Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Access Right: Open AccessAuthor: search.filters.author.Ecemiş, Nurhan

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  • Master Thesis
    Discrete Element Modelling of Cpt Using Shaking Table Tests in Sands
    (Izmir Institute of Technology, 2014) Bakunowicz, Paulina; Ecemiş, Nurhan
    This thesis contains an overview of the results obtained from detailed study exploring the ability of two-dimensional discrete element method (2D DEM) models to reproduce cone penetration tests in saturated sand deposits. The simulations of the cone penetration and triaxial tests are carried out under application of the commercially available numerical analysis software PFC2D (Itasca, 2008). This software is based on DEM with additional basic fluid analysis option. The soil sample used in the laboratory experiments was uniform, river clean quartz sand, which was similar to Ottawa sand. The material properties that required calibration were normal stiffness, tangential stiffness and interparticle friction. These parameters were determined by trial and error from 2D DEM biaxial test simulations. Data from five laminar box shaking table tests of saturated sand was analysed with particular attention to the measured cone penetration resistance in assemblages deposited at various relative densities. Each shake table test was subjected to three series of shaking tests (at the same intensities) by using one-degree of freedom shaking table system, which allowed obtaining wide scope of different porosities. A new scaling factor was implemented in order to compare the data obtained from tests on real soil (3D) with numerical simulations by DEM (2D). Observations of the behaviour of discrete material at laminar box enabled us to make a correlation between porosity from large scale experiment and PFC2D model. To examine the effects of boundary conditions, porosity, particle diameter size, fluid grid dimensions, contacts, coordination number and others on the tip resistance value, multiple simulation tests were performed. From the results presented we can deduce that 2D DEM CPT model can be powerful tool to enrich the conventional physical calibration tests. In this thesis it is also proven that CPT laminar box based correlations facilitate to overcome limitations of 2D simulation and can be widely and successfully applied for both scientific research and engineering practice purposes.
  • Master Thesis
    Effects of Consolidation Characteristics on Cpt Cone Resistance and Liquefaction Resistance in Silty Soils
    (Izmir Institute of Technology, 2013) Karaman, Mustafa; Ecemiş, Nurhan
    One of the most important reasons of the life and property losses caused by earthquakes is liquefaction during or after the earthquakes. Many researches focused on liquefaction after the earthquakes have revealed that liquefaction occurs mostly in silty soils. Empirical relationships between normalized cone penetration resistance (qc1N), cyclic resistance ratio (CRR), magnitude of earthquake (Mw), and silt content (FC), derived from field observations, are currently used for liquefaction potential assessment of loose saturated sands and silty sands. However, the effects of fine content on liquefaction resistance and penetration resistance are not defined clearly in these researches. For this reason, it is aimed to investigate the effects of fine content on consolidation characteristics and the effects of coefficient of consolidation on liquefaction resistance and cone penetration resistance. In this study, a number of field and laboratory studies were carried out to investigate the existing relationships. According to the results of experimental studies, first, the effects of the fines content on coefficient of consolidation and drainage characteristics of soils for different soil density ranges are examined and it is established that, both the fines content and the relative density effect the coefficient of consolidation of the sands and silty sands. Second, the changes in cone penetration resistance are investigated for different range of fines content and the relative density which have significant influence on coefficient of consolidation. It has been realized that the coefficient of consolidation indicates a significant influence on the measured penetration resistance during penetration of the CPT cone to the soil having different relative density, and it is figured out that for stiff-dense to medium dense soil, the decrease of normalized cone resistance is observed due to the change in drainage characteristics of fines or coefficient of consolidation. On the other hand, for loose soils only the relative density indicates a significant influence on the measured CPT penetration resistance around the probe. Finally, the contribution of the relative density on the liquefaction resistance of soils is observed at different fines content and compared with the available method in the literature.
  • Master Thesis
    Seismic Liquefaction: 1-G Model Testing System and Shake Table Tests
    (Izmir Institute of Technology, 2013) Kahraman, İrem; Ecemiş, Nurhan
    Soil liquefaction is a crucial, interesting and complex seismic problem. Previous earthquake records and computational modelings have given general information about liquefaction, but many questions, such as; effects of silt content on liquefaction phenomena have not been clearly answered yet. In this study, liquefaction phenomena in sands and silty sands were simulated by a large scale 1-g laminar box system. Three shake table tests were performed, where each test consisted of four shakes to analyze the initial-liquefaction and re-liquefaction phenomena. Instrumentations were used during shake table tests to measure laminate, soil response and settlement of ground. The soil deposit was prepared with different fines content using hydraulic filling method. Piezocone penetration tests (CPTu) were conducted, before and after each shake to determine the relative density of the soil model. Following results were found; Silty sands were found to possess more liquefaction resistance than uniform fine sands. Soils with rounded shapes were more susceptible to liquefaction, than angular grained soils. Required time to trigger liquefaction increased with fines content and depth of the soil sedimentation. Liquefaction resistance of each tested sand decreased from 1st to the 2nd shaking, despite increase in relative density. Relative density values increased with each shake. Despite the increase in relative density, liquefaction resistance decreased. Relative density values have decreased, when fines content increased, but despite decreased in relative density, liquefaction resistance increased. Ground settlement values after the shaking was more than during the shaking. Ground settlement values have increased with fines content of the soil model.