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    INVESTIGATION OF ACTIVE FAILURE SURFACES OCCURRING BEHIND THE T TYPE CANTILEVER RETAINING WALL
    (Necip Fazıl YILMAZ, 2021) Kamiloğlu, Hakan Alper; Yılmaz, Fatih; Şadoğlu, Erol
    Determination of lateral earth pressure plays a vital role in retaining wall design. Failure surfaces are very effective in active lateral earth pressure acting on cantilever retaining walls. Calculations of lateral earth thrusts vary for two different cases, namely short heel or long heel, based on the intersection of T type cantilever wall and failure surface. In this study, the effect of heel length on an active failure mechanism was examined with numerical simulation based on FEM. The results of the numerical analyses were compared with the results of small-scale model tests and an analytical method. In comparison, the inclination angle of active failure surfaces was taken into account. An earth thrust maximization code suggested in the literature was used to determine failure surface inclination angles analytically. In order to determine failure inclination experimentally, results of small scale tests were used. In the tests, failure surfaces were determined using particle image velocimetry technique (PIV). Numerical analysis was performed using commercially available finite element program Plaxis 2D. The same material properties are used in all numerical models. As a result of the study short heel-long heel cases and effective parameters on the inclination angles of the failure surfaces are explained elaborately.
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    Investigation of Durability Performance of High Plasticity Silty Soil Improved with Alkali Activated Fly Ash and Polypropylene Fiber
    (2025) Kamiloğlu, Hakan Alper; Kurucu, Kutluhan; Durak, Muhammet Oğuz
    This study investigates the durability performance of high-plasticity silty soil stabilized with alkali-activated fly ash and reinforced with polypropylene fibers. Unlike conventional practice, the effect of different lengths of fiber reinforcement combinations on durability was investigated in this study. The study combines alkali activation technology with hybrid fiber reinforcement, utilizing a mixture of 3 mm and 12 mm length polypropylene fibers. While traditional methods usually focus on wetting-drying or freeze-thaw cycles for durability assessment, the durability effect was achieved in this study through wetting tests involving long saturation periods. Within the scope of the study, specimen residues obtained from three-point bending tests were used as test specimens. The study investigated the effects of reinforcement content and hybrid reinforcement effect parameters on durability performance. Key findings of the study include: (1) The increase in sodium silicate content increased the durability performance of the material. (2) Both 3 mm and 12 mm length fiber addition increased the durability performance. (3) Length hybrid fiber combinations showed better durability performance compared to single length fiber reinforcements.
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    Numerical Analysis of Active Earth Pressures on Various Types of Retaining Walls
    (2019) Kamiloğlu, Hakan Alper; Şadoğlu, Erol; Yılmaz, Mehmet Fatih
    Lateral earth pressure distribution is crucial in retaining structure design. In most studies, active earth pressuredistribution acting on the retaining structure is supposed as nonlinear. Despite there are many studies aboutearth pressure distribution, there are limited number of studies considering effect of wall geometry on lateralearth pressure distribution. In this study, it is aimed to examine effect of wall geometry on active failure surfacesand lateral earth pressure distribution. Thus, active failure surface and active lateral earth pressure distributionof various types of retaining wall were examined numerically. Within scope of the analysis a gravity retainingwall with various inclinations, inverted T type cantilever retaining wall and gravity wall with various heellengths were considered. The effect of wall inclination and heel length on failure mechanism and lateral earthpressure distribution was studied. As a result of the study it is shown that lateral earth pressure distributionvaries based on wall type. Additionally, short heel and long heel cases are effective on earth pressuredistribution.
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    Optimization and Mechanical Performance of Alkali-Activated Bottom Ash and Polypropylene Fiber in Deep Mixing Columns
    (Manisa Celal Bayar University, 2025) Yılmaz, Fatih; Avlayan, Büşra; Kamiloğlu, Hakan Alper
    Deep mixing columns (DMC) are one of the widely used soil improvement methods in cohesive and cohesionless soils. Cement and lime are predominantly used as conventional binders in DMC grout. Due to high CO2 emissions from conventional binders, the feasibility of using alkali-activated binders as DMC grout is being investigated. This study was conducted in three main stages. In the first stage, the proportions of bottom ash and activator (mixture of 10M NaOH and Na2SiO3) were optimized to achieve the highest UCS value using response surface methodology (RSM). In the second stage, the influence of polypropylene fiber content was examined in detail by incorporating varying amounts of fibers into the optimized binder-activator mixture to determine the optimal fiber content. Since DMC are fully buried, they are cured in the soil media. In this case, the soil temperature, which varies along the depth of the soil, also becomes the curing temperature of the DCM. Due to climate, soil condition and thermodynamic based parameters, curing temperature of the DMC varies throughout the soil depth. Therefore, in the third stage, the effect of curing temperature on the mechanical properties of the stabilized samples was evaluated under different temperatures. Results of the study revealed optimal UCS values with AAB content of 0.3-0.5 and activator content of 0.45-0.5. Polypropylene fiber reinforcement further improved strength, reaching an optimum at 1.50-1.75% content. Curing temperature played a significant role, with UCS and modulus of elasticity increasing up to 30 °C, indicating the importance of considering environmental factors in DMC design. These findings suggest that the optimized mixture has the potential to replace conventional cement-based binders in DMCs, offering a more sustainable solution with lower carbon emissions. Furthermore, the observed influence of curing temperature highlights the need to account for subsurface thermal variations when designing DMCs, as these factors significantly affect strength gain and long-term performance.
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    Optimization Of Cantilever Retaining Wall Design Using Improved Teaching-Learning-Based Optimization Algorithms
    (2024) Tayfur, Bilal; Kamiloğlu, Hakan Alper
    Retaining structures play a crucial role in geotechnical engineering to support soil levels, prevent slope failure, and create flat surfaces for construction. Designing these structures involves optimizing internal and external stability while minimizing material usage and cost. This study focused on optimizing reinforced concrete cantilever retaining walls using the Teaching-Learning Based Optimization (TLBO) algorithm and an improved version (I-TLBO) with agents. In the context of the study, geometric-structural design variables, geotechnical -structural constraints, and optimization processes were examined. Minimizing weight and minimizing cost of the wall were the objectives considered in the cantilever retaining wall design process. The optimization results were compared with other algorithms in the literature, such as genetic algorithms, evolutionary strategies, and particle swarm optimization. The improved TLBO algorithm demonstrated superior performance, achieved lower design dimensions, and reduced costs. It provided more efficient solutions that pushed design constraints closer to their limits, resulting in a cost-effective and structurally sound cantilever retaining wall design. As a result of the study, the I-TLBO algorithm was found to be more cost and weight-effective than other methods in the optimization of cantilever retaining wall design.
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    Optimization, Characterization, and Carbon Footprint Analysis of Alkali Activated Waste Tuff and Fly Ash Mixtures for Deep Mixed Columns
    (Springer Science and Business Media Deutschland GmbH, 2024) Kamiloğlu, Hakan Alper; Yilmaz, Fatih
    Deep soil mixing (DSM) applications are one of the widely known soil stabilization techniques which can be applied to a wide range of soil types. Cement and lime are the major materials used as binders for DSM applications. However, as conventional binders lead to emit a large amount of CO2 during production, eco-friendly binders suitable for DSM applications have become prominent. Alkali-activated materials are good alternatives to conventional binders. This study was intended to investigate the usability of zeolite rich tuff wastes as an alkali-activated binder in DSM columns. Within this scope, the waste tuff and C-type fly ash mixture were used as an alkali-activated binder, and 10 M NaOH solution was used as an activator. Response surface methodology (RSM) was employed in experimental design to determine optimum components to obtain maximum unconfined compression strength and investigate the interaction between stabilization agents. From the RSM analysis the optimum ratios of activator (X1), waste tuff (X2), and precursor (X3) were determined as; X1 = 0.251, X2 = 0.548, and X3 = 0.538 for maximum UCS. UCS, mineralogical and microstructural characterization (XRF, XRD, SEM, EDX, FTIR) was performed for the DSM samples prepared considering the optimized components. It was determined that the UCS values of the 3, 7, and 28-day cured samples stabilized by considering the optimum values gave UCS values approximately 3 to 5 times higher than the lower limit values recommended by FHWA. As a result of mineralogical and microstructural investigation, the reason for the strength increase in the samples can be attributed to the formation of geopolymeric gel between the soil particles by tuff waste and fly ash activated with alkaline activator. Carbon footprint analyses were performed for 1m3 DSM columns produced with alkali-activated binders and ordinary Portland cement (OPC). From the analyses it was seen that the carbon footprint of the DSM column produced using alkali activated binders is lower than that of the DSM column obtained with OPC. After the general evaluation of the study, it is seen that the hypothesis that waste tuff can be used as environmentally safe alkali-activated binders instead of traditional binders is supported. © The Author(s), under exclusive licence to Shiraz University 2024.
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    Optimization, Characterization, and Carbon Footprint Analysis of Alkali Activated Waste Tuff and Fly Ash Mixtures for Deep Mixed Columns
    (Springer Science and Business Media Deutschland GmbH, 2024) Kamiloğlu, Hakan Alper; Yilmaz, Fatih
    Deep soil mixing (DSM) applications are one of the widely known soil stabilization techniques which can be applied to a wide range of soil types. Cement and lime are the major materials used as binders for DSM applications. However, as conventional binders lead to emit a large amount of CO2 during production, eco-friendly binders suitable for DSM applications have become prominent. Alkali-activated materials are good alternatives to conventional binders. This study was intended to investigate the usability of zeolite rich tuff wastes as an alkali-activated binder in DSM columns. Within this scope, the waste tuff and C-type fly ash mixture were used as an alkali-activated binder, and 10 M NaOH solution was used as an activator. Response surface methodology (RSM) was employed in experimental design to determine optimum components to obtain maximum unconfined compression strength and investigate the interaction between stabilization agents. From the RSM analysis the optimum ratios of activator (X1), waste tuff (X2), and precursor (X3) were determined as; X1 = 0.251, X2 = 0.548, and X3 = 0.538 for maximum UCS. UCS, mineralogical and microstructural characterization (XRF, XRD, SEM, EDX, FTIR) was performed for the DSM samples prepared considering the optimized components. It was determined that the UCS values of the 3, 7, and 28-day cured samples stabilized by considering the optimum values gave UCS values approximately 3 to 5 times higher than the lower limit values recommended by FHWA. As a result of mineralogical and microstructural investigation, the reason for the strength increase in the samples can be attributed to the formation of geopolymeric gel between the soil particles by tuff waste and fly ash activated with alkaline activator. Carbon footprint analyses were performed for 1m3 DSM columns produced with alkali-activated binders and ordinary Portland cement (OPC). From the analyses it was seen that the carbon footprint of the DSM column produced using alkali activated binders is lower than that of the DSM column obtained with OPC. After the general evaluation of the study, it is seen that the hypothesis that waste tuff can be used as environmentally safe alkali-activated binders instead of traditional binders is supported. © The Author(s), under exclusive licence to Shiraz University 2024.