Geotechnical Engineering
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Browsing Geotechnical Engineering by Subject "Addis Ababa"
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Item Comparison of Retaining Structures Based on Their Performance (Case of Addis Ababa)(Addis Ababa University, 2018-05) Muhamed, Mula; Henok, Fikre (PhD)Deep basement constructions are always anticipated in densely populated and urban areas with limited construction spaces like Addis Ababa. The design of basement retaining walls and their supporting system involves careful analysis, design and monitoring due to the sensitivity of ground movements that can cause damage to the adjacent buildings, roads and other utilities. Therefore, analyses and parametric study are important to better understand the response of the soil to excavation and to predict the magnitude and pattern of ground movement. In Addis Ababa the most common type of retaining wall for deep excavation is contiguous bored pile wall. This retaining method may not be relatively effective in terms of various parameters like soil type of the area, embedment depth, size of the wall, and construction cost. Thus other alternative retaining systems should be considered and analyzed to select a best option. There are papers written to analyze the performance of different types of retaining structures. The results presented in those papers are for a specific type of retaining structure and lack cost estimation. These two factors limit the flexibility to compare results in an organized manner and have reasonable up-to-date information about the construction cost. Therefore, it is necessary to compare soil retaining structures used for deep excavations by including additional comparison factor, which is cost of construction. The objective of this thesis is to identify the effect and performance of diaphragm, contiguous and tangent bored pile retaining walls for basement work in terms of bending moment, shear force, lateral wall deflections and ground movements by varying wall types, varying size of the wall and varying wall embedment length during stages excavation using the software package PLAXIS 2D version 8.2 for the chosen case study. Besides that, to determine the appropriate wall type for basement based on economical aspect. Results of these analyses were recorded in terms horizontal displacement of the wall, ground settlement behind the wall, shear force and bending moments induced in the wall due to an adjacent deep excavation. And those Results from software analysis will be compared with each other to select the best option which is worth to consider based on their performance. And also they will be compared based on the cost which the walls worth’s.Item A Study of Dynamic Properties of Soils Found in Yeka subcity Area of Addis Ababa(Addis Ababa University, 2020-01) Natnael, Bekele; Alemayehu, Teferra (PhD)Yeka sub-city is located in the North East part of Addis Ababa. The geographical location of Yeka subcity is 9 0 ’ 12 0 latitude N and 38 50’ E longitude. The subcity is characterized by variable topographic features. Addis Ababa is located in seismic zone 3 according to ES EN 2015. The city has moderate seismicity. However, if damage occurs due to moderated seismic activity, its effect might be significant compared to an earthquake occurring on remote areas. Yeka subcity is one of the highly populated areas of Addis Ababa. To reduce future seismic damages, it’s necessary to determine the response of soil deposits in the subcity .Hence the objective of this research is to investigate the dynamic properties of soils found in Yeka subcity. The index properties investigated in this study include; particle size analysis, atterberg limits, free swell and specific gravity. The result of the study showed that, liquid limit ranges from 53 to 85 %, plasticity index ranges between 23 to 45 %, specific gravity values are between 2.61 to 2.71 and free swell ranges 59 to 128 %. . According to Unified Soil Classification System, common soils found in Yeka subcity are classified as elastic silt and plastic clay. In this paper, the shear modulus and damping ratio values of soils commonly found in Yeka subcity was determined using cyclic simple shear test machine on undisturbed samples. The tests were conducted as a function of strain amplitude of 0.01 %, 0.1 %, 1 %, 2.5 % and 5 % under axial stress of 100 kPa, 200 kPa, and 400 kPa. The normalized shear modulus values were determined and the results were compared with curves developed by (Seed and Idriss 1970; Vucetic and Dobry 1991; Dimer 2013; Gemechu 2011; Mengistu 2014).The results reveal that the normalized shear modulus values at lower strains (< 0.01 %) are lower than published literature data. This reduction in values could be due to sample preparation and testing condition. However for higher strains, the computed shear modulus values are within the limits indicated in published literature data.Comparisons were also made with local soils. The shear moduli of the studied soils are fitted well with curves developed for clay soils of Arbaminch and very close to silty soils of Adama. However, the values show slight scatter with silty soils of Ziway. The determined damping ratio values for confining stress of 100 and 200 kPa are within the curve provided by Seed and Idriss (1970) for saturated clays. However, for confining stress of 400 kPa the values are outside the limits.Item Unsaturated Shear Strength Characteristics and Stress Strain Behavior of Expansive Soils of Addis Ababa(Addis Ababa University, 2010-11) Habtom, Gebre; Hadush, Seged (PhD)Considerable research work has been done on the shear strength properties of most soils. However, very little information is available on the shear strength characteristics of expansive clays. This work studies the shear strength characteristics of an expansive unsaturated soil found in Addis Ababa. Matric suction is one of the stress state variables that control the shear strength of unsaturated soils. Previous studies on the expansive soils are done using the conventional triaxial machine, which is unable to measure matric suction of the soil. The main aim of this study is to determine the unsaturated shear strength properties and the stress strain behavior of expansive soil found in two locations (Bole and CMC) in Addis Ababa. The shear strength behaviour of unsaturated soil is studied in this work using the consolidated undrained modified triaxial compression equipment with measurements of matric suction during the shearing stage. In this work, modified consolidated undrained tests were conducted on 12 undisturbed potentialy expansive soil samples collected from Bole and CMC area at 2.5m depth. Six of the tests were on completely saturated samples and the other six on unsaturated samples. Range of values of shear strength parameters (c, ∅’, and ∅b) were obtained from the consolidated undrained test depending on the applied matric suction. According to the outcome of the research, the deviator stress of soils from Bole area ranges from 90.65 kpa to 130.08 kpa for effective consolidation of 250 kpa for matric suction range of 0 Kpa to 75 Kpa. Similarly the soils from CMC area ranges from 54.03 to 93.41 kpa in deviator stress for effective consolidation of 150 kpa and for matric suction range of 0Kpa to 75 Kpa. The result clearly shows that the shear strength of expansive soils tested for unsaturated case is higher than that of saturated soil and the shear strength increases when matric suction increases.