Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Effect of Stone Column Soil Improvement on Liquefaction Resistance: Field and Numerical Study(01. Izmir Institute of Technology, 2023) Budak, Merve; Ecemiş Zeren, NurhanThis study aims to understand how effective the group of stone columns is in the liquefaction mitigation of loose silty sands. Stone columns have drainage properties that help dissipate pore water pressure under cyclic loading, so the technique is used to improve the behavior of the soil under cyclic loadings, such as earthquake loading. Several analytical, experimental, and numerical studies on the liquefaction mitigation of soils by stone columns are available in the literature. Analytical methods are usually directly or indirectly based on the results of field tests that reveal the effects of stone columns. More research is needed to identify the reduction of liquefaction by stone columns, as several variables control the percentage of soil liquefaction improvement in the field. In this study, the behavior of the group of stone columns is modeled by the finite difference method (FDM), where the field test data is used as an input. The pre and post-improvement soil data used in the analyses were obtained from cone penetration tests (CPT) performed in the field before and after the construction of the stone columns using the vibroflotation (wet bottom-feed) method. Then, the earthquake loading has been applied to the unimproved and improved soil models by the stone columns. Finally, under the earthquake loading, the percentage of the liquefaction resistance increase and the settlement of the loose silty sand under structural load after stone column construction is investigated.Master Thesis Numerical Modeling of the Filter Sand Performance in Embankment Dam Under Static and Dynamic Conditions(01. Izmir Institute of Technology, 2023) Karaoğlu, Aybüke; Ecemiş Zeren, NurhanThe filter material in embankment dams is a crucial part of the dam due to protecting the core material (usually clay) against internal erosion. Internal erosion is defined as the transportation of core material particles to the filter material by seepage flow. It is the main reason for the deformation and loss of resistance in the body and foundation of a dam. Therefore, it is a serious threat risk to embankment dams. To prevent internal erosion, it is necessary to accurately evaluate the interaction between water-filter material-core material during the dam's design and operation stages. A suitable filter material should be able to control and block cracks that can form in the core material. Terzaghi (1925) did the first research on filter material and proposed a criterion based on the particle size of a clay. Another detailed study was conducted by Sherard et al. (1989) who developed an experiment called No Erosion Filter Test (NEF Test) to comprehend the relationship between filter and core materials. NEF Test is seen as the most proper method to determine the critical filter which leans on the impermeable core material in the downstream side of an embankment dam. In the NEF test, the most severe condition that can occur is represented as an erosive leak from the core material to the filter material. Within the scope of this study, the internal erosion of the backfill used in the dam is studied through outflow rate and deformations in the base sample (clay). First, the samples taken from two embankment dams in Izmir (Kalabak Dam and Rahman Dam) were brought to the geotechnical laboratory of Izmir Institute of Technology (IZTECH), and the filter material was mixed with fine materials (silt) in different contents. A series of NEF Tests were performed in the IZTECH-geotechnical laboratory on the filter and core samples of Kalabak Dam within a TUBITAK Project No. 221M071 (Ecemis, 2023). Then, the performed NEF Tests were modeled by the finite difference method (FDM) using the Itasca-FLAC3D software. Finally, the outcomes of the numerical models were compared to experimental results. Numerical models had a good agreement to decide whether filter sand performance is successful or not.Master Thesis Effect of Fines and Ground Acceleration on Liquefaction Resistance of Silty Sand: Numerical Study(Izmir Institute of Technology, 2022) Tozburun, Batuhan; Ecemiş Zeren, NurhanLiquefaction is a phenomenon that damages structures that have not been adequately studied during the design process. While improving the performance of the buildings under dynamic loading conditions, it is essential to evaluate the liquefaction behavior of soils under the dynamic load. In this thesis, the constitutive soil model (UBCSand Model), which can simulate liquefaction, is used within the finite difference methods (FDM). First, results are compared with the laboratory test results to verify numerical liquefaction simulations. The physical and mechanical tests performed at Izmir Institute of Technology (IZTECH) are used as an input for the soil model. Then, a series of constant volume cyclic direct simple shear results (CDSS) tests performed for the same silty sands were used to verify the numerical study (Tutuncu, 2021 and Monkul, 2021). CDSS tests were performed on mixtures of clean sands and three non-plastic silts at different contents of 0%, 5%, 15%, and 35% allowing for observing the liquefaction response of silty sands of different grades (Monkul, 2021). The laboratory tests performed at Yeditepe University and Izmir Institute of Technology were combined to study the effect of fines content and relative density on cyclic liquefaction resistance of silty sands. The aim of this thesis is to perform a numerical model to evaluate the effect of fines content (FC), ground acceleration (amax) and relative density (Dr) on liquefaction resistance. The FDM model gives similar results to laboratory test results. Hence, the model can be used to assess the liquefaction with different soil models and conditions.Master Thesis Performance of Sand Granulated Rubber Mixture for Soil Stabilization Using Discrete Element Method (dem)(Izmir Institute of Technology, 2022) Kadekeshova, Kuralay; Ecemiş Zeren, NurhanThe results of a detailed analysis of the capability of numerical approach Discrete Element Method (DEM) to replicate a physical model of a sheet pile foundation in dry soil under static loads are presented in this study. Accordingly, the DEM software Particle Flow Code 2-Dimensional (ITASCA, 2019) is used to model experimental tests. Numerical model of direct shear test on clean sand and sand mixed with 10% granulated rubber has been done to calibrate the micromechanical parameters of the granular materials, such as sand and rubber particles. The particle sizes, density, interparticle friction coefficient, and contact stiffness of the discrete elements were determined and used in DEM simulations of sheet pile foundation. A total of four DEM models of the sheet pile foundation with different sand-rubber mixture backfill area were tested and analyzed in PFC2D. The loading process speed, contact stiffnesses, and porosity of the system had a significant impact on the deformation parameters of the sheet pile and lateral pressure distribution of the sand-rubber mix backfill. In this study two measurement methods were investigated. First, the measuring particles of the sheet pile particles were used, whereas the second, the measuring circles were placed behind the sheet pile foundation. The measurement circles proposed by (ITASCA, 2019) were suitable for the DEM model. Numerical outcomes showed a relative good match with the physical model. Finally, the ability of the PFC2D code as a discrete element approach in modelling of cohesionless granular material and sheet pile foundation is confirmed in this work.Master Thesis Influence of Soil on Cone Penetration Resistance-Shear Wave Velocity Correlation(Izmir Institute of Technology, 2022) Örücü, Murat; Ecemiş Zeren, NurhanMany researchers proposed correlations between cone penetration resistance (qc) and shear wave velocity (Vs). The researchers used the datasets they obtained by performing laboratory or field tests while developing their correlations. The qc measurements were made with CPT test and Vs measurements were made with in-situ tests (SCPT, DHT, CHT). The proposed correlations were very different from each other. The existing correlations between qc and Vs are given in two ways: The soil type-dependent correlations and different correlations for different soil types. The soil type-dependent correlations were limited and also there is no change depending on fines content . Therefore, it would be useful to determine a correlation based on soil type with soils with different fines content. In this study, CPT and SCPT tests were performed in the getechnical laboratory of IZTECH to investigate the influence of soil type on qc-Vs correlation. Tests were performed on clean sand and sand - non-plastic silt mixtures having 5%, 15%, and 35% fines content at different relative densities inside the soil box. CPT profiles and Vs values were obtained to develop a relationship between Vs, and qc based on soil type index (Ic). The Ic values were found using CPT-based approaches found in the literature. A new soil type-dependent correlation to predict the Vs of soils from qc is presented in this study. The new equation was compared with existing correlations. The equation is useful to estimate Vs from CPT measurements for all soil types with different fines content.Master Thesis Field Investigation-Effect of Coefficient of Consolidation and Relative Density on Cone Penetration Resistance(01. Izmir Institute of Technology, 2021) Taneri, Hazal; Ecemiş Zeren, NurhanCoefficient of consolidation (ch) and relative density (Dr) are major parameters to explain soil behavior of silty sands. In this study, it was aimed to compare the effects of ch and Dr of drained, partially drained and undrained soils on cone penetration resistance and excess pore water pressure. Several field tests; piezocone penetration test (CPTu), standard penetration test (SPT), pore pressure dissipation test (PPDT) and direct push permeability test (DPPT) were conducted on the Northern side of the Izmir Gulf at 20 different locations in 2013 by Ecemis et al. At each location between Cigli and Karsiyaka tests were performed 2.6 m apart from each other. The cone resistance qc, the frictional resistance fs, and pore water pressure behind cone u2 were obtained from CPTu tests. During the investigation, the effect of ch obtained from PPDT and DPPT which were conducted at the same depths for each borehole could be examined. SPT tests were used to estimate the Dr of the soil. The disturbed soil samples collected from the boreholes were classified as poorly graded clean sand (SP) to silty sand (SM) and clayey sand (SC). Results showed that qc decreased and u2 increased as the non-dimensional penetration rate (T= vd/ch) increased at the same Dr. From drained to undrained penetration, limit values for the T were determined, and it was seen that T and Dr influenced qc and u2 from medium dense to loose silty sands. Also, it was observed that u2 will be negative for denser silty sands.Master Thesis Investigation on the Liquefaction Potential of Sand-Granulated Rubber Mixture That Used Around the Buried Pipes: Numerical Modeling and Developing(01. Izmir Institute of Technology, 2021) Valizadeh, Hadi; Ecemiş Zeren, NurhanRecently, the sand-granulated rubber mixture has been reported as a new soil improvement method that can be applied as a liquefaction mitigation filling material around the buried pipes. This study performed numerical modeling of liquefaction potential of tire-derived granulated rubber–sand mixture used around the buried pipes by the FLAC 2D software. The effects of pipe size, burial depth, and shaking intensity on the pipe uplift and the liquefaction potential of the sand-tire derived granulated rubber mixture placed around the buried pipes were investigated using the finite difference method. Furthermore, UBCSAND advanced soil constitutive model was used for liquefaction analysis. First, the result of 1-g shaking table tests was utilized for the verification of the numerical analysis. Comparing the numerical results and the experimental measurements showed that the numerical simulation using the UBCSAND constitutive model could accurately estimate the liquefaction-induced uplift of the buried pipes as well as the related failure. Then, a parametric study was conducted to investigate the effects of the pipe diameter, pipe depth, and the maximum acceleration on pipe uplift and liquefaction potential when the sand-granulated rubber mixture was placed as the filling material. Eventually, an analytical formula was proposed to estimate the liquefaction-induced uplift of buried pipes, and the soil failure mode was categorized according to the pipe's burial depth.Master Thesis Effect of Fines Content on Cpt Resistance in Silty Sands(01. Izmir Institute of Technology, 2021) Arık, Mustafa Sezer; Ecemiş Zeren, NurhanThe effect of fines content on cone penetration resistance and excess pore water pressure is not entirely known yet. In this study, CPTu, SCPT, and DPPT tests in a fixed wall laminar box were carried out to understand the effect of fines content with different relative densities on cone penetration resistance and excess pore water pressure in clean sand and sand with 5, 15, and 35 percent silty. This study was investigated by using the normalized penetration rate. The effect of normalized penetration rate accounted with penetration rate and coefficient of consolidation on drainage conditions and the value of transition from partially drained to drained conditions were investigated. According to the experimental data results, the effect of fines content on the coefficient of volume compressibility is minimal. However, as the fines content increase, the permeability and the coefficient of consolidation decrease considerably. The normalized cone penetration resistance decreases when the fines content increases in clean sand and silty sands at the same relative densities. When the relationship between normalized penetration rate and normalized cone penetration resistance is examined instead of only the fines at the same relative densities, the normalized cone penetration resistance decreased with the increasing normalized penetration rate. Due to a decrease in the coefficient of consolidation or an increase in the penetration rate, silty sands have a longer dissipation time of excess pore water pressure than clean sand. Hence, the clean sand remains drained, and the silty sands remain partially drained.Master Thesis Numerical Modeling of Jet Grouting Cells To Reduce Liquefaction(Izmir Institute of Technology, 2019) Gürbüz, Çağdaş; Ecemiş Zeren, NurhanThe importance of the preservation of historical and culturally important buildings is essential nowadays. While improving the performance of the buildings under dynamic loadings, it is essential to evaluate and improve the subsoil conditions. It is evident, that strengthening of the building will not provide the desired performance, if serious ground problems such as liquefaction are not eliminated during earthquake loading. In this study, liquefaction evaluation of the foundation soil of a historical building (Vali Konagi), which is in the Konak district of İzmir province, has been carried out. The simplified liquefaction assessment results based on the standard penetration tests showed that under 0.45g loading, the liquefaction problem could be observed. Therefore, soil improvement is necessary for the upper profile beneath this historical building. The jet grout cells, which is a new method were suggested as a soil improvement technique against the liquefaction of the soil below the building. The parameters related to the jet grout cells were determined, and the improved soil status was analyzed. The numerical analyses of the liquefaction investigation at unimproved and improved soil were compared by finite difference program FLAC-2D. The constitutive model (UBCSand), which can simulate liquefaction was used in the program. As a result, it is observed that; by using jet grout cells liquefaction was not triggered and deformations were kept under control.Master Thesis A Case Study on Settlement Analysis of Geothermal Power Plant Foundation(01. Izmir Institute of Technology, 2018) Elmas, Hakan; Ecemiş Zeren, NurhanFoundation settlement criteria are highly sensisitive for geothermal power plants. In geotechnical literature there are several settlement analyses which can be done by using elastic approaches, in-situ test results or numerical methods. Unfortunately, all these methods cannot give close results with each other. As a result, the unrepresentative analyses influence the safety, economy and time of the projects. In this study, the settlement of the geothermal power plant located in Aydın / İncirliova which constructed on a raft foundation was investigated. According to soil investigations, the raft foundation is located on multilayer soil profile and a compacted high qualified fill layer is placed under the raft foundation. Soil parameters were obtained from in-situ tests (standard penetration tests, cone penetration tests, pressuremeter tests and plate load test and) and laboratory experiments. Settlement results were obtained by 1D stress – strain analyses and 3D continuum numerical analyses (Hardening Soil Model with Small Strain Stiffness and Mohr Coulomb Soil Model) using the commercially available Settle 3D and Plaxis 3D software, respectively. The results of these analysis were also compared with the field monitoring data. The results show that Hardening Soil Model with Small Strain Stiffness gave more accurate result than other models due to the representation of real soil behavior, obtaining non-uniform stress distribution of foundation and obtaining effective stress depth accurately for settlement.