Sami Oguzhan Akbas

Turkey is located on an active seismic belt, making the accurate determination of soil properties and earthquake effects essential for safe and reliable structural design. This study investigates the influence of ground improvement on the dynamic behavior of the soil at the construction site of the 950-bed Aydın City Hospital. Evaluations were carried out in terms of the dominant period, local site class and spectral characteristics to assess the effectiveness of the improvement applications. For this purpose, field tests conducted before the improvement were repeated afterward and the obtained data were compared. Local site classes were determined for both unimproved and improved soil conditions based on the relevant seismic code provisions. Furthermore, using site-specific data, nonlinear time-history analyses were performed and site-specific response spectra were obtained for 11 earthquake records at DD-1 and DD-2 seismic hazard levels (return periods of 475 and 2475 years). These spectra were then compared with the corresponding design spectra. The analyses revealed that ground improvement significantly affects not only the bearing capacity and liquefaction potential but also the dynamic behavior, dominant period and local site class of the soil.

The goal of the this study is to investigate the applicability of the teaching-learning based optimization (TLBO) algorithm for modeling seepage in embankment dams. The input parameters selected for the models to be built are the values of permeability (ks), van Genuchten's suitability parameters α and n, whose effect on seepage has been investigated over the years due to their uncertainties. The validity of the TLBO was compared with that of conventional regression analysis (CRA) methods. Both methods were utilized with different regression forms. The parameters chosen as input are modeled as random variables with a log-normal distribution, and total discharge (Q) was obtained. Four statistical indices, that is, root mean square error, mean absolute error, average relative error and coefficient of determination, were used to evaluate the performance of the models. The equations obtained using TLBO algorithms can predict the total discharge in embankment dams better than CRA. In addition, the reliability of TLBO has been demonstrated by conducting analyses using the outputs of CRA as a benchmark.

Dolgu barajlarda suyun barajın memba kısmından mansap kısmına doğru sürekli ve engellenemeyen hareketi sızma olarak tanımlanır. Tasarım aşamasında bu hareketin belirli bir mertebenin altında tutulması hedeflenir. Bu hedef doğrultusunda sızmanın doğru tahmin edilebilmesi için konu üzerinde çok sayıda deneysel ve sayısal çalışma yapılmıştır. Son yıllarda hesaplardaki belirsizliklerin azaltılması amacı ile zemindeki değişkenliklerin de dikkate alındığı ve sonlu elemanlar yönteminin sıklıkla kullanıldığı olasılıksal analizler de gerçekleştirilmeye başlanmıştır. Bu kapsamda, mevcut çalışmada kil çekirdek malzemesinin permeabilite değerindeki belirsizlikler göz önünde bulundurularak sonlu elemanlar yöntemi ile gerçekleştirilen olasılıksal sızma analizlerinin, farklı çekirdek şev eğimlerine sahip iki adet kil çekirdekli dolgu baraj üzerinde bir uygulamasına ait sonuçlar sunulmaktadır. Öncelikle, kil çekirdeği oluşturan zemine ait permeabilite değerlerinin istatistiksel parametreleri belirlenmiş, Monte Carlo simülasyonları ile üretilen permeabiliteler PLAXIS 2D programında yapılan sızma analizlerinin girdileri olarak olarak kullanılmıştır. Aynı ortalama değerinde elde edilen iki modele ait sonuçlar birbirleriyle ve deterministik olarak elde edilen sonuçlarla kıyaslanmıştır. Analiz sonuçları, olasılıksal analizle deterministik yönteme daha düşük sızma değerleri elde edildiğini ortaya koymaktadır. Ayrıca zemin parametrelerine ait kabul edilen olasılıksal dağılım özelliklerinin sonuçlar üzerindeki etkisi açıkça görülmektedir.

This study aims to assess the accuracy and consistency of existing correlations between undrained shear strength (c_u) and modulus of volumetric compressibility (m_v) with SPT N value, and compression index (C_c) with index parameters for Turkish clays, with a specific focus on Ankara clay using laboratory testing of over 2500 high-quality undisturbed samples from 42 sites. A comparison of correlations for c_u using five different statistical variables indicates that no single method stands out as superior in terms of both accuracy and conservatism and that the quality of the tests in the database has a significant impact on the correlation performance. Even the most effective correlation for c_u appear insufficient for direct application in geotechnical design processes, given its low consistency characterized by coefficient of variations (COV) ranging between 50% and more than 100%. The widely used m_v estimates proposed by Stroud (1974) were found to be notably unconservative when applied to Turkish clays. Consequently, a new trendline, leveraging both SPT N value and Plasticity Index (PI), was introduced to address this discrepancy. Meanwhile, an examination of 283 high-quality undisturbed samples from Ankara Clay revealed existing correlations between initial void ratio (e₀) and compression index (C_c) to be conservative, yet consistently reliable. This underscores their suitability for routine or preliminary design applications. Notably, a newly derived correlation was proposed, which demonstrates equal applicability to the well-established Bowles (1979) equation.

Submarine pipelines have become integral for transporting resources and drinking water across large bodies. Therefore, ensuring the stability and reliability of these submarine pipelines is crucial. Incorporating climate change impacts into the design of marine structures is paramount to assure their lifetime safety and serviceability. Deterministic design methods may not fully consider the uncertainties and risks related to climate change compared to risk-based design models. The latter approach considers the future risks and uncertainties linked to climate and environmental changes, thus ensuring infrastructure sustainability. This study pioneers a Hybrid 3D Hydrodynamic Monte Carlo Simulation (HMCS) Model to improve the reliability-based design of submarine pipelines, incorporating the effects of climate change. Current design approaches may follow deterministic methods, which may not systematically account for climate change’s comprehensive uncertainties and risks. Similarly, traditional design codes often follow a deterministic approach, lacking in the comprehensive integration of dynamic environmental factors such as wind, waves, currents, and geotechnical conditions, and may not adequately handle the uncertainties, including the long-term effects of climate change. Nowadays, most countries are developing new design codes to modify the risk levels for climate change’s effects, such as sea-level rises, changes in precipitation, or changes in the frequency/intensity of winds/storms/waves in coastal and marine designs. Our model may help these efforts by integrating a comprehensive risk-based approach, utilizing a 3D hydrodynamic model to correlate diverse environmental factors through Monte Carlo Simulations (MCS). The hybrid model can promise the sustainability of marine infrastructure by adapting to future environmental changes and uncertainties. Including such advanced methodologies in the design, codes are encouraged to reinforce the resilience of maritime structures in the climate change era. The present design codes should inevitably be reviewed according to climate change effects, and the hybrid risk-based design model proposed in this research should be included in codes to ensure the reliability of maritime structures. The HMCS model represents a significant advancement over existing risk models by incorporating comprehensive environmental factors, utilizing advanced simulation techniques, and explicitly addressing the impacts of climate change. This innovative approach ensures the development of more resilient and sustainable maritime infrastructure capable of withstanding future environmental uncertainties.

This study explores the impact of including the vertical spatial variability in effective stress friction angle of clay on the probabilistic analysis of deep excavations. The proposed methodology is demonstrated and verified by conducting random finite element modeling (RFEM) of an instrumented deep excavation project situated in Ankara, Turkey. The excavation has a depth of 20 meters and is supported by six levels of pre-stressed ground anchors. To simulate the vertical spatial variability of effective stress friction angle in the clay, Monte Carlo simulation method and the random field theory are employed. The simulated parameters are then inserted into the finite element model via Python programming language to analyze the probabilistic distribution of lateral deflections and bending moments in the drilled shaft wall. The results obtained from the Monte Carlo simulations reveal that the incorporation and selected value of spatial variability significantly impacts the resulting lateral movements, bending moments, and the probability of failure of the system.

Evaluation of the reliability of deep excavation support systems requires the inclusion of the soil variability in conjunction with probabilistic analysis. This is often considered a complicated process; therefore, the method is usually not followed in routine engineering practice. Recent developments in finite element modelling now enable probabilistic analyses to be performed more conveniently. As an illustrative example, the case history of a 20 m-deep excavation supported by anchored drilled shafts in the Sogutozu district of Ankara was investigated. Experimental results indicate that saturated sand-gravel bands, which are common within Ankara Clay, have the potential to cause a significant decrease in the anchor capacity. Ergo the excavation performance, including structural capacity and wall lateral displacements, was evaluated taking into regard the probabilistic nature of the effect of these bands and the variability of the soil parameters. Back-analysis was performed and compared with inclinometer readings to examine the capability of the numerical model to simulate the field behaviour. Later, additional finite element analyses were carried out through Python scripting software to investigate the reliability of the excavation. Geotechnical parameters of the Ankara Clay produced by Monte Carlo simulation method were used in these analyses. The results were evaluated within the context of recommended acceptable reliability levels. The reliability of the system was determined to be relatively low when taking into account the adverse impact of sand and gravel bands.