Geotechnical Engineering
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Item Characterization of Addis Ababa Expansive Soil Using Unsaturated Soil Properties(Addis Ababa University, 2024-04) Atnatewos Minale; Tezera Firew (PhD)Proper characterization of expansive soils is critical in geotechnical engineering practice for proper design. However, a limited researches were done on unsaturated expansive soil properties in Addis Ababa. The availability of soil suction profiles from in situ and laboratory measurements is currently limited. This research aims to enhance geotechnical site assessments in Addis Ababa’s expansive soil regions through combined laboratory testing and long-term field monitoring of unsaturated soil properties. To properly characterize the unsaturated properties of expansive soil laboratory pressure plate analyses were performed on twelve undisturbed soil samples to develop soil-water characteristic curves (SWCC) with two categories four of them from under roadway and eight from excavations for a building purpose with a varying depth and locations coupling with shrinkage curves (SC). The SWCCs were determined using a pressure plate apparatus with a suction range of 0 to 1300kPa. The laboratory-measured data points were then curve-fitted by using the Fredlund and Xing (1994) model. The SC was also determined to evaluate the change in volume of the different soil samples. Experimental results reveal Air Entry Value acquired through consideration of volume change with Degree of Saturation Soil-Water Characteristic Curve (S-SWCC) is higher in magnitude than gravimetric water content soil water characteristic curve (w-SWCC) and a volume change of 74.15-79.8 for soil samples from under roadway and 83.1% - 98.1% for soil samples sampled from excavations for building construction is quantified through void ratio characteristic curves. Concurrent field monitoring was conducted to capture seasonal matric suction profiles in Addis Ababa using a digital tensiometer and Diviner 2000 probes to directly measure matric suction profiles and volumetric water content. This study implemented direct long-term monitoring of matric suction in situ at multiple depths (140cm,160cm, and 190cm) using digital tensiometer equipment. And coupled with volumetric water content measurements gathered using Diviner 2000 sensors. Integrating the tensiometer data and diviner 2000 from June to October, the soil suction profile with depth and time is shown. Seasonal matric suction measurements from the field showed that temporal pattern of fluctuation with depth. The magnitude of matric suction values ranges from 23 to 83kPa based on the depth of the soil for a volumetric water content ranging from 12-53%. Matric suction profile with depth is found increasing with a magnitude of difference varying based on the soils volumetric water content for the depth of investigation.Item The Performance of a Recently Developed Two-Parameter Foundation Model for the Analysis of Raft Foundation(Addis Ababa University, 2025-06) Frehiwot Belay; Asrat Worku (Prof.)Different viewpoints on modeling the Soil-Structure interaction (SSI) in mat foundation design exist in engineering practice. Some believe that modeling the SSI using a few mechanical elements during design is sufficient, while others contend that modeling the soil as a continuum model is necessary to produce an adequate analysis. Commonly, the analysis and design of mat foundations is done by performing static analysis of a plate resting on vertically uncoupled Winkler springs. Despite being a somewhat simplified idealization of reality and the emergence of more accurate techniques, the Winkler spring methodology continues to be the state-of-the-practice because it is simple to implement in most commercial structural analysis computer programs. This and related shortcomings have meanwhile been addressed by a number of improved models including Worku's two-parameter subgrade model (2014). Worku’s model is a mechanical equivalent of an originally elastic continuum idealization of the soil under the foundation, whereby all components of the continuum deformation and the stress and strain tensors are retained. This is unlike a number of previous similar attempts by other authors, who proposed simplified versions of such a continuum representation. The implementation of this analytically rigorous model into applications such as beams and plates on elastic foundations and laterally loaded plates has been under investigation showing promising results. This thesis deals with a comparative study of the performance of the model to rectangular raft foundations against existing methods of analysis. To this effect, a recently adjusted version of the model under an on-going PhD research is employed. A finite element algorithm developed under this project and written in MATLAB to solve the resulting partial differential equation of the plate along with a calibration chart for different loading conditions was used and compared with a rigorous continuum based finite element model of the plate-soil system (cFEM). The findings show that the model adequately represents the behavior of rectangular plates on elastic foundations showing remarkable agreement with the cFEM outputs.Item Dynamic Soil Characteristics of Selected Sites in Bole Sub-City of Addis Ababa(Addis Ababa University, 2025-05) Yeabsira Bekele; Tensay Gebremedhin (PhD)Addis Ababa which is situated on the margins of ethiopian rift valley system is positioned in seismic zone 3 according to ES EN 2015. The city has a moderate seismicity. This study investigates the dynamic properties of soils taken from selected test pits in bole Subcity of Addis Ababa city at 2.5m sampling depth. To assess the area's capacity to resist dynamic loads from potential earthquakes, both index and dynamic properties of the soils were evaluated. Index property tests including atterberg limits, particle size analysis, free swell, and specific gravity revealed a wide range of test results. Based on USCS soil classification system the soils samples were identified primarily as plastic clay and clayey sand . Dynamic behavior was further examined using cyclic simple shear tests at varying strain amplitudes (0.01% to 5%) and axial stresses (100 kPa to 400 kPa). The stress strain responses were recorded, and the shear modulus and damping ratio were obtained for each soil sample. The findings were compared with local and international studies, contributing valuable data for seismic hazard assessment and earthquake-resilient design in the region.Item Prediction Of CBR Value of the Subgrade Using Dynamic Cone Penetration Test (A Case Study on Beredimtu – Imi Road Project)(Addis Ababa University, 2025-04) Samson Molla; Samuel Tadesse (PhD)The significant advantage of the Dynamic Cone Penetration (DCP) test is that it is a low cost, robust apparatus that is quick and simple to use. With the DCP testing, very little damage is made to the pavement being tested (effectively non-destructive) whereas very useful information is obtained. Another interesting advantage of the test is that the pavement is tested in the condition at which it performs. The simplicity of the test allows repeated testing to minimize errors and also to account for temporal effects. On the other hand, California Bearing Ratio (CBR) is a very popular in the construction industry especially, in road construction as a soil support value of the pavement. However, CBR cannot be easily determined in the field. This initiated the need to investigate the relationship CBR value has with other field tests like DCP. As part of this study, primary field and laboratory subgrade tests for the locally available subgrade soil of the case project, Beredimtu – Imi – Gode road project, were conducted. Using the test results, the relationship between field and laboratory subgrade soil strength tests were in-depth investigated. Based on this laboratory and field test results, CBR values were correlated with DCPI values using a simple regression coming up with an R2 of 0.958 and low standard error of estimate. On the other hand, the CBR has been correlated with the DCPI and the bulk density using a multiple regression technique with the equation having and R2 of 0.854. Hence, the equation obtained with and R2 of 0.958 is used for validation puepose.Item Site specific Ground Response Analysis at South - Western part of Addis Ababa(Addis Ababa University, 2024-12) Birkit Solomon; Tensay Gebremedhin (PhD)Ethiopia's capital, Addis Ababa, is situated near the edge of the Ethiopian Rift System, an area with moderate seismic activity. The city is vulnerable to earthquakes due to its geographic location. Because the characteristics of soil affect seismic wave propagation, amplification and attenuation, studying site effect is crucial for earthquake investigations in a particular location. For this purpose, a two-dimensional ground response analysis is performed using soil data from geotechnical investigation reports and multi-channel analysis of surface waves (MASW) to characterize the soil profile of selected sites at five sub cities that are found on the South – Western part of Addis Ababa and to determine how these locations affected the input ground motions. Considering the local geology and tectonic circumstances, the input ground motions are selected from the PEER ground motion database. Ground response analysis is conducted using the input soil data and five ground motions at the ground surface in the PLAXIS 2D software. And based on the results and shape file of the study area, Seismic micro zonation map is produced. The results of the analyses indicate that the selected sites have a significant potential for amplifying ground motions. This amplification is notably higher than current local code specified predictions but near to NEHRP provisions. Therefore, it is recommended to revise the local code spectra and conduct a detailed investigation and mapping of the rest six sub cities of Addis Ababa to ensure accurate seismic risk assessment and improve safety measures.Item Effect of Dynamic Soil-Structure Interaction on Buildings in Selected Sites of Addis Ababa(Addis Ababa University, 2025-01) Rediet Lemma; Asrat Worku (Prof.)Currently, structural engineers typically design structures as fixed-base systems, neglecting soil-structure interaction (SSI). This practice is primarily due to the complexities associated with soil modeling and the absence of specific procedures for incorporating SSI effects in many seismic design codes including the Ethiopian code. Both the European and Ethiopian building codes recommend dynamic SSI effects for slender structures or those with significant second-order (P-Δ) effects. However, they mandate the inclusion of SSI in design without providing explicit guidelines for its calculation. Structures founded on piles or massive foundations, such as offshore caissons, silos, and bridge piers, should account for SSI effects in their design (ES EN 1998-5:2015; ES EN 1998-5:2015). In contrast to the European and Ethiopian building codes, international codes and standards, such as ASCE/SEI 7-10 (2010), ASCE/SEI 7-16 (2017), and ASCE/SEI 41-17 (2017), provide procedures for incorporating SSI into structural design. This research delves into various studies and evidence, emphasizing the need for a nuanced understanding of SSI effects on building structures. Additionally, it explores the main approaches employed to evaluate seismic SSI problems, focusing on commonly used modeling techniques and computational methods. Notably, the thesis adopts the code approach outlined by NIST GCR 12-917-21 (2012) based on Pais and Kausel (1988), FEMA P-2082-1 (2020) and ASCE/SEI 7-16 (2017) to address and analyze SSI-related challenges in seismic analysis of buildings. To ground the study in real-world scenarios, five specific sites in Addis Ababa were selected based on recent ground response analyses conducted by Getu (2023). Additionally, one idealized softer site was included. The selected sites from Getu (2023) correspond to two ground types, C and D, according to ASCE/SEI 7-16 (2017). The inclusion of the idealized soil condition was intended to more clearly observe soil flexibility, which is assumed to correspond to ground type E according to ASCE/SEI 7-16 (2017). Five earthquake motions selected from the PEER ground motion database were matched to these ground types, and four building models, ranging from G+5 to G+30, were assumed. The analysis was conducted using ETABS 21.1.0 software. The common perspective on Soil structure interaction (SSI) has long regarded it as a beneficial factor in structural response. However, contemporary research and insights gleaned from past seismic events have revealed instances where consideration of SSI can exhibit detrimental effects under specific conditions. In this study, it is observed that some structures with flexible base models show a smaller response compared to their fixed-base counterparts. However, in certain cases, a significant increase in response is observed. This increase is dependent on the predominant period of the earthquake motions and the fundamental period of the structure. Within the scope of the study conducted, as the number of stories increases, the SSI influence increases, particularly for storey displacement, storey drift ratio, and storey overturning moment. Additionally, SSI also leads to reduced base shear for shorter building models in most earthquake motions.Item Geotechnical Investigation of some Failed Sections along Omo River-Tercha Road Project(Addis Ababa University, 2024-04) Biniam Yihun; Tensay Gebremedhin (PhD)This thesis investigates the geotechnical failures within the Omo River-Tercha Road Project, specifically focused on unanticipated premature failures emerged shortly after opening the road for traffic. The study initiated by examining relevant project documents and conducting comprehensive on-site surveys to identify and record signs of geotechnical failures along the project road. Among these, five major geotechnical failures were identified as significant for further detailed investigation: saturation of recently placed pavement materials and surface pumping, erosion on the surface of roadway cut slopes, depression and several cracks in newly placed pavement, failure of roadway cut slopes and failure of roadway side fill slopes. After conducting extensive assessments of each failure, which involved a thorough analysis of available project design and construction data, a detailed on-site investigation to detect signs of failure, soil sampling for laboratory testing to examine soil properties and modeling of road cross-sections at locations of slope failure to identify slip surfaces and calculate factors of safety. As a result, the study revealed significant factors contributing to these premature failures, including inadequate subsurface drainage, removal of vegetation covers, problematic subgrade soil, steep geometry of cut and fill slopes, challenges associated with Design-Build contracts and limited engagement of geotechnical engineers. In response to these findings, the thesis has proposed remedial measures to this newly completed road project. These measures include the establishment of longitudinal interceptor drains for subsurface drainage, re-vegetation with the use of soil erosion blankets, installation of vertical moisture barriers to encapsulate problematic soil, flattening of slopes and integration of geo-grids into the construction of fill slopes within confined spaces. Prompt action is recommended to implement these measures, preventing further damage, minimizing maintenance costs and ensuring infrastructure longevity. The findings provide valuable insights for future road projects, emphasizing proactive geotechnical considerations in design, construction and maintenance.Item Numerical Analysis of Embankment Dams with and without Geosynthetic Reinforcements (Case Study On Kalid-Dijo Zoned Embankment Dam)(2024-06) Gemechis Ayana; Tensay Gebremedhin (PhD)Soil reinforcement technology is now well-established technique for geotechnical applications in most parts of the world. This thesis was intended to numerically investigate the benefits of soil reinforcement techniques, in static and dynamic stability of zoned embankment dams in Ethiopia. The dam section designed by ECDSWCo has been considered for the case study. The detail static and dynamic analyses were conducted for the dam without geosynthetic reinforcements initially and then the slopes of this dam was considered to be reinforced with horizontal layers of geosynthetic reinforcements (geotextiles) by replacing the rock fill zone with granular shell fill for cost minimization. The analysis was carried out by using state of the art software Geo-Slope International Ltd, finite element and limit equilibrium based packages, based on analysis type. Different analysis alternatives were conducted for the reinforced dam by varying the spacing of the reinforcement layers to optimize safety and economy. Hence, this study demonstrated that reinforcing embankment dam slopes with horizontal layers of geosynthetic reinforcements improves the embankment dam's safety and economy. By using only six layers of geosynthetic reinforcements, arranged in 4m c/c spacing for both upstream and downstream slopes, the static stability factor of safety was improved by an average value of 34.5%, the amplification value at the dam crest was reduced by about 59%, vertical crest displacement was reduced by about 24% and approximately 25% of the embankment fill construction cost was saved from the dam without geosynthetic reinforcements.Item Landslide Assessment, Susceptibility Analysis and Recommendation of Remedial Measures for Jimma-Chida Road Segment, South-West Ethiopia(Addis Ababa University, 2024-05) Lemenew Minale; Tezera Firew (PhD)In Ethiopia, landslides, mostly demonstrated as rock fall, earth slide, debris, and mudflow, are prevalent in the central, south-southwest, and north-northwest highlands, especially after intense rainy season. Jimma-Chida road section which is studied in this paper is located in southern highlands and lies in Gibe and Gojeb River Basins where landslide incidence occurred frequently. This work studied the active landslide areas along Jimma-Chida road by assessing their features, failure mechanism and extent of the landslides. Landslide susceptibility map is produced by weighting factors that contribute to the landslide using Analytical Hierarchy Process(AHP) method and integrating it with the existing landslide inventory data. For this purpose, key factors (lithology, elevation, rainfall, slope, slope aspect, land use/ cover, distance to stream, distance to road and curvature) are considered and weighted after dividing into sub-factors using AHP. Then the causative factor layers are overlaid using weighted overlay technique in ArcGIS environment to produce the landslide susceptibility map. From the assessment of the existing landslide it is revealed that slope angle (90-140), slope aspect(Northwest), elevation (2388-2732 m), curvature(flat), lithology (residual soil of upper basalt flow), distance to stream (50 m), distance to road (50 m), land use/cover (crops) and rainfall (1600-1675 mm) have higher contribution for the occurrence of the active landslide. Based on AHP for landslide susceptibility map, distance to the stream, distance to the road and rainfall are the most contributing factors with weight 0.203,0.197 and 0.199, respectively. The other influential factor is lithology with weight of 0.167, followed by slope angle, aspect, elevation, curvature, land use/cover with the weight 0.073,0.023,0.023 and 0.059, respectively. The landslide susceptibility map concludes that Jimma-Chida road section is classified as low (32.23%), moderate (62.87%), high (4.89%), and very low and very high susceptibility zones are covered a very small and localized areas. Finally, modification of the slope geometry, provision of both surface and sub-surface drainage, provision of retaining structure and internal reinforcement of slope are recommended as a preliminary remedial measure for the area affected by landslide.Item Improving The Characteristic of Collapsible Soil Using Pumice(Addis Ababa University, 2022) Yehamleshet Bekele; Samuel Tadesse (PhD)Collapsible soils, which are sometimes referred to as metastable soils, are unsaturated soils that undergo a large change in volume upon saturation with or without loading which pose problem to civil engineering structure. Many researches have been done and variety of methods and techniques have been proposed for improving the engineering property of this soil to make suitable for civil engineering structure built on it. Some techniques used for improving collapsible soils are partial excavation and replacement with compacted fill, dynamic compaction and chemical stabilization. Alternatively, use of other local abundant available pumice material as a means improving is one method which reduce damages on structure. This study was undertaken on collapsible soil sample taken from Ziway-Adamitulu Woreda. The change in engineering properties of this soil investigated with addition of increasing percentage of pumice. Pumice is the most locally abundant available material around the aforementioned area. The preliminary investigation of the soil to be improved initially characterized and classified based on indicative tests and found to be A-4 according to AASHTO and SM class of soil according to USCS systems. Compaction, direct shear, CBR and collapsible potential tests were used to evaluate engineering properties the improved soil. Field density tests also conducted to determine the in-situ densities of the soil. Analysis of the results shows that the collapse index of natural and compacted untreated soil 6.720% with moderate severe disorder soil at bulk and 2.235% with moderate disorder soil at OMC respectively. Treating this soil with pumice reduce collapsible index from moderate disorder soil (2.235%) to slight disorder soil (0.329) % at optimum content of 25 % pumice according to ASTM D5333. Similarly, MDD decrease and CBR, Shear strength and OMC values increased as pumice content is increased. Curing has significant effect on the geotechnical properties of pumice-stabilized soil. Therefore, this experimental result contributes in solving the problems of soil collapse by treating to enhance its resistance.Item 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.Item Correlating CBR values with basic soil parameters (by using Neuroxl Predictor)(Addis Ababa University, 2024-01) Airmeyas Aychew; Henok Fikre (PhD)The California bearing ratio (CBR) is an essential design parameter for soils and an indirect measure of soil strength. This is broadly used for the design of sub-grade, sub-base and base course materials for road, railway, and airfield projects. It is also used as a direct relationship to determine the response of the base or sub-base soil. This research studies the relationship between CBR values and other parameters of soil properties, although the samples include coarse and fine-grained soils, using advanced neural network programs to help us obtain an accurate predicted value. Most of the previous studies were conducted on fine-grained soil types and also used conventional multiple linear regression analysis methods. To satisfy the objective of this study, one hundred and ninety-eight soil sample test results were collected. I participated as a material engineer in the testing and reporting process. Laboratory testing was performed in accordance with AASHTO standard test methods. Modified compaction, soak three-point modified CBR, wet sieve analysis, and Atterberg limit tests were performed on a total of one hundred and ninety-eight soil samples. Statistical analyses were performed to validate the new model using 30 percent of the total sample size. Two types of analysis programs—Microsoft Excel software (ANOVA) for multiple non-linear regression relationships and the advanced NeuroXL predictive neural network program—were used to predict CBR values. Independent soil property parameters were liquid limit, plastic limit, plastic index, amount of particle size less than 0.075 mm, amount of particle size less than 0.425 mm, amount of particle size less than 2.00 mm, amount of particle size less than 4.75 mm, optimum moisture content, and maximum dry density. This study provided two alternative models. The first alternative model included compaction test parameters (OMC and MDD), particle size distribution parameters (4.75 mm PP, 2 mm PP, 0.425 mm PP, and 0.075 mm PP), and plasticity parameters (LL, PL, and PI). They were taken as independent parameters. The second alternative model excludes the compaction test parameters (OMC and MDD) as independent parameters when compared to the alternative one. This study used two alternative analysis techniques: the first group of analysis techniques developed model equations for each classified data set (sub-grade, sub-base, and sub-base), and the second technique developed model equations for the unclassified data set group. The predicted CBR values of both the NeuroXL prediction and multiple nonlinear ANOVA regression models were compared with the actual CBR values, which confirmed that there was an acceptable difference between the actual and predicted CBR values between both analysis methods.Item Prediction of Soil Water Characteristic Curve Based on GSD and PI for Red Clay and Expansive Soils Found in Addis Ababa(Addis Ababa University, 2013-09) Nuru Ismail; Hadush Seged (PhD)Many researchers have done researches on unsaturated soil mechanics worldwide to bring the unsaturated soil mechanics in to practices. Among those researches some of them focused on simplifying the complex and expensive testing mechanism by developing models which can be used to predict the unsaturated soil parameters from basic soil prosperities such as Grain Size Distribution (GSD) and Plasticity Index (PI) along with the saturated shear strength parameters. Soil water characteristic curve (SWCC) was proved to have good relationship with the unsaturated soil parameters. In this study an attempt was made to check whether those developed models would work for expansive and red clay soils found in Addis Ababa. Using the model developed by Fredlund and Xing (1994) along with the correlation equation given by Perera et.al (2005), family of SWCC for soils found in Addis Ababa has been plotted. It was observed that the family of SWCC plotted was out of the widely referenced family of curves developed by Zapata et.al (2000) to some extent. Even though the family of curves seems to be out of the range provided by Zapata et.al (2000), the model gave good prediction for the unsaturated shear strength parameter Φb. The percentage error between the measured values of unsaturated shear strength parameter Φb in previous researches of Habtom (2010) and Getaneh (2010) with predicted unsaturated shear strength parameter Φb in this study was compared. For red clay samples the percentage error lie in the range 2.07 to 6.37% for suction ranges of 36.67 to 52.9 kPa and at lower suctions of 16.75 and 21.5 kPa the percentage error ranges from 11.42 to 25.39% . For expansive soil samples for suction of 23.1 and 32.9 kPa, the percentage error is in the range from 3.86 to 6.13%. For suction values of 14.5 and 52 kPa the range of error is about 9.45 to 13.40% and for suctions of 38.8 and 48.6 kPa the error lies between 18.94 and 38.84%.Item Developing Correlation Between Index properties and California Bearing Ratio, CBR of Soils: A Case Study on Guliso Cheliya Dilla Kondala Begi Road Project, Lot 2(Addis Ababa University, 2023-07) Gudata Mokonon; Henok Fikre (PhD)Soil properties are specific to a region and alter greatly from place to place based on climatic and geographic conditions. Geotechnical engineers often attempt to develop empirical methods specific to particular regions and soil types. However, empirical equations are more consistent for soil types where the correlation is developed. Therefore, it is extremely important to develop a correlation between CBR and subsoil index properties specific to different soil types. This project comprises developing the relationship between CBR values and soil index properties specific to the Guliso Cheliya Dilla Kandalama Begi road project. When finding the correlations, both simple and multiple regression analyzes were considered. Accordingly, one hundred and ten secondary data sets were collected from Best Consulting engineers, consulting firm, to attain the intended correlations. Using SPSS, the CBR correlation is constructed as a function of Atterberg limits, percentage grain size, and moisture-density relationship parameters. After evaluating developed correlation, it was found that CBR values and soil index properties are well correlated and this is advantageous for the preliminary detection of the geotechnical characteristics of the soil in the investigation area. Finally, a reliable correlation is derived from correlation work with a coefficient of determination of 0.691 using multiple linear regression analysis.Item Lateral Static and Dynamic Response of Single Piles in Non-Homogenous Soils using a Standalone Two-Parameter Foundation Model(Addis Ababa University, 2023-03) Mathewos Endeshaw; Asrat Worku (PhD)In the design and analysis of structures supported on piles, geotechnical engineers are required to formulate pile responses. Such a formulation involves the use of subgrade models that relate the interface forces to the displacement. The primary focus of this thesis is one such relatively new subgrade model, initially developed for shallow foundations, applied to laterally loaded piles. The model is a Kerr-equivalent two-parameter Pasternak-type continuum subgrade. Furthermore, as with most pile applications, the variable nature of the soil along the pile depth is also taken into consideration. The goal of this thesis is to investigate the applicability of the aforementioned model for predicting the static and dynamic inertial response of a single pile embedded in non-homogenous soils represented by a power function. To this end, the model in question is initially calibrated by setting equivalences between the responses predicted and results from finite element analysis. Expressions for a calibrating factor left open in the model are developed as functions of relevant parameters. The results from the calibrated model are compared with the results from the finite element method and found to be comparable. Additionally, it is demonstrated that the critical slenderness ratio and critical relative stiffness can be approximated by threshold values form expressions developed for the calibration factor. Using the calibrated subgrade model, the static response of the soil is also investigated. Expressions for the pile head flexibility influence factor and pile head stiffness terms are provided. The proposed expressions compare well with published results. In addition, utilizing the unique characteristic of the model being studied, in that the shear interaction is explicitly accounted for, its effects on static pile response are also studied. In general, neglecting the shear term results in overestimation of the pile head displacement. Similarly, the use of a calibrated lower order Winkler-type model that implicitly accounts for shear interaction is investigated which by in large provides higher displacement profiles. The calibrated model is also used in predicting the dynamic inertial response of a laterally loaded pile in non-homogeneous soil. An approximate energy method is used to arrive at the dynamic pile head stiffness and damping ratios. With the exception of fixed-head piles, it is observed that the dynamic pile head stiffness can reasonably be approximated by the static pile head stiffness for low ranges of excitation frequencies commonly encountered in seismic events. Curve fit expressions are also provided for the pile head damping ratio. The effect of shear interaction is also investigated for the dynamic inertial case. As the analysis is confined to long flexible piles, very little effect is observed with the exception of piles in rocking oscillation.Item Relationship between Water Content Ratio and Undrained Shear Strength of Fine Grained Soil(Addis Ababa University, 2023-07) Tigist Gemechu; Samuel Tadesse (PhD)Undrained shear strength of clay soil is a very important feature in geotechnical engineering. Obtaining undisturbed samples and testing them is a tough and time- consuming procedure; any experiment aimed at obtaining correlations between shear strength and consistency limits would be extremely beneficial. In this thesis, efforts have been made to obtain valid correlations between undrained shear strength and Water content ratio (WCR) for saturated soil samples and for unsaturated soil samples suction values were obtained from previous proposed mode of SWCC then suction value and undrained shear strength were correlate. For this purpose, Red clay soil samples collected from different sites in Addis Ababa city at the depth of 3m were used. In addition to collected soil samples secondary data were used. And for each samples Atterberg limits, Specific gravity, Sieve and hydrometer analysis, Compaction tests were conducted beside that by remolding these samples Unconfined Compressive Strength (UCS) tests were conducted. The best fit line, correlation, regression analysis, and comparison were performed using EXCEL. The findings are expected to have a wide range of applications in construction, making it easier for designers to produce a solid, cost-effective, and dependable design.Item Use of DCP and CBR Tests to Characterize Subgrade Shear Strength The Case of Volcanic Ash/Pyroclastic Deposit of Bulbula - Alage Section(Addis Ababa University, 2023-04) Yohannes Woldechirkos; Tensay Gebremedhin (PhD)The existing manuals adopted in Ethiopia for road construction and management purpose have made CBR and/or DCP tests mandatory in order to characterize strength of unbounded materials. Executing CBR and DCP tests is obligatory that, the data is available easily in every road stretch throughout the country. Contrary to this, the shear strength parameters used in slope stability analyses and bearing capacity computations are not available in sufficient number. For this reason, this research is initiated with the objective of obtaining values of shear strength parameters of pyroclastic/volcanic ash deposits using CBR and/or DCP test results on a pilot study area Bulbula – Alage road section. Different test results of Atterberg limit, sieve analysis, proctor, California bearing ratio, direct shear, dynamic cone penetration, field density, collapsibility and dispersity tests have been used. According to the test results, the plasticity of subgrade is low to none; the sand fraction is significant; the maximum dry density of the deposit is mainly below 1.5 g/cm3; the deposit has high CBR and low CBR swell values; DCP penetration rate decreases with depth in the majority of the stretch. The level of collapsibility potential is moderate with dispersity potential ranging from none to moderate. For this non-plastic to low plastic, low dry density, high CBR and moderate collapsible potential pyroclastic deposit a correlation is developed between CBR and/or DCP test results with that of angle of internal friction value obtained from direct shear test. The correlating equation has been developed using Excel and SPSS statistical analysis software.Item Reliability of Probabilistic Finite Element Method Over Deterministic and Traditional Probabilistic Method in Slope Stability Analysis(Addis Ababa University, 2022-04) Eleyas, Wolde; Tensay, Gebremedhin (PhD)Slope Stability is one of the crucial topics in geotechnical engineering to be investigated well because oftentimes slope exists naturally or formed artificially during construction of various civil engineering structures which needs to be at equilibrium. For that matter, there are various methods of analysis. For the last couple of decades, it is observed hard for Engineers to use Probabilistic Slope Stability Analysis due to many reasons. But these days, technological advancements which led to having more rigorous software packages made it be possible to use in the analysis and its merit. The aim of this thesis is to show the use of more reliable method of slope stability analysis for hypothetical back slopes in Addis Ababa where red clay soil is dominant and that is achieved by comparing methods based on a factor of safety, probability of failure, and reliability index. Limit Equilibrium Method (LEM) and Numerical Method are used for this purpose. Both deterministic and probabilistic analyses are carried on by modeling seven slope geometries with different input parameters from Addis Ababa ring road III project and hypothetical slopes using a two-dimensional Slope Stability analysis software called SlideV6.0. A Global Minimum type of analysis are carried on by using the Slide software. For finite element analysis and probabilistic finite element analysis, RS2 software from Rocscience is used. Uncertainty is accounted for in a better way in probabilistic analysis by defining parameters as a random variable in link with other features. It is shown by this study that, Probabilistic Finite Element Analysis (PFEA) seeks out the most critical slip surface than that of the finite element method. In addition, even if the factor of safety found from the deterministic analysis is greater than one still a probability of failure is observed. Moreover, it is attested that the factor of safety is not the only measure for slope stability, but other measures exist while using probabilistic analysis.Item 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-AdvisorThe 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%.Item Estimation of Soil Shear Strength Parameters from Index Properties Using ANN the Case of Addis Ababa(Addis Ababa University, 2022-05) Hanna, Yoseph; Tensay, Gebremedhin (PhD)Shear strength of a soil is perhaps the most important of its engineering properties, as stability analyses in the field of geotechnical engineering are dependent on it. This research work seeks to develop models for predicting the shear strength parameters (cohesion and angle of friction) of soils in Addis Ababa city using artificial neural network modeling technique; with a view to reducing time, effort and cost usually incurred in determining these shear strength parameters in the laboratory for future planning, design and construction projects in the study area. An attempt has been made to develop separate neural network models for c and ϕ from the index properties of soil consisting of Sand % (SP), Fines % (FP), Liquid limit (LL), Plasticity Index (PI), water content (ω), and Bulk density (BD) as input parameters. A multi-layer perceptron network with feed forward back propagation is used to model varying the number of hidden layers. For this purpose, 284 soil test result data was used. The geotechnical soil properties were determined in accordance with ASTM Standards. Direct shear box method was used to determine soil cohesion and soil internal friction angle. The developed models were found to be quite satisfactory in predicting shear strength parameters with correlation coefficients of about 0.98 and 0.92 for cohesion and angle of internal friction, respectively during the testing phase. The models are validated by primary soil test data and compared with some existing correlation methods. The result showed that the artificial neural network method gave better fit and accuracy than the selected empirical formulae in the prediction of shear strength parameters.