement was attained in the value of unconfined compressive strength. Nevertheless, there is no marked progress achieved in the soaked CBR value. Finally, after making cost comparison for both types sands, 40% sand by weight of soil has showed a cost reduction when compared to total soil replacement. AN ALTERNATIVE FOR STABILIZATION OF EXPANSIVE SOIL OF ADDIS ABAB BY CRUSHED AND NATURAL SAND
Analysis and Parametric Study of Piled Raft Foundation Using Finite Element Based Software
(Addis Ababa University, 2009-05) Abate, Simeneh; Teferra, Alemayehu (Professor)
The design of group piles depends on either the group or single pile capacity of piles. In conventional design method of such foundations, the stiffness of the pile cap is barely taken into account. Such design becomes too conservative if the pile cap is in contact with the ground. Because the pile cap contributes in transferring load to the ground and distributing load over the piles. The design method that considers the contribution of the pile cap and interaction between the different elements of group piles is called piled raft foundation. The concept of piled raft foundation leads to economical design. In this paper, analysis and parametric study of piled raft foundation has been conducted. The study is performed using powerful finite element based software, PLAXIS. A number of parameters were selected from the elements of the piled raft system. According to their effect on the response of piled raft system, some are taken to be constant while others are varied. Among the varied parameters, raft thickness, pile length, pile spacing and pile number were considered. Other possibilities were also investigated in search of an optimum placement of piles. The analysis results from the PLAXIS software have shown a close prediction to that of in-situ measurements and other numerical methods. From the parametric study, concentrating piles around the center for uniformly loaded rectangular piled raft foundation reduce the differential settlement.
Analysis of Gidabo Earth Fill Dam by Introducing Geotextile Reinforcement
(Addis Ababa University, 2015-11) Yilekal, Ashenafi; Teferra, Alemayehu (Professor)
Soil reinforcement is now well established technique for geotechnical applications in most parts of the world. This thesis includes the application of soil reinforcement technique for slope stability of earth fill dams. The dam section designed by WWDSE has been considered for the case study. The slopes of dam are then considered to be reinforced with horizontal layers of geotextile and the percent improvement of factor of safety under static loading has been studied. The statically optimized section has been checked for stability against dynamic loading. The analysis is carried out by state of the art software package, Geo-Slope software. It is found that much steeper slopes may be provided to the earth dams by providing geotextile reinforcing layers. The suitable length of reinforcing layers, spacing between them and offset from the face needs to be determined for the required slopes of dam. The statically optimized section is found to be stable against the earthquake loading. This technique may be particularly useful for high earth dams and may result in lesser construction cost as well as construction time. KEYWORDS : geotextile reinforcement,earth fill dam, reinforced slopes,dynamic analysis, earthquake, Geo-Slope software
Analysis of Strip Plates on Elastic Foundation Using Generalized Subgrade Model
(AAU, 2018-06) Amlesu, Teklebrhan; Asrat, Worku (Asst Prof.)
A concrete plate supported directly by the soil continuum is a very common construction form. The response of the plate when it carries external load is influenced by the soil, and the response of the soil is also influenced by the action of the plate under the load. Thus, developing a subgrade model for soil-structure interaction problem is essential in order to predict the response of both components of the system and arrive at an optimum design. Many subgrade models have been developed in order to improve on the inherent lack of shear interaction among the individual springs found on the long-enduring model of Winkler. Moreover, these models still have shortcomings with the nature of simplifying assumptions they make to ease the mathematical equation. Recently a generalized model is presented for a subgrade idealized as an elastic layer overlying a rigid base. In contrast to previous works no stresses, strains or displacements are neglected a priori. The main objective of this work is implementing, verifying and calibrating this improved continuum-based generalized subgrade model in the analysis of strip plates on an elastic foundation. The governing differential equation of a strip plate on elastic foundation is formulated. Then, closed form particular solutions, when using Winkler type and Kerr equivalent Pasternak models, are obtained by considering different boundary conditions of long and short length of a strip plate, under different loading conditions. Microsoft excel programs are written for the computation of deflection, moment and shear force. The subgrade models are then calibrated using Finite Element based Plaxis 2D software. Lastly, numerical illustration is provided using these models in comparison with Plaxis 2D model for long and short strip plates subjected to selected symmetrical loading conditions. The result of the comparison shows that the calibrated variants give good outcome in agreement with FE outputs. Consequently, these findings display that the calibrated models can be used in routine analysis of strip plate on elastic foundation and also can be incorporated in commercial software.
Application of a Generalized Subgrade Model in the Analysis of Circular Plates on Elastic Foundations
(AAU, 2018-06) Meron, Alebachew; Asrat, Worku (Asst Prof.)
The solution to the problem of beams and plates on an elastic foundation has been attempted in the past using various subgrade models developed by many researchers, one of the pioneers being Winkler. Most recently, a new calibrated and more advanced multifaceted continuum foundation model has been presented by Worku without neglecting any stress, strain, or deformation component in the continuum unlike previously proposed models. The study of interaction between a plate and an elastic medium has useful applications in geotechnical engineering. This research investigates the use of a generalized continuum subgrade model of Worku for analyzing circular plates resting on an elastic foundation. The approach employed is both analytical and numerical. In the analytical work, the governing differential equations of an axisymmetric circular plate on a homogeneous elastic foundation has been formulated that incorporates Winkler and Pasternak-type subgrade models. Closed form particular solutions have been presented for different loading conditions of small and large circular plates after obtaining a general solution of the differential equations. A math solving software (i.e. Mathematica) is used to compute the deflections and internal actions in a spreadsheet program due to the complexity of the functions. In the numerical study a FEM based software (i.e. PLAXIS 2D) is used to calibrate the analyzed circular plate using the presented models by seeking adequate agreements with the FE outputs. At last, numerical examples are solved using these models and compared with PLAXIS 2D for small and large radii circular plates of some loading conditions. From the plots of the outputs, it is observed that the generalized models of Worku are suitable and more appropriate than classical models to analyze circular plates on elastic foundations.
Application of a Rigorous Subgrade Model in the Analysis of Rectangular Plates on an Elastic Foundation Using Finite Difference Method
(Addis Ababa University, 2019) Tofik, Seid; Asrat, Worku (PhD)
Plate on elastic foundation establishes an adequate idealization in the analysis of shallow foundations, which includes isolated footings, combined footings, mat foundations, and flexible pavement. The important issue in the analysis is modeling the contact between the plate and the soil medium that is a soil-structure interaction (SSI) problem. The primary difficulty in the analysis of the soil–structure interaction lies in the determination of the contact pressure. The simplest subgrade model is the single parameter Winkler mechanical model, which represents the foundation soil by a series of independent springs. Winkler model is widely used and practiced in spite of its deficiency in representing the continuous behavior of real soils. Later, many advanced mechanical subgrade models have been proposed in order to improve on the inherent lack of shear interaction among the individual springs. However, these models still have their drawbacks in that they do not represent the subgrade shear interaction adequately. With the objective to improve on such drawbacks, a generalized continuum-based model has been recently proposed by Worku. This generalized subgrade model satisfies the fundamental elastic laws and all the boundary conditions since it is derived by considering all stress, strain and displacement components. The main objective of this work is to implement and calibrate the generalized continuum based subgrade model for the analysis of rectangular plates on an elastic foundation. The governing differential equation of a rectangular plate that incorporates Pasternak type subgrade model is formulated. Thus, an ordinary finite difference method is developed to solve the partial differential equations. Code based on MATLAB ® programming language is writ- ten for determining deflections and internal actions of the plate. Finite Element based software is used as a tool to determine an adjustment factor for the generalized model. Finally, the proposed method has been validated by comparing the results with other numerical models for selected loading conditions. The results of the comparison show that the generalized model shows an excellent agreement with the FE outputs and capable of predicting the behavior of the rectangular plates on elastic foundations.
Application of Gis And Remote Sensing for Flood Hazard and Risk Analysis: The Case Of Boyo Catchment
(Addis Ababa University, 2009-06) Gobena, Destaye; Suryabhagavan, K.V (PhD)
Flood is a natural phenomenon that will remain a major hazard as long as people live and work in flood prone areas. It occurs when the volume of water in a river or stream exceeds the capacity of the channel. It also takes place along lake when higher than normal water levels inundate low-lying areas. The present study was carried out to identify and delineate flood hazard and risk zones in the study area. In order to do this, it was found important to understand the catchment characteristics, and hence flood hazard assessment was done to the whole Lake Boyo catchment area. An integrated Remote Sensing and GIS approach was found to be very helpful to delineate flood hazard and risk zones in the study area. Factors that were found to be significant in triggering flood hazard in the study area in decreasing order of importance were: drainage, elevation, geomorphology, land use land cover, rainfall and slop. These factors were weighted in hierarchical order using the MCE approach to produce flood hazard map of the catchment. From the flood hazard map, the areas of flood hazard levels were calculated. Since all the areas of the very high and more than 90% of high flood hazard levels are found in Shashogo Woreda, flood risk analysis was done for the Woreda using the two elements at risk, viz., land use and population density of the Woreda. Major findings of the study revealed that, PAs in the down stream part of the catchment: Doesha, Mololicho, Shemo, Biramora, Musagesa, Urbecha and Kemetcho Borara PAs were subjected to very high flood hazard and risk and the different land uses in these areas are within high to very high flood hazard and flood risk level.
Application of Marble Dust to Improve the Engineering Properties of Expansive Soils to be used as Road Bedding Material
(Addis Ababa University, 2016-12) Mada, Tagel; Tadesse, Samuel (PhD)
Expansive soils are characterized by volume change due to variation in moisture content. The cyclic wetting and drying process causes vertical and horizontal movement in expansive soils leading to failure of civil engineering structures found on such soils. The problematic nature of such soils can be improved by employing chemical stabilization techniques such as lime, cement and enzyme stabilization. However, as these techniques are expensive to developing countries such as Ethiopia, locally available low cost materials can be applied as alternative to improve the engineering properties of expansive soils. In the present research work, the performance of marble dust to improve the problematic nature of expansive soils is investigated. The study is carried out on a highly expansive soil section of selected road project. The natural subgrade soil obtained from the highly expansive section of the road is characterized for its engineering and strength properties and it is found to be highly expansive soil with low bearing capacity, high swell and characterized as A-7-5 according to the AASHTO classification and rated as poor (unsuitable) subgrade material. The expansive subgrade soil is blended with increasing percentage by weight (5% to 30%) and the improvements in engineering properties are studied and it is noted that it improves with increasing percentage of marble dust and with increased periods of curing though it is not significant as compared to specification requirements of several standards. With the higher percentage of marble dust (30%), the swelling potential of the natural soil changed from ‘High’ to ‘Medium’, LL reduced from 88% to 63%, PI reduced from 52% to 34%, CBR increased from 0.9% to 2.25% and the CBR swell reduced from 8.6% to 5.3%. Un-soaked CBR test is conducted on the natural subgrade soil and the 30% marble dust blended sample and it has been noted that the subgrade class improves for both indicating significant reduction in project cost as result of reduction in pavement thickness. Thus, marble dust can be recommended as an alternative stabilizing agent for expansive soils by itself or being blended with small percentage (1-3%) of effective stabilizing agents such as lime so that significant project cost reduction and minimal environmental degradation can be assured.
Applications of Bamboo as a Sub Grade Soil Reinforcements (Ziway-Hawassa Road), Ethiopia
(Addis Ababa University, 2017-03) Zerihun, Gosaye; TADESSE, Samuel (PhD)
Road construction on fine grained soils are challenges to geotechnical engineers and designers because of its low bearing capacity which results in cracks in the pavement structure as well as increase in the thickness of the pavement. Use of natural fiber in geotechnical engineering for improving soil properties is advantageous because they are cheap, locally available, biodegradable and eco-friendly and causes significant improvement in tensile strength, shear strength, and other engineering properties of the soil. This thesis work is aimed to evaluate the applications of bamboo as a subgrade soil reinforcements. The soil samples was collected from Ziway town and Bamboo sample was collected from Hagere selam. Two test pits of soil samples were collected for the investigation purposes but tests on reinforced soil were conducted on only one selected test pit. The preliminary investigation of the soil on index properties shows that it belongs to A-4 class of soil in the AASHTO soil classification system and ML under USCS system. Compaction, direct shear and CBR tests were used to evaluate properties of bamboo reinforced soil. The soil was reinforced with bamboo in percentages of 0.25%, 0.5% and 1% by dry weight of the soil and length of 15mm, 30mm and 45mm with a maximum thickness of 3mm to 5mm.Certain percentages of bamboo with varying lengths are used for the experimental investigations. All bamboo samples were treated by a certain amounts of kerosene by mixing it with kerosene to avoid the absorption of moisture. Water absorption test shows that the water absorption of bamboo coated by kerosene was decreased by about 20%.Soil samples were prepared at its MDD corresponding to its OMC to conduct direct shear and CBR tests with and without reinforcements. Analysis of test results shows that bamboo reinforcements of soil reduces MDD very slightly while OMC remains more or less the same. Bamboo reinforcements of sandy silt soil has no significant effects on shear strength parameters (C and Ø) but significantly increases CBR (i.e.CBR increases by about more than 200% of that unreinforced soil) at 1% of 45mm. Generally the CBR value of sub-grade soil increases significantly with the inclusion of bamboo but different factors such as removal of bamboo (environmental cost), transporting of bamboo (transportation cost), preparation of bamboo (technical cost), decomposition of bamboo makes the design un-economical and as the sub-grade soil is sandy silt it is better to improve its engineering properties by compaction only.
Assesment of Damage of Buildings Constructed in Expansive Soil Areas of Addis Ababa
(Addis Ababa University, 2004-10) Sisay, Afewerk; Haile, Messele(DhD)
The amount of damages caused by expansive soil is tremendously high and alarming. These damages are mainly dominated in light weight-engineering structures founded in expansive soils. These structures include lightweight buildings, roads, runways and buried utilities. The problem associated with expansive soils is not yet properly solved. It is important to assess buildings constructed in expansive soil areas in order to know the cause of failure. This helps in providing solutions for newly constructed buildings and to get remedial measures for those already damaged. Therefore, in this study an attempt was made to assess the damage that occurred on buildings that are constructed on expansive soil areas by taking ninety six randomly selected houses in the city of Addis Ababa. The houses are located in Bole, Olympia, Nifasilk, Lafto, Old Airport, Mekanisa, Gergi and Bole bulbula localities of the city. The study showed that 64 % of the houses suffered heavy damage, 8 % of the houses were slightly damaged and 28% of the houses showed no damage. Analysis was made to understand the cause, extent and type of damage that was observed in the houses. The damages that are observed are mainly caused by poor design, construction and non-controlled drainage. Detailed investigation was made for the Ethiopian Airlines maintenance hangar building which has shown pronounced failure in both the sub structure and the super structure Finally, conclusion and recommendations are made.
Assesment of Damage of Buildings Constructed in Expansive Soil Areas of Addis Ababa
(Addis Ababa University, 2015-11) Fikadu, Aklilu; Tadese, Samuel(PhD)
Under the action of heavy loads, greater than the swelling pressure, the soil undergoes consolidation. The rate of consolidation depends on the applied load, coefficient of permeability, thickness, and compressibility of the soil. The objective of this thesis is, therefore, mainly intended to investigate the relationship between swelling & consolidation behavior of expansive soils of Galan Town using one-dimensional consolidation theory of Terzaghi. To attain the purpose of this research, representative disturbed & undisturbed samples of expansive soil were collected from different locations of Galan town & a series of swellconsolidation tests were carried out in the laboratory. According to the test result obtained from Index property tests, the expansive soil of Galan Town, according to USCS is classified as Inorganic Clays soil of high plasticity, CH, & A-7-5 according AASHTO soil classification. The value of compression index Cc obtained from expansive soils of Galan Town, ranges from 0.24-0.34 & the value of coefficient of consolidation Cv ranges from 0.32-0.42 m2/year, while initial dry density & initial moisture content range of 1.17- 1.37 g/cm3 & 30.6-50.1% respectively during the sample collection In the course of this research, it has been found that swelling potential of expansive soils decrease with increase in initial moisture content for constant dry density. On the other had the percent swell & swelling pressure increase with increasing initial dry density increases. Maximum swelling pressure is obtained from the samples prepared with optimum moisture content & maximum dry density. The value of compression index Cc of sample with high swelling potential (high degree of disturbance) is greater as compared to samples with low swelling potential. Increase in moisture content decreases the amount & rate of both swell and consolidation. Therefore, the consolidation characteristic of expansive soil is not inherent property of the soil mass because, swelling is also additional factor that can influence consolidation characteristics expansive soil.
Assessment of Damages Caused by Expansive Soil on Buildings Constructed in Bahir Dar
(Addis Ababa University, 2015-12) Solomon, Tibebu; Haile, Messele (PhD)
In this study it has been tried to assess the extent of damages caused by expansive soil on buildings constructed in Bahir Dar. Seventy Eight buildings were randomly selected from 20 different expansive soil locations. The assessment showed that out of those 78 buildings 68(87%) of them are adversely affected. In most buildings more than one building components are damaged. The damage has been analyzed and interpreted systematically with respect to type of foundation, wall, floor, pavement, door, window and fence. The extent of damage is very high on pavements and decreases when we proceed to walls, floors and foundation in their respective orders. The study showed that the main cause of failure is fluctuation of ground water table. In addition to this poor surface drainage, presence of tress and vegetation close to buildings, damaged utility lines and improper design also have great contributions. Based on the causes of failures and other factors attempt was made to propose remedial measures for already damaged buildings constructed in expansive soil locations of the study area. In addition to this suitable foundation types and construction details have been also proposed for new buildings to be constructed in these areas.
Assessment of Damages Caused by Expansive Soil on Roads Constructed in Addis Ababa
(Addis Ababa University, 2022) Desalegn, Workie; Henok, Fikre (PhD)
Roads are one of the basic infrastructures and serve as means of a communication system for any country. The investment budgeted and the cost for original construction and repair of roads of our country is relatively high. Most of the time road lines constructed in our country failed early before functioning the design life. This is because of various problems arising from different causes. Among these roads which are failing before serving its design life is the Addis Ababa Roads. The main reason is that large areas of these roads are constructed on problematic expansive soils. This is due to improper construction and operation of the road. It is well known that Addis Ababa is a populated and investment area as it is the capital city of Ethiopia. As a result, the roads in Addis Ababa serve or carry the highest daily traffic in the country. These roads were constructed and opened to traffic in different years accordingly. The design pavement life was estimated at 15 and above years, however; pavement structure failures have been observed since construction time, within the first few years after opening to traffic. From the end of construction to date, the Addis Ababa roads are repeatedly under periodic maintenance. Considerable resources were spent during this period on periodic maintenance, but without solving the basic problem. This maintenance is not working as each maintained section is failing within a short period, hence, it needs to investigate the root causes of the failure to come up with an appropriate solution. This paper tries to present some issues of geotechnical cases for roads built on expansive soils. Some case study sites, representatives knew problem-areas in Addis Ababa were carefully selected for geotechnical site investigation. The field exploration consisted of detailed observation and measurement of damaged roads. These road damages have been identified and characterized based on the theoretical aspect of soil property and its effect on construction. This work was also have been used any secondary data concerning the study area as a baseline and it was helped as an input. Field investigations which include visual condition survey, DCP test, Benkelman Deflection measurement, and other methods were conducted to investigate causes of failure. Finally, based on the investigation, all causes of road failure are identified. Based on the identified damage types and their causes, maintenance and rehabilitation mechanism or techniques are recommended and suggested.
Assessment of Road Pavement Failure Along Addis Ababa-Modjo Trunk Road
(Addis Ababa University, 2015-03) Abate, Asnake; Tadesse, Samuel (PhD)
Most of the roads constructed in Ethiopia fail prematurely before serving the design life due to various causes arising from many factors. One of these roads failed before reaching design life time is the Addis Ababa-Modjo Trunk Road. The Addis Ababa-Modjo road is approximately 50 km trunk road and very crucial for the country’s transportation and tourism sector as it is the main import export corridor to and from the capital, Addis Ababa. The road carries the highest daily traffic in the country. This road was constructed and opened to traffic in the year 2000. The design pavement life was estimated 15 years, however; pavement structure failure have been manifested since 2005, within the first 5 years after opening to traffic. From end of 2007 to date the Addis -Modjo trunk road is repeatedly under periodic maintenance. Considerable resources have been spent during this period for periodic maintenance but without solving the basic problem. This maintenance is not working as each maintained section is failing with in short period, hence, it needs finding the root causes of the failure to come up with appropriate solution. Field and laboratory investigations which include visual condition survey, Benkelman Deflection measurement, test pitting and pavement layer profiling, materials sampling and testing have been conducted in order to investigate causes of failure moreover, the past traffic data was collected and analysed. Finally based on the investigation, expansive subgrade soil, side drain problem, workmanship problems, use of substandard materials are found to contribute for the pavement failure. However, it is noted that the traffic load take the highest share for the cause of pavement failure. Proper treatment of expansive subgrade soil, use of quality construction materials, proper maintenance design based on the forecasted traffic are recommended as mitigation measures. Key Words: Pavement Failure, Condition Survey, Traffic Loading, Maintenance, Benkelman Beam, Deflection.
Assessment of “Piled Raft Foundation” for HighRise Buildings Under Vertical Load in Addis Ababa: The case of Nib, Zemen, and United Bank Headquarter Buildings
(Addis Ababa University, 2018-06) Mahidre, Mamo; Henok, Fikire (PhD)
Piled Raft foundation is a newly emerged foundation system. Different researchers are working on it till now. The system is mainly used to respond to weak foundation materials. The intent of this study is, to assess the piled-raft foundations of high-rise buildings under vertical load. These foundations are designed by local engineers to respond to high-rise building foundation requirement. The study is conducted using finite element method software package – ABAQUS. The numbers of projects considered in this study are three. They have similar nature and are under construction. The designers use similar pile spacing for all projects and it is the only variable parameter in this study. The foundations are modeled with pile spacing of 3D (designers spacing) and 6D (two times designers spacing). The site's geology is predominantly rocky but in different weathered condition. The assessment result shows maximum and differential settlement of the foundations are very insignificant and angular distortion is within permissible limit. Almost all the vertical load is taken by the pile and the load shared by the raft is very insignificant.
Bamboo as Temporary Soil Reinforcement
(Addis Ababa University, 2015-10) Goshime, Addishiwot(Dr); Tadesse, Samuel (Dr)
Now-a-days, the high cost and lack of reinforcing steel in many parts of the world has directed to increasing interest in the possible use of other locally accessible materials for the construction. For this reason the main objective of this research is to undertake the use of bamboo as temporary soil reinforcement which is inexpensive and local available material in Ethiopia. For the thesis study Shimal bamboo (Oxytenanthera abyssinica) was used as reinforcement. This bamboo is found in Benishangul–Gumuz Regional State and it is covered the area of 440, 000 hectares. The primary purpose of reinforcing the soil is to improve stability, to increase modulus of rigidity and to increase the strength of lateritic soil which is found in Assosa region. The tests were carried out to find the use of bamboo as temporary soil reinforcement material. Accordingly ASTM, several laboratory tests were conducted. Atterberg limits (PI, LL, and PL), washed sieve analysis, hydrometer analysis and specific gravity on the air dried soil; standard compaction tests and unconfined compression tests on the molded soil –bamboo sample were conducted. The soil specimens were molded in cylindrical form of 38mm diameter and 76mm height while the bamboo specimens were trimmed in to square plates of 24mm size and 3mm thickness. The trial soil specimens are: soil specimen without bamboo specimen (0 bamboo), soil specimen with one bamboo specimen in the center (1 bamboo), soil specimen with one bamboo specimen on top and one at the bottom (2 bamboos) and soil specimen with one bamboo specimen on top, center and bottom (3 bamboos). A lateritic soil classified as A-7-5 under AASHTO soil classification system was reinforced with 0, 1, 2 and 3 bamboo specimens at laboratory trial level to evaluate its unconfined compressive strength (UCS) and modulus of rigidity. From the bamboo laboratory test result, the dry density of the molded soil specimen decreased from 1.41g/cm3 at 0 bamboo specimen to 1.35g/cm3 at 3 bamboo specimens, the UCS Bamboo as Temporary Soil Reinforcement 2015 AAU/AAiT School of Civil & Environmental Engineering/Geotechnical Engineering Page iii increased from 278.96kN/m2 at 0 bamboo specimen to 381.71kN/m2 at 3 bamboo specimens. Also, for each of the four percentage strains (0.01, 0.02, 0.03 and 0.04%) considered, the modulus of rigidity increased with bamboo specimens. Key Words: - Bamboo; Modulus of rigidity; Optimum moisture content; Friction
Bio-Enzyme Stabilization of Red Clay Soil
(Addis Ababa University, 2021-04) Dagnachew, Seifu; Mesele, Haile (PhD)
Enzyme based liquid soil stabilizers have emerged as an alternative soil stabilization technique and are being introduced to the road construction industry, with an objective to improve the geotechnical properties of soils and ultimately reduce the overall cost of the projects. However, evidence to support the effectiveness of these products as stabilizer is based on manufacturer’s claims in their marketing brochures and manuals. Thus there is a need for an independent assessment of these products. Accordingly, this study is performed to evaluate the effect of TerraZyme which is an Enzyme based liquid stabilizer in improving the engineering properties of a red clay soil. Soil samples were collected from five different location in the northern part of Addis Ababa, and different laboratory tests were conducted on the soil samples with and without the application of TerraZyme. These tests include Particle Size Distribution, Plasticity Index, CBR and Unconfined Compressive Strength tests. The result obtained shows a slight increment in the UCS and CBR tests of the soil but the improvement is very small to warrant a large scale application of TerraZyme for red clay soil. Therefore, the type of soils in which the TerraZyme application can produce an optimal result should be investigated before applying TerraZyme on a large scale projects.
Bored Soldier Pile Analysis and Design Practice in Addis Ababa (Case of 4B+G+6 Podium and 15 floors Assem Building)
(Addis Ababa University, 2022-03) Roza, Tsegaye; Tezera, Firew (PhD); Leamlak, Minwuyelet (Mr.) Co-Advisor
The purpose of this research is to show the benefit of the Finite Element Method over the Conventional Analysis Method for deep excavation design. This research is conducted on the Assem Building excavation, which has a 4B+G+6 podium and 15 stories and is located in Addis Ababa, Ethiopia, and is surrounded by busy roads and buildings. Following a comprehensive assessment of the literature on the analysis and design of excavation support walls, specifically anchored soldier pile walls, FEA and conventional analytic methods are used to model the excavation of the Assem Building. In the conventional analysis approach, the Assem Building's excavation support walls were analyzed and designed using the DeepEX software program and the GEO5 "Sheeting Check" software tool. Similarly, the FEA method uses the Plaxis 2D software program. Similar model sizes and soil and structural element parameters are used throughout all software programs. The following result was achieved by analyzing the Assem Building excavation. According to the FEA and optimized FEA results, the bending moments along the pile length are 40 % and 36 % lower, respectively, than those found using conventional analysis methods. Similarly, shear force calculated using FEA and optimized FEA are 41 % and 44 % lower, respectively, than those calculated using conventional analysis. The conventional method makes considerable assumptions about the solutions, but the FEA method makes no such assumptions and treats the problem as it is. As a result, the FEM result is lower than that of the conventional method. Because of the lower results, the FEA approach saves 9% to 11 % of the cost of the conventional analysis method. The optimized FEA also results in a cost reduction of 14 to 15%.
Channel Stabilty Analysis -the Case of Borkena River (Ethiopia)
(Addis Ababa University, 2008-03) Mengesha, Fantaw; Channe, Bayou
Rivers dynamically respond to changes in the discharge and sediment supply of catchments. A change of land use and other natural factors in catchments result in changes on sediment supply and discharge. And this process of change of river geomorphology seeking for its equilibrium may affect people and property especially in urban areas located adjacent to rivers. The Kombolcha town, situated on flat land plains in the middle course of the Borkena River is facing a danger of flooding and destruction of properties due to the instability of the Borkena and Berberie River reaches crossing the town. To prevent the loss of lands and properties resulting from the changes in the characteristics of those river reaches, stabilization measures must be employed. For proper design and implementation of any stabilization measures, analysis on stability of these channel reaches must be carried out. So this thesis deals with analysis of the stability of the channel reaches by evaluating their capacity and stability in response to discharge and sediments that are supplied from the catchments. Field investigation and surveying to collect data for channel cross sections, bed & bank material, and the vegetation covers is carried out. Gradations of bed and bank materials are determined in laboratory using sieve analysis. Design discharges of different return periods and quasi unsteady flow data are analyzed from measured maximum daily instantaneous discharge data. Using such flow and existing field data as input, HEC-RAS 4.0 beta version is used for simulation of flow and mobile bed sediment transport Based on the model results which are analyzed using the Meyer Peter Muller and Yang’s sediment transport formula, deposition is observed in almost all of the stations of the Borkena River. And there is deposition at some of the down stream stations in the tributary reach and degradation in the rest. It is also analyzed that the material on the banks is less resistance to the minimum shear induced by the flow, besides much of the stations in the tributary reach are geotechnically unstable. Over flooding still is the problem on upper and lower reaches of Borkena which is resulted from the complex processes of aggradational problems. And stabilization measures are proposed and should be implemented with further engineering, economical and hydraulic analysis for effective and sustainable stabilization of the rivers.
Comparative Assessment of Excavation Supporting Systems in Addis Ababa
(Addis Ababa University, 2024-01) Kidist Afewerk; Henok Fikre (PhD)
Addis Ababa, Ethiopia's growing capital city, has witnessed rapid urban development, necessitating the construction of towering structures. As the need for deep excavation arises, Engineers face the challenge of maintaining stability while digging into the earth. This necessitates using temporary earth retaining structures known as excavation supports or shoring to prevent soil collapse and ensure precise excavation. Various methods are available for excavation support, including soldier beams and lagging, sheet piling, bored pile walls, soil nailing walls, and slurry (diaphragm walls). In Addis Ababa, specialized firms dedicated to foundations construct excavation support systems. The first foundation specialist company in the country, BAUER MIDROC Foundation Specialist Plc., was established on June 12, 1998. Addis Ababa has varying soil types, but the protection system used is uniform, causing specific problems such as costly temporary shoring systems and time-consuming installation. Local companies compete by compromising safety, leading to the collapse of excavation support systems with major damage, including loss of human life, additionally, machinery has a short lifespan due to difficult strata placement. The study aims to access different shoring methods in Addis Ababa and compare conventional contiguous pile walls with soil-nailing walls for various sites and soil conditions that are practical, reliable, appropriate, and adaptable solutions for local firms. To achieve this, first gather information about three different sites, including soil strength, excavation depths, surcharge load, and available space for the supporting system structure. Numerical methods such as finite element analysis and limit equilibrium analysis will be used to create models of the deep excavation stabilizing methods for each site and method. After that compare two methods of construction costs and construction period based on the obtained designs. In conclusion, this research aims to provide valuable insights into the most effective and suitable excavation supporting systems for specific site conditions and soil types in Addis Ababa. The particular approach employed in this study, along with considering various factors, ensures that the findings are reliable and applicable to the context at hand. The results of this study can be valuable for contractors and Engineers in selecting the appropriate excavation supporting system in Addis Ababa.

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