Hüseyin Suha Aksoy

The present study evaluated the potential of waste glass fiber-reinforced polymer (wGFRP) as a soil reinforcement material for geotechnical applications. Laboratory model footing tests and large-scale direct shear tests were carried out on sandy soils prepared at three relative densities (Dr = 40%, 65%, and 85%) and reinforced with four wGFRP contents (0.5%, 0.75%, 1.0%, and 1.5%) to evaluate bearing capacity, settlement behavior, and shear strength characteristics. Environmental characterization and a performance-based economic assessment were also conducted to assess environmental compatibility and identify the optimum reinforcement content from engineering and economic perspectives. The results showed that wGFRP improved sand performance under all investigated conditions. Optimum performance was achieved at 0.75% wGFRP, where the ultimate bearing capacity increased by up to 92%, settlement decreased by up to 79.2%, and the internal friction angle increased by up to 6.2%. Environmental characterization indicated compatibility under the investigated laboratory conditions, with negligible trace-element release and no significant physicochemical, microstructural, or chemical degradation. The economically optimum reinforcement content depended on the selected engineering objective and the initial relative density. The findings indicate that wGFRP has strong potential as a sustainable, environmentally compatible, and cost-effective soil reinforcement material, offering a high-value reuse pathway in geotechnical applications.

While existing analytical methods provide solutions for calculating vertical pressures in soil, calculating lateral stresses remains a critical challenge. Therefore, experimentally measuring stress values is essential, considering the various factors influencing these stresses. This study investigates the lateral stress variations occurring beneath foundations placed on sandy soil and assesses the ultimate bearing capacity and settlement behavior of these foundations. Additional lateral stresses were measured beneath square shallow foundations on the sand with varying relative densities. The model tests were conducted in a square-sectioned sand tank. The results revealed that the lateral stress values tended to increase with both the foundation size and soil density, with this effect being most pronounced at a relative density of 90%. Furthermore, the lateral stresses decreased with increasing depth beneath the foundation for all foundation sizes. Loading tests were performed on square foundations of various sizes placed on sand prepared at different relative densities. A significant increase in the ultimate bearing capacity was noted as the foundation size and relative density of the soil increased. The measured lateral stresses were compared with theoretical predictions, and it was found that the values derived from the theoretical equations aligned well with the experimental results. In the second part of the study, a regression analysis was conducted to predict the lateral stresses within the soil. It was concluded that lateral stresses can be estimated with a high degree of accuracy using the proposed regression model (R² = 0.982).

In this study, the usability of construction and demolition waste (CDW) aggregates as filling when stabilized with alkaline activator solution (AAS) and blast furnace slag (BFS) was investigated. The initial stage of this study involved determining the engineering properties of CDW by laboratory experiments. In the next stage, modified Proctor tests were performed to investigate the compaction behavior of CDW, to which 5% to 30% BFS was added with water or AAS. In the following stage, California bearing ratio experiments were performed to determine the mixture specimen with the highest strength. In the final stage, a weak soil layer was created in a test tank, and fillings of different thicknesses were built on it using CDW with and without additives in the determined optimum mixing ratio. Then, plate-loading tests were conducted using a model foundation to evaluate the load–deformation behavior of the fillings. The study’s results indicated that adding BFS with water or AAS to CDW increased strength. Furthermore, the addition of 20% BFS yielded the highest strength value, and the CDW aggregates with the added BFS increased the ultimate bearing capacity by up to 4.72 times compared to those without the additive.

Since construction and demolition waste (CDW) contain materials such as gypsum, wood, brick, plaster, etc., its engineering properties may not be at the desired quality. Therefore, if CDW is to be recycled and reused, the properties of CDW may need to be improved by various methods. In this study, the modifications in compaction and strength properties of CDW obtained from demolished building were investigated by adding fly ash (FA) at certain ratios. For this purpose, modified proctor, unconfined compression strength and California bearing ratio (CBR) tests were conducted on the CDW with and without FA-added. As a result of the experimental studies, it was observed that the addition of alkaline activator solution (AA) to the CDW increased the strength of the CDW. In addition, the strength of CDW increased significantly with the usage of AA in FA-added CDW samples. The FA additive ratio that gave the highest strength in the tests with water and AA was found to be 5% and 15%, respectively. As a result of the study, it is predicted that CDW with FA and AA can be used as a filling material as an alternative to natural aggregate.

Zeminin kayma mukavemeti, inşa edilecek bir yapının temelinin tasarımında önemli bir rol oynar. İnşaat mühendisleri mevcut zeminlerin, yapı yükünü taşıyabilecek durumda olmasını beklerler. Ancak zaman zaman yapı yükünü taşıyamayan zayıf zeminler ile karşılaşılmaktadır. Bu nedenle bu tür zeminlerin mühendislik özelliklerinin iyileştirilmesi gerekmektedir. Bu çalışma kapsamında, düşük plastisiteli bir kil olan kaolin kilinin mukavemeti, Polipropilen Elyaf (PPF) lifleri ve Polietilen Tereftalat (PET) talaşları kullanılarak laboratuvar ortamında arttırılmaya çalışılmıştır. PPF lifleri düşük maliyeti ve dayanıklılığından dolayı, PET talaşları ise hem ekonomik olması hem de gün geçtikçe artan katı atık hacminin azaltılması amacıyla tercih edilmiştir. Bu amaçla kaolin kiline ağırlıkça %0, %0.5, %1.0, %1.5 ve %2.0 oranlarında PPF lifleri ve PET talaşları ilave edilerek karışımlar oluşturulmuş ve Proctor deneyleri yardımıyla optimum su muhtevaları (wopt) ve maksimum kuru birim hacim ağırlıkları (γkmaks) belirlenmiştir. Proctor sıkılığında hazırlanmış numuneler üzerinde serbest basınç deneyleri yapılmıştır. Yapılan deneyler sonucunda katkılı kaolin kilinin mukavemetinde dikkate değer artışlar olduğu tespit edilmiştir. Optimum su muhtevasında ve Proctor sıkılığında hazırlanan numuneler üzerinde yapılan deney sonuçlarına göre %2.0 PPF eklenen kaolin kilinin serbest basınç mukavemeti, katkısız kaolin kili numunelere göre %116 oranında artış göstermiştir. Aynı oranda PET katkısı ile iyileştirilen kaolin kilinde ise serbest basınç mukavemeti %36 artış göstermiştir.

Yeni binaların inşası ve mevcut yapıların yıkılması sırasında büyük miktarlarda atık ortaya çıkmaktadır. Atıkların açık havada depolanması veya bertaraf edilmesi önemli çevre ve sağlık riskleri oluşturmaktadır. İnşaat projelerinde Geri Dönüştürülmüş Beton Agregasının (GDA) kullanılması, hem finansal hem de çevresel açıdan sürdürülebilir büyüme için çok önemli bir stratejidir. Bu çalışmada, inşaat ve yıkım atıklarıyla güçlendirilmiş kum zeminin mukavemet özellikleri incelenmiştir. Deneylerde, sahadaki sıkıştırılmış dolguları modellemek için %80 rölatif sıkılık sahip bir zemin kullanılmıştır. Bu kum zemin önce katkısız olarak hazırlanmış ve içsel sürtünme açısını belirlemek için kesme kutusu deneyi yapılmıştır. Kum zemin daha sonra ağırlıkça %5, %10, %15 ve %20 oranında 2 mm ile 4.76 mm arasında elenmiş GDA ile karıştırılmış ve her bir GDA oranı için mukavemet parametreleri belirlenmiştir. Aynı deneyler, boyutları 4.76 mm ile 6.30 mm arasında olan GDA kullanılarak tekrarlanmıştır. Yapılan deneyler sonucunda, GDA oranı arttıkça zeminin birim hacim ağırlığının %4’e varan oranlarda artış gösterdiği ve içsel sürtünme açısının ise %14’e varan oranlarda artış gösterdiği belirlenmiştir. Artan GDA boyutu ile içsel sürtünme açısının da artış gösterdiği görülmüştür.

Estimating a pile shaft’s frictional capacity is challenging and has been a controversial subject among researchers. In this study, the shaft friction resistance of non-displacement (pre-installed) model piles under axial load was investigated. Four different model piles were used, including steel, timber, and two composite piles (FRP and PVC filled with concrete). The angle of interface friction (δ) between test sand, and pile materials was determined using an interface shear test (IST) at four relative densities. Axial pile load experiments were implemented in a soil tank and piles were embedded into loose to very dense sand. Model pile load tests were performed in such a way that there was no end (point) bearing capacity (only friction was generated), and lateral friction resistance between the pile material and the soil along the pile shaft formed the complete bearing capacity of the model pile. According to experimental results, it was observed that, with increasing sand relative density and surface roughness of the pile material, the shaft friction resistance of the model pile increases. A back-calculation analysis was also performed to find the values of lateral earth pressure coefficient (K) using Burland’s (1973) equation with the help of measured shaft friction capacity of the model pile load test. By performing multivariate regression analysis, an equation was obtained between the back-calculated lateral earth pressure coefficient (K) and other parameters. The obtained equation was used to calculate the K values given in other studies in the literature. It was determined that the obtained equation was in good agreement with the data in other studies. This equation can be beneficial in practice and can be advantageous for further study in the future.

In this study, the load distribution of the piles in the pile group was investigated in the case of the pile raft foundations failure under the effect of vertical loads in cohesive soils. For this purpose, loading tests were carried out on model pile groups in the laboratory. In addition, the effects of these conditions on the load distribution between the piles were examined by changing the pile spacing and soil properties. As a result of the experiments, it was determined that the piles in the corner region carried more load than the ones in the center region in small settlement amounts as in the literature. However, it has been determined that as the amount of settlement in the pile foundation increases, the soil between piles behaves like a block and approaches failure, and the piles in the center region of the pile group carry more load. As a result of excessive settlement, a fracture surface formed around the block and therefore the corner piles of the block began to carry less load. It has been determined that failure analyses should be performed considering the load carried by the corner piles after failure due to excessive settlement.

Historical masonry structures are very important as they carry cultural heritage, so it is important to protect these structures from natural disasters such as earthquakes and transferred to the next generations. It is known that masonry structures are weak against earthquakes, therefore, a suitable analysis method for assessment and retrofitting purposes is a must. Generally, the fixed-base concept is used for analysis and design purposes, however, in reality, the structures are not fixed-base but they are resting on soils. The aim of this study is to make a comparison study between dynamic responses of fixed-base and soil-structure interaction (SSI) models for bridge masonry structures, the historical Dalal bridge was selected as the case study. First, the bridge was modeled as a fixed base model, and then three different soil profiles (hard, medium and soft soils) were added to the underneath of the structure. The numerical models were analyzed under Elcentro earthquake record. Results indicating a good agreement between the fixed base and the case of hard soil base. However, considerable differences were observed for medium and soft soil profiles.