Experimental study on the vacuum consolidation of recycled fibre-improved soft soils assisted with prefabricated vertical drain

Billions of face masks were discarded daily, causing severe environmental concerns. Recycling waste face masks presents a significant challenge. Meanwhile, the traditional vacuum preloading shows limitations on the performance on soft soil ground. This paper investigates the potential benefits of reusing Face-Mask Fibres (FMF) as an admixture to enhance the treatment effects of vacuum preloading on soft soils. The performance of an environmentally biodegradable type of Prefabricated Vertical Drain (PVD) is also compared with that of conventional PVD through a series of laboratory physical model tests. The settlement, distributions of vacuum pressure, porewater pressure, and water content were monitored. In addition, after vacuum preloading, the undrained shear strength of treated soil was determined. Scanning electron microscope tests were also carried out to analyse the microscopic structure of treated soil. Results reveal that face-mask fibres significantly improved the performances of vacuum preloading in terms of vacuum dewatering and strengthening. Furthermore, the rate of vacuum consolidation was accelerated due to the additional drainage channels provided by recycled face-mask fibres. Notably, the final water content of the treated soil decreased to 41.8%, which is markedly lower than the liquid limit of 63.9%. The undrained shear strength exhibited considerable improvement, nearly doubling in value. The mechanism of how FMF works was also discussed.