Engineering characteristics of high-weight aged BOFs-dredged soil backfill for port structure: Shear properties, unit weight, strength, and microstructure characteristics

The seismic stability of port structures is highly influenced by the submerged unit weight of the backfill material. Conventional light weight treated soils (LTS) often fall short in meeting the stability requirements under seismic conditions due to their limited weight. To address this limitation, the present study proposes a high weight backfill material incorporating industrial by-products specifically, basic oxygen furnace slag (BOFs) and marine dredged clay (MDC) soils. The study utilized aged, aggregate type BOFs and a small amount of cement as the primary binder, along with marine dredged clay soil as the main matrix, to evaluate the frictional properties, unit weight, microstructure, and unconfined compressive strength (UCS) behavior. These evaluations were conducted using surface roughness measurements, direct shear tests, and UCS tests, considering key mix design variables such as BOFs particle size and content, cement addition and dosage, water content, and curing times. The results of this study indicate that an increase in BOFs particle size significantly enhances interfacial roughness and shear strength parameters, such as cohesion and internal friction angle. Additionally, the unit weight of the mixture tends to increase with both the particle size and content of BOFs. The unconfined compressive strength (UCS) was notably improved under conditions of low water content and high BOFs content. Although the effects of particle size and content varied, the inclusion of a small amount of cement (5 %) led to a marked improvement in strength development. These findings are well supported by the microstructural observations obtained through SEM analysis. In addition, a predictive model for the UCS of BOFs-MDC weight soil was developed based on the BOFs volume fraction, curing time, and a particle size coefficient. The findings of this study elucidate the fundamental mechanical behavior of BOFs-MDC weight soil mixtures and offer a foundation for optimal mix design and practical field applications in seismic-prone port environments.