Geotechnical Engineering

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Browsing Geotechnical Engineering by Author "Abebe, Tadesse"

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    Investigation into Some of the Engineering Properties of Soil in Woldiya Town
    (Addis Ababa University, 2014) Abebe, Tadesse; Tadesse, Samuel (PhD)
    Woldiya is a hillside market town, capital of the Semien Wollo Zone, and Woreda in Northern Ethiopia. Located North of Dessie and Southeast of Lalibela in the Amhara Region. This town has a latitude and longitude of 11°50′N, 39°36′E and an average elevation of 2112 meters above sea level. A lot of civil engineering structures are under construction; however, nothing has been done on the investigation of soil with respect to the intended urban development plan. Therefore, the objective of the research is to investigate some of the engineering properties of soils found in Woldiya town. The engineering behavior of soils formed under temperate or tropical conditions is determined by certain physical characteristics designated as engineering properties. In practice the determination of all the engineering properties of soils is expensive and time consuming. Whereas, Index properties are simpler and cheaper engineering characteristics which are indicative of some engineering properties and essential parameters for soil classification. To achieve the aim of the thesis disturbed and undisturbed samples from different parts of the town were collected and laboratory tests were done. The index property investigation in this study includes; natural moisture content, specific gravity, particle size distribution, Atterberg limits and free swell tests. Furthermore, the consolidation and shear strength characteristics of soil in the town were studied. The grain size analysis test result showed that the dominant proportion of soil particle in the research area is fine-grained soils, which have clay content ranging from 6-50%, silt faction 40-63% sand fraction 2- 20% . The result of Atterberg Limit test on the soil in the research area showed a liquid limit ranging from 34- 97%, plastic limit ranging from 28-35% and plastic index from 5-63%.The specific gravity ranges from 2.65-3.0. Free swell test conducted on the samples collected shows range from 39-130%. The shear strength of a soil mass is the internal resistance per unit area that the soil mass can offer to resist failure and sliding along any plane inside it. Shear strength is the principal engineering property which controls the stability of a soil mass under loads. It governs the bearing capacity of soils, the stability of slopes in soils , the earth pressure against retaining structure and many other problem. Disturbed and undisturbed samples were collected during the driest season. The soil was very stiff, when try to do unconfined compression test it shows crumble before the run of the test. Because of this reason it is impossible to do unconfined compression test in this thesis. Even though, unconfined compression test is not done, direct shear test was done to show the shear strength of soil in the town. The cohesion and IX internal friction of the representative samples of test pit four and five are (64.83kPa,17.850) and (91.56kPa,19.650) respectively. According to the Unified Soil Classification System, the soil is categorized mainly as clay soils and partially silts soils. The AASHTO Classification System shows that the usual types of significant constituent materials of the Woldiya soil are clayey soil. Finally one-dimensional consolidation tests were done and have compression index ranging from 0.28-0.4, recompression index ranging from 0.05-0.07, coefficient of consolidation ranges from 0.031-0.039cm2/sec.