Browsing by Author "Haile, Mesele (PhD)"

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    Compaction properties of lateritic soils (The Case of Assossa)
    (Addis Ababa University, 2008-04) G/medhin, Amare; Haile, Mesele (PhD)
    High temperature and moisture fluctuating in tropical areas, enhancing chemical weathering leads to the formation of lateritic soils when the soil is well-drained. These highly weathered tropical materials may irreversibly change properties when dried, and even simply remoulding the material may cause significant change in properties. Embankment construction is one of the major activities in Civil Engineering works, which enhance development. Hence, great attention has to be given during construction of such infrastructures when using the tropical soils as construction materials. Embankments which are constructed using lateritic soils have a great advantage in that they are constructed from locally available materials within sound technical and affordable financial capacity. To use lateritic soils safely and economically, appropriate methods of determining the geotechnical properties, compaction properties, shear strength parameters, unconfined compression strength (UCS) have to be investigated and developed. Accordingly, in this paper the compaction properties of lateritic soils which are taken from Assossa have been investigated. In addition to this, some peculiar geotechnical and geochemical characteristics of these soils have been studied. Accordingly, the soils from Assossa have been obtained to be true lateritic as the geo-chemical test and tests from laboratory indicated. The soil samples were compacted at optimum moisture content, at drier side of the optimum moisture content and at wetter side of the optimum moisture contents. Then, the UCS tests were done on the soil samples to investigate the variation in strength properties as a function VIII of time after compaction of these soils. Keeping the compacted lateritic soil samples for a longer period shows an increase in the UCS values and samples compacted at optimum moisture content have higher values of UCS as compared to the once on the drier and wetter sides. Compaction of these soils has been influenced by depth, drying, mineralogical composition and compaction energy as illustrated in this thesis. Moreover, the effect is higher as the degree of laterization increases. The effect of permeability of compacted lateritic soils in relation to change in compaction moisture content and time effect after compaction were investigated.Acordingly, the effect of compaction moisture shows that permeability decreases towards the optimum moisture content. In addition to this, the time effect after compaction has been investigated and the test showed that permeability decreases as time after compaction increases. The soils are less sensitive to expansion when there is fluctuation of water. Further, the soil is highly sensitive to remoulding of samples as the compaction curves and the degree of sensitivity showed.
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    Developing Supporting Software for Analysis. Design and Cost Estimation of Commonly Used Reinforced Condrete Foundations
    (Addis Ababa University, 2003-07) Shibru, Mekonnen; Haile, Mesele (PhD)
    Key words: Supporting Analysis And Design Software;Supporting Cost Estimation Software; Foundation Selection. The choice of the most appropriate type of foundation for structures is one of the challenges a civil design engineer faces. Different structural systems and loads from the super structure, hetrogenous soil conditions and variations of soil strength parameters with change in soil moisture makes determining the most appropriate foundation type a tedious process. Besides engineering consideration ,the variation in cost of construction materials and labour for the different foundation types and for different locations of projects makes the choice of the most appropriate foundation (function and cost) an extremely time consuming process. This practical difficulty has led most design engineers to opt for one type of foundation based on engineering judgment and experience. This not so rational process is not expected to lead to optimal design , it may even end up with erroneous design. In this thesis an attempt is made to develop a computer program that requires super structural input as foundation reaction and soil data and does analysis. Once design is completed the quantity of material and labour is calculated and cost comparison is made. Ultimately the functional best and economical foundation type is chosen in a matter of minutes. This enables design engineers to get an optimal solution in the foundation system at the same time saving design time.
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    Investigating the Index Properties of Residual Tropical Soils of Western Ethiopia (The Case of Asossa) BY Fekede Wakuma January
    (Addis Ababa University, 2007-01) Wakuma, Fekede; Haile, Mesele (PhD)
    The engineering behavior of soils, wheather formed under temperate or tropical conditions, is determined by certain physical characteristics designated as engineering properties. In practice, since the determination of all the engineering properties of soils is expensive, often index properties, simpler and cheaper engineering characteristics which are indicative are investigated. Residual soil is a soil material derived from the in-situ weathering and decomposition of rock, which has not been transported from its original position. Residual tropical soils can have characteristics that are quit distinctively different from those of transported soils, That is: the conventional concept of soil mechanics is not applicable to many residual soils as it consists of aggregates or crystals of weathered mineral matter that break down and become progressively finer under continuous manipulation. Western part of Ethiopia is characterized by such soils. As mentioned in ERA (Ethiopian Roads Authority) design manual (ERA, 2001) Residual laterites are widely available soil material in these areas. The index properties of such soils have not been studied in detail as per the test recommendations for residual tropical soils. This Thesis is conducted to indicate the index properties of soils of Asossa Town (Capital of Beneshangul Gumuze), which is located in western Ethiopia and covered by residual soils. In this thesis work, the index properties of residual tropical soil have been investigated on the soil specimens taken from Asossa Town by following the test procedures recommended for residual soils. The specimens were tested at different sample preparation conditions prior to conducting the laboratory test and resulted in different end values. The index property investigation in this research includes; Specific Gravity Test, Particle Size Distribution, Atterberg xiii Limit Tests and Free Swell Tests, all tests were conducted at three different test temperatures (at received moisture, air-dried and oven dried at a temperature of 105o c ). Generally it was found that, sample pre-treatment and commonly used soil test procedures for temperate soils when applied to Asossa soils resulted in completely altered test result as compared to the actual test result values obtained by following testing procedures recommended for tropical soils. It was found that there is considerable structural water that could be destroyed by oven drying at a temperature of 105 degrees and must be deducted from every moisture content determinations in Atterberg Limit tests. Sample manipulation is also found to alter the results of the Atterberg Limit values by affecting the bond between soil structures. Therefore, the appropriate test procedures for tropical soils are strongly recommended for research and practical engineering application where such soils are likely to exist.
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    Investigation into the appropriate laboratory testing procedures for the determination of the index properties of the Lateritic Soils of Western Ethiopia (Nedjo-Jarso-Begi Road area)
    (Addis Ababa University, 2009-11) Million, Wossen; Haile, Mesele (PhD)
    The appropriate laboratory testing procedures while carrying out index property tests of lateritic soils found in western Ethiopia (Nedjo, Jarso and Begi areas) have been investigated. Classification and composition of these soils have also been studied. The X-Ray Diffraction (XRD) analyses revealed that the soils in these areas are composed of minerals of Kaolinite and Smectite groups; such as Kaolinite, Quartz, Hematite, Vermiculite, Dickite, Borax, Illite, Nacrite. The X-Ray Fluorescent (XRF) analysis showed that there is a high concentration of sesquioxide minerals and there is no amorphous material present in the soils. Comparison between the moisture contents determined using air drying (or alternatively 50oC oven drying temperature) and that of 105oC oven drying temperatures indicates that there is no significant amount of structural water; however, comparing to the non-lateritic soils from Addis Ababa, the western Ethiopia lateritic soils have some amount of structural water or water of hydration. In the analysis of Atterberg Limits, in majority of the soils difference was observed between the Atterberg Limits obtained from test on a specimen mixed for 5min and that of 30min, this indicates that the cementation of the clay particles is to be disaggregated with higher mixing time. Analysis of specific gravities of the soils using various pretreatment and testing procedures showed that, increase in drying temperature from its in situ condition to an air-dried or equivalent of 50oC oven drying temperature and further to 105oC oven drying temperature reduces specific gravity of the soils. Analyses of the grain-size distributions (grading curves) with respect to the effects of different testing procedures (pre-test treatment methods), the effects of specific gravity variation within a sample, and the variation of sample location /depth/ and other physical properties indicated that the soils were not homogeneous within the laterite zone. The dry sample preparation and testing procedures tends to decrease the percentage of coarser particles as the coarser particles became highly fractured during the pulverization process. As a result these dry sieving techniques were found to be inappropriate. The analyses of the grading curves using mass proportion and the modified grading curve using volume proportion, which uses separate specific gravity, showed that the two grading curves are nearly the same; hence, the need of modifying the grading curves by volume proportion is not as such important especially when wet sieving method is used. Moreover, the analysis of grading curves with respect to sampling depth showed that, generally, the soils become coarser as the sampling depth increases. This confirms that the degree of weathering decreases with depth. Soil classification using Unified Soil Classification System (USCS), AASHTO Classification System, Wesley’s Classification Method (classification using mineralogical composition) and soil grouping using genetic basis and soil forming factors were analyzed. According to the USCS chart the soils under investigation falls in the MH zone, which means that the soils have ‘poor’ engineering properties that are considered unsuitable for various engineering purposes. However, in practice, such soils frequently have good engineering properties especially for construction of sub grades and embankments. Contrary to the USCS, the AASHTO Classification System classify majority of the soils under sub group A-2-7 with a group index less than 4, which mean the soils are good sub grades and embankments construction materials. Using the Wesley’s Classification Method the soils fall under Group C, sub-group (c). Soils under this group have good engineering properties. The soils under investigation have fallen under ferrisols group where erosion has kept pace with profile development. The analysis of the test results obtained from different laboratory testing procedures used for moisture content, plasticity tests, grain-size analysis and specific gravity tests for the lateritic soils found in Western Ethiopia has shown that the soils are sensitive to the type of testing procedures as a result an appropriate laboratory testing procedures attached in Appendix-A are proposed.
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    Performance of Unconventional Soil Stabilizers in Stabilization of Substandard Materials for Road Subgrade & Subbase
    (Addis Ababa University, 2010-06) Ashuro, Tesfahun; Haile, Mesele (PhD)
    Road connectivity is one of the key components for development, as it promotes access to economic and social services, generating increased income and employment. However, the construction of such economically vital sector is the most expensive of public works project undertaken by the society. Traditional pavement design and construction practices require high quality materials to fulfil minimum construction standards. In many of road projects it is very difficult to get standard materials with in economical haul distances. There is an increasing effort around the world towards introducing innovative and unconventional road construction approaches that aim at reducing costs of construction by enabling use of marginal materials found with in the road route. One of proven technologies in connection to this effort is stabilization of soil. Stabilization can be derived from thermal, electrical, mechanical or chemical means. Chemical stabilizers can generally be categorized in to two broad categories: conventional and unconventional stabilizers. Traditional stabilizers such as cement lime, fly ash, and bituminous products have been intensely researched, and their fundamental stabilization mechanisms have been identified. Unconventional soil stabilization additives consist of a variety of chemical agents that are diverse in their composition and in the way they interact with the soil. Unfortunately, relatively little is known about their interaction with geotechnical materials or their fundamental stabilization mechanisms due to proprietary nature of commercial stabilization additives, their exact chemical compositions are not disclosed. In this research two unconventional stabilizers were used for investigation of their effect on the engineering properties of soils that are deemed to be marginal for road subbase and subgrade. The two stabilizers used were: PURE CRETE and Anyway Natural Soil Stabilizer (ANSS). ANSS Natural Soil Stabilizer is claimed to be inorganic, hydration activated powderbased stabilizer that reacts with the soil particles to create layers that are interconnected through a complex inter-particle framework. The manufacturer claims PURE CRETE to be a complex non-bacterial concentrated multi-enzymatic formulation that alters the properties of earth materials, providing one of the most cost effective methods to stabilize roads and seal ponds and landfills. The stabilizers were combined with a total of five different soils with classifications according to AASHTO as A-7-5, A-7-6, A-2-7, A-2-4, and A-2-6. ANSS stabilization induced the most improvement on engineering properties of all soils tested at manufacturer recommended dosages and PURE CRETE failed to show any improvement at manufacturer recommended application rate. However, at very high application rates modest effects were noticed. It is recommended based on the results of this research that ANSS can be considered as a viable option for stabilization of subgrade soils after conducting durability tests. It will particularly help use of marginal materials where materials that met standard specifications are far away.
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    Strain-Rate Influence on Shear Strength Characteristics of Compacted Asela Clay
    (Addis Ababa University, 2016-10) Tafa, Gezahegn; Haile, Mesele (PhD)
    This research work tries to examine the effect of strain rate on shear strength of red clay soil of Asela. It is attempted to identify the effect of strain rate by conducting a series of triaxial compression test and unconfined compression test on remolded soil samples. All the specimens were compacted at optimum moisture content (OMC) with the standard compaction apparatus. Besides basic tests have been done to identify the soil type. Both unconfined compression tests and triaxial tests were done on samples of 38mm in diameter and height twice the diameter. The type of triaxial test employed was consolidated undrained (CU) with pore pressure measurement and with effective consolidation pressure of 200kPa, 300kPa and 400kPa. After saturation and consolidation stage, the specimen were axially loaded at rate of strain varying from 0.001mm/min to 1mm/min. A total of twelve triaxial consolidated undrained tests and sixty unconfined compression test were run. Data presented includes consolidation data, pore pressure observation, stress-strain relationship and modified Mohr failure envelop diagram. The results of triaxial tests were used to examine the stress strain relationship and shear strength parameters. The results showed that strain rate affect both stress-strain relationship and strength of soil. As the strain rate increases the strength of the soil also increase but the strain rate has more pronounced effect on cohesion and little effect on angle of internal friction of the soil. The values of cohesion obtained from modified failure envelop for strain rate 0.001mm/min,0.01mm/min,0.1mm/min and 1mm/min were 40.67kPa, 44.38kPa, 64.6kPa and 93.15kPa for total stress and 39.97kPa, 42.85kPa, 51.92kPa and 79.52kPa for effective stress. The value of angle of internal friction obtained from modified failure envelop for strain rate of 0.001mm/min,0.01mm/min,0.1mm/min and 1mm/min are 14.460,14.530, 14.120 and 14.730 for total stress and 21.870,22.130,21.530 and 21.020 for effective stress. The unconfined compression test were done on the samples of 38mm in diameter and a height of twice the diameter with seven(7) different strain rates(i.e.0.08,0.4,1,1.52,2,5 and 10mm/min) for remolded clay soils. From the test result undrained shear strength in unconfined compression test is directly related to strain rate effects. A higher strain rate results in higher undrained shear strength for Asela red clay soil. The values of undrained shear strength obtained from unconfined compression test for strain rate of 0.08mm/min, 0.4mm/min, 1mm/min,1.52mm/min, 2mm/min, 5mm/min and 10mm/min are 34.02kPa, 36.95kPa, 37.23kPa, 41.77kPa, 42.70kPa, 47.77kPa and 48.46kPa
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    Study of Index Properties and Shear Strength Parameters of Laterite Soils in Southern Part of Ethiopia the Case of Wolayita - Sodo
    (Addis Ababa University, 2008-05) Tibebu, Hanna; Haile, Mesele (PhD)
    Most geotechnical problems such as bearing capacity, lateral earth pressure and slope stability are related to the shear strength of a soil. The shear strength of a soil can be related to the stress state of the soil. The stress state variables generally used for an unsaturated soil are the net normal stress (_ –ua) and the matric suction. (Ua- Uw).The index properties of soils are also essential parameters for soil classification as well as for indirect estimation of its potential strength. Because of climatic conditions, ground water tables in tropical and subtropical regions are often depressed. Evapotranspiration often exceeds infiltration. This leads to deep desiccation of the soil profile. Therefore, residual soils frequently exist in an unsaturated state with continuous air in their voids. The pore air pressure will usually equivalent to atmospheric pressure, but the pore water pressure will be sub – atmospheric, i.e. negative due to capillary effects in the small pores of soils. This negative pore water pressure or suction produces an additional component of effective stress, or in other words: the effective stress becomes greater than the total stress. The extended Mohr Circle failure envelope defines the shear strength of unsaturated soil. Identifying the soil characteristic is essential to determine the type of test and test procedure that is applied during sampling, sample preparation and testing. In this thesis, several tests have been conducted to understand the effect of unsaturated soil mechanics on the determination of shear strength parameters and comparison of the result with tests on saturated samples. To this effect the geotechnical and geo-chemical characteristics of soils sampled from Wolayita – Sodo have been investigated. For shear strength parameters determination, undisturbed soil samples were collected and unconsolidated undrained tests and unconfined compression tests were carried out because of the triaxial machine’s limitation to suction measurements. Both saturated and unsaturated tests were conducted to make systematic comparison of the test results. xi Moisture content determination, using oven temperatures of l05°C, 50°C and 35°C were carried out on the soil samples to investigate the variation of structural water. Atterberg Limits were investigated for different testing procedures on the soil samples to evaluate the effect of test manipulation on cement bonds between clay clusters. The liquid limit tests were carried out on soil specimens mixed for 5 minutes and 30 minutes durations. From the test results, the soil under investigation has been affected by manipulation. Specific Gravity Test, Particle Size Distribution, Atterberg Limit Tests and Free Swell Tests were conducted at three different test temperatures (as received moisture, air-dried and oven dried at a temperature of 105°c). These tests were conducted in order to understand the behavior of the soil in the area and classification. According to the result of this research, Moisture content ranges between 26 - 41%, Plasticity Index ranges between 19 – 30%, Clay fraction ranges between 48 - 70, Shrinkage limit ranges11-22, Free swell ranges between 28-38% and Specific Gravity ranges between 2.61- 2.97. The shear strength parameters(C - _ value) as determined from UU Test ranges between 150-173 Kpa and 12 º -20 º for unsaturated sample respectively. For saturated soil sample, the C- value obtained is 118Kpa and unconfined compression strength (qu) ranges from 215- 385 Kpa. Laterite soils are characterized by high concentration of Iron Oxide, Aluminium Oxide (Sesqueoxide) and Kaolinite minerals. The soils samples subjected to tests fall below A-line under MH (inorganic clay with medium strength) and contain Kaolinite mineral. The activity number which is the ratio of plasticity index to the percent of clay –size friction by weight, is below 0.75, confirming that the soil is inactive.