Rektörlüğe Bağlı Birimler

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    Dams in the wake-up call of the 2023 Türkiye earthquake sequence: Insights from observed damages, risk assessment, and monitoring
    (Elsevier, 2024-01) Hariri-Ardebili, Mohammad Amin; Tosun, Hasan
    On February 6, 2023, Türkiye experienced a significant earthquake with a magnitude of 𝑀𝑤 7.81, followed by four additional earthquakes throughout the day, measuring 𝑀𝑤 5.8 and above, including one with a 𝑀𝑤 7.5. As a result, over 100 dams in the region experienced low to high seismic loads. The impact of these seismic events resulted in a range of damages to dams, varying from light to severe. The authors participated in several post-earthquake reconnaissance missions to collect perishable data regarding the damage. This paper is threefold: First, it explores the seismic performance and observed damage in 17 dams (majority embankments) based on data collected from the field. During the seismic activity, embankment dams underwent failure modes such as strength deterioration, yielding, settlement, tension crack formation, as well as sliding along planar or circular surfaces. Second, the paper offers an updated seismic risk analysis for ten selective damaged dams in the regions. Total risk factors are quantified using two different methods. The results show that the majority of the studied dams are classified as high and very high-risk dams. Third, the paper evaluates 11 other dams in the region that were equipped with sensors for monitoring the ground motions. The recorded acceleration at the crest and the abutment are further used to investigate the amount of amplification based on transfer functions. These recordings will be crucial for subsequent model calibration and system identification. Overall, the paper’s objective is to contribute to sharing post-earthquake reconnaissance mission information and to establish the groundwork for in-depth numerical analyses and quantitative risk assessments of dams located in seismically vulnerable areas.
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    Effect of stress conditions on concentrated leak erosion resistant of fine-grained soils with different characteristics
    (Springer, 2024-08) Topçu, Sadettin; Savaş, Hasan; Tosun, Hasan
    Internal erosion is one of the most important factors that cause earth structures that retain water, such as embankment dams, to collapse. Concentrated leak erosion, one of the forms of internal erosion, occurs in cracked fine-grained soils and pressurized flow conditions. To evaluate the concentrated leak erosion risk of cracks/voids, it is necessary to ascertain the erosion resistance of these materials. The erosion rate and critical shear stresses determine internal erosion resistance in concentrated leak erosion. This study determined soil’s concentrated leak erosion resistance using test equipment that allowed the flow to pass through a hole with stress-free (no loading), anisotropic-compression stress, anisotropic-expansion stress, and isotropic stress conditions. The stresses that developed in the samples’ hole wall where erosion occurred were determined with numerical modeling as pre-experimental stress conditions. The experiments were performed under a single hydraulic head on four selected cohesive soils with different erosion sensitivity. Time-dependent flow rates obtained from the test system can be used to determine hydraulic parameters, such as energy grade lines, with the help of basic theorems of pipe hydraulics in theoretical hydraulic models. Moreover, the erosion rates were quantitatively determined using the continuity equation, while critical shear stresses were qualitatively compared for concentrated leak erosion developed by the dispersion mechanism. As a result of the experiments, stress conditions influence the concentrated leak erosion resistance in the soil samples with dispersive erosion. Moreover, the shear strength in the Mohr–Coulomb hypothesis can explain the erosion resistance in these soils under stress conditions depending on the sand/clay ratio.