DSpace Collection: Thesis - Geotechniques
http://etd.aau.edu.et:80/dspace/handle/123456789/496
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CORRELATION OF CBR VALUE WITH SOIL INDEX PROPERTIES FOR ADDIS ABABA SUBGRADE SOILS
http://etd.aau.edu.et:80/dspace/handle/123456789/4933
Title: CORRELATION OF CBR VALUE WITH SOIL INDEX PROPERTIES FOR ADDIS ABABA SUBGRADE SOILS
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<br/>Authors: Yared, Leliso
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<br/>Abstract: The unique nature of soil properties as it appears naturally is that being divergent spatially and seasonally beyond the designerâ€™s control. Geotechnical engineers usually attempts to develop empirical equations specific to a certain region and soil type. However, these empirical equations are more reliable for the type of soil where the correlation is origin. Hence, it is important to develop empirical equations that best fit for the local area that we can access.
As a result, this study evolved to find the correlation between CBR values with soil index properties specific to Addis Ababa subgrade soils. The study has examined the feasibility of single linear regression analysis and multiple linear regression analysis in correlating CBR value with soil index properties. Accordingly, forty two disturbed samples collected from different parts of Addis Ababa and the required laboratory tests have been conducted in order to achieve the intended correlations.
Specific to this research, statistical software (SPSS) is employed to investigate the significance of individual independent variables. The correlation is established in the form of an equation of CBR as a function of grain size parameter, Atterberg limits and compaction parameters by considering the effect of an individual soil properties and effect of a combination of soil properties on the CBR value. The developed correlation entailed a moderate determination coefficient of R2 = 0.458 using single regression analysis, while multiple regression analysis generated relatively an improved correlation of R2 = 0.629, for a sample size of forty two. After validating the developed correlation with control test results, it was noted that the correlation of CBR value with soil index properties is more applicable for preliminary characterizing the strength of subgrade soils.UNSATURATED SHEAR STRENGTH CHARACTERSTICS AND STRESS - STRAIN BEHAVIOUR OF SILT SOILS OF HAWASSA
http://etd.aau.edu.et:80/dspace/handle/123456789/4860
Title: UNSATURATED SHEAR STRENGTH CHARACTERSTICS AND STRESS - STRAIN BEHAVIOUR OF SILT SOILS OF HAWASSA
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<br/>Authors: EYOB, TEFERI
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<br/>Abstract: Most of the shear strength tests and studies done in this country particularly in Addis Ababa are using the conventional triaxial machine, which is unable to measure the matric suction of the soil. However, a few research works have recently been done on the shear strength characteristics for unsaturated soils in Addis Ababa. These previous studies on the unsaturated soil are only on red clay and expansive soils of certain areas of Addis Ababa and a single study on Arbaminch expansive soils. This thesis provides the results of triaxial tests which were carried out to study the unsaturated shear strength characteristics of Hawassa silt soil with suction measurement. The soil tested was reconstituted using dynamic compaction. Consolidated undrained (CU) triaxial tests were performed on both saturated and unsaturated samples.
In this work, disturbed silt soil samples were collected from test pits dug to a depth of 2.5m and the shear strength tests were conducted on compacted samples. The saturated shear tests were carried out for consolidation pressures of 100 kPa,200 kPa and 300 kPa.The unsaturated shear tests were carried out for same net confining pressure of 200 kPa but with varying matric suctions of 30 kPa,60 kPa,100 kPa,120 kPa and 150 kPa. All the specimens tested were compacted at the same initial moisture content and dry density corresponding to field conditions.
The results from the consolidated undrained triaxial tests disclosed that as the matric suction increases from 0 to 150 kPa, the maximum deviator stress increases from 202.48 kPa to more than double of 443.14 kPa under the net confining pressure of 200 kPa. This signifies that shear strength of the silt soil sample considerably increases due to matric suction and the rate of increase has been found to be significantly higher compared to what was observed in clays under unsaturated condition. Moreover, the shape of the stress-strain curve of the unsaturated cases resemble that of the saturated samples and for almost the whole range of the applied matric suction, the increase in matric suction did not affect the shape of the stressâ€“strain curve.A STUDY ON THE DESIGN AND ADVANTAGE OF CONICAL TYPE SHELL FOUNDATION USING ANALYTICAL AND FEM
http://etd.aau.edu.et:80/dspace/handle/123456789/4859
Title: A STUDY ON THE DESIGN AND ADVANTAGE OF CONICAL TYPE SHELL FOUNDATION USING ANALYTICAL AND FEM
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<br/>Authors: Endalkachew, Taye
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<br/>Abstract: This thesis introduces shell foundations in general and conical type shell foundation in
particular as an alternative to the conventional plain foundation. The different types of
shells that may be employed in foundations are introduced with their geometry and
applications under different situations. Shell foundations can be used as combined or
isolated footing. The simplest form of shell appropriate for isolated footing is conical
shells. Conical shells are employed as an alternative to plain circular footings.
The design of conical shell foundation is based on membrane theory in order to
determine membrane stresses, and ultimate strength theory to obtain the ultimate load
which enables to compute the load factors involved in the design. A design example is
provided and comparison is made with plain circular footing. The result clearly indicates
that conical shells save more material than do so plain circular footings.
A finite element analysis is carried out using the finite element software PLAXIS for
different soil properties and footing size. The analysis was performed for conical shells
and plain circular footing in order to compare the results. The finite element analysis
results prove that conical shells have high load carrying capacity than circular footing
under same soil properties.
Shell foundations need smaller quantities of material than the conventional plain
foundations. In a country like Ethiopia where material to labor cost ratio is high, shell
foundations may be used as an economic alternative.Prediction of swelling behavior of Addis Ababa expansive soil using simple mathematical model
http://etd.aau.edu.et:80/dspace/handle/123456789/4858
Title: Prediction of swelling behavior of Addis Ababa expansive soil using simple mathematical model
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<br/>Authors: ELEYAS, ASSEFA
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<br/>Abstract: Damage due to soil swelling is very noticeable in wide spectrum of structures such as
roads, buildings, canal linings, landfill liners, etc. To evaluate severity of swelling and to
design for the best and most economical stabilization strategy, an accurate assessment of
the swell potential is required.
The main reason of swelling behavior is water absorption of soil mass in time. And the
time required for completion of swelling is relatively long. In view of that several
attempts have been made by researchers to obtain time-swell relationships for expansive
soils. Some progress has been made toward characterizing swelling characteristics,
despite the complexity of the behavior.
In this study a simple hyperbolic mathematical model is used to predict the swelling
behavior of an expansive soil from Addis Ababa. The formula was first proposed by
Richard and Abbot, 1975.
The model was formed in one equation with many parameters. The main advantage of
this model is that only one parameter is needed to run the model. The main parameters
that are needed to run the model are the applied pressure and initial dry density. The other
parameters of the model including the initial slope of the swell-time curve, the final
slope, the reference swell, and the peak swell were investigated experimentally.
Based on the experimental results, empirical relationships were developed for
determination of these parameters as functions of the applied pressure and initial dry
density. The model prediction were compared with the experimental results and showed
good agreements for all levels of applied pressure and initial dry density of the tested soil.