Department of Civil Engineering
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Browsing Department of Civil Engineering by Author "Akış, Ebru"
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Item AN INVESTIGATION FOR THE RESIDUAL STRENGTH OF REMOULDED CLAY SPECIMENS RECOVERED FROM ORDUKÖY LANDSLIDE IN NORTHERN TURKEY(2017-01-07) Mekael, Ahmad; Akış, Ebru; Yılmaz, M. TolgaLandslides are among the frequent natural disasters in Turkey. In order to take effective remedial measures for active landslides, their mechanism should be accurately modeled for analyses. The uncertainty regarding the residual shear strength on failure plane is a significant issue to be solved for a reliable model. The residual shear strength can be measured by multi-reversal direct shear tests and ring shear tests in laboratories, and by vane tests on the sites of landslides. In the scope of this study, the residual shear strength of remoulded clay specimens recovered from a landslide in Sinop Province of Turkey is investigated by the multi-reversal direct shear test results. Atterberg limits for clay specimens are LL=64, PI=43 and clay fraction in the specimens is 59.5%. A big consolidation box has been built to reduce the total time necessary for consolidation before shearing, and to solve the issues relevant to squeezing the very soft remoulded clay in direct shear box, and to prepare uniform specimens for testing. Multi-reversal direct shear tests on consolidated specimens were run with shearing rates ranging from 0.0007 mm/min to 0.024 mm/min. The number of shearing cycles was ranging from 5 to 9. The set of normal stress included the figures 51.1, 102.2, and 204.4 kPa. The rate effect on residual shear strength was observed in the tests, and a number of preliminary observations on this effect was explained for consideration in future testing studies. In this study, the residual friction angle is supposed to be the secant friction angle (c=0) during mobilization of residual strength. The secant friction angle is estimated to be ranging from 11.7° to 13.2° . The limitations of this study are criticized. The estimated range of angle of residual strength was observed to be reasonably consistent with empirical relationships presented in literature and with the figures estimated according to the limit-equilibrium analyses of the landslide.Item AN INVESTIGATION OF DRAINED SHEAR STRENGTH OF OVERCONSOLIDATED HIGH PLASTICITY CLAYS(2022-01-13) Yaşar, İrem; Akış, Ebru; Yılmaz, M. TolgaIn the design and analyses of geotechnical structures, drained or undrained shear strength parameters of the clays are used depending on the drainage conditions. In short term, such as during rapid construction of embankments or foundation on clays or at the end of construction of excavation in clay the undrained shear strength parameters should be used. Whereas, when the excess pore water pressure is completely dissipated, the analysis can be carried out in terms of effective stresses. Therefore, the drained shear parameters are used in the design of foundations, retaining structures and slope stability analyses. In this thesis, experiments are conducted to investigate the drained shear strength parameters of remolded high plastic clays (CH) which are collected from the Atılım University campus. Atterberg limits and the clay fraction of the soil samples are determined as LL= 62%, PI= 36% and CF=46%, respectively. In this research, there are two different experimental studies to investigate the shear strength parameters by using direct shear tests, since then they are the most widely used laboratory tests to determine these parameters. In the first test series, the drying effect on the peak and residual shear strength parameters is investigated by using multi-reversal direct shear tests with a newly developed resistance system. In the first part of these tests, a normally consolidated high plastic clay sample at the liquid limit is prepared and multireversal direct shear tests are conducted at 0.035mm/min shearing rate under 300 kPa. The soil sample is heated to dry out before shearing. The peak and residual shear strength determined by tests on wet samples are compared with those of dry samples. It is seen that the water content effect on the peak and residual shear strength that have been already reported in the literature is observed in the first multi-reversal direct shear tests. A decrease in water content results in an increase in peak and residual strength values. In the second part, multi-reversal tests under 200 kPa normal stress are performed on a lightly overconsolidated (OCR=1.5) soil sample at a slower rate (0.0035mm/min) but after residual strength is reached, the soil specimen heated and sheared one more time to investigate the change in residual shear strength. It is seen that the decrease in water content of the soil that has been reached to the residual state does not affect the residual shear strength of the soil. In the second test series, drained direct shear tests are performed on soil samples having different OCR values to predict an empirical correlation between drained shear strength of overconsolidated and normally consolidated clays. The direct shear tests are conducted on soil samples that are prepared at OCR=1, 2, 4 and 7 under normal stresses 50 kPa, 100 kPa and 200 kPa and the shearing rate of these tests are set as to 0.0018mm/min. The test results are evaluated and the prediction equation is presented.Item AN INVESTIGATION ON THE MECHANICAL PROPERTIES AND BEHAVIOR OF EXPANDED POLYSTYRENE (EPS) GEOFOAM(2022-01-24) Güven, Güral; Akış, EbruExpanded polystyrene (EPS) geofoam blocks have been used for various purposes in civil engineering applications. The initial elastic modulus and compressive strength are considered to be the two most significant engineering properties of these materials for modeling and design. In the first part of this study, unconfined compression tests on EPS geofoam samples having different shapes (cubic or disc), dimensions (50 mm, 100 mm and 300 mm for cubic samples and diameters of 50 mm, 65 mm and 100 mm with different aspect ratios for disc samples) and densities (14, 22 and 26 kg/m3 ) are performed to determine initial elastic modulus and compressive strength. 356 unconfined compression tests with different loading rates are performed. In the second part, 294 of the test results obtained in the first part are used to predict the initial elastic modulus and the compressive strength of EPS geofoam by using regression analysis. Predicted strength values at 5% strain (σ5) and 10% strain (σ10) were excellently correlated with real values by higher than 0.96 R2 values for both cubic and disc samples. The R2 value is 0.94 for initial modulus of elasticity (𝐸𝑖 ), strength values at 1% strain (σ1) for cubic samples whereas the figure is 0.76 for disc samples. To predict reliable 𝐸𝑖 and σ1 values for disc specimens between effecting parameters, a previously developed ANN (artificial neural network) algorithm is used. The rest of the test results are used to compare the results of predicted figures from the regression analyses and ANN algorithm. ANN algorithm successfully predicted the initial modulus of elasticity (𝐸𝑖 ), the strength values at 1% strain (σ1) outputs with R2 values of 0.9874 and 0.9876 respectively.