Experimental and numerical analysis of tunnel primary support using recycled, and hybrid fiber reinforced shotcrete

Abstract

Shotcrete plays a pivotal role in the construction of tunnels and underground structures; however, its inherent brittleness necessitates reinforcement to enhance ductility. This research explores the use of fiber-reinforced shotcrete as primary tunnel support to enhance ductility and reduce brittleness. Traditional steel mesh reinforcement complexities have led to the investigation of alternative materials. The research evaluates different fiber mix designs, including industrial steel, recycled steel fibers from tires, and Forta fibers, examining their strength parameters and deformation performance. A 3D finite element model is used to simulate a horseshoe-shaped tunnel with optimal mix design and plain shotcrete in a soil environment. The study finds that hybrid industrial and recycled fibers are more effective than single fibers, enhancing compressive, tensile, and flexural strength and reducing ground surface settlement and tensile damage. The optimal mix design of this study has increased compressive, tensile, and flexural strength, as well as flexural toughness, compared to plain shotcrete. Numerical modeling reveals that utilizing fiber reinforced shotcrete made out of optimal fiber mix design as primary support results in a significant reduction in ground surface settlement and tensile damage value. Furthermore, the study shows a significant reduction in the damaged zone area under tensile stresses. The results of the study highlight the potential of fiber reinforced shotcrete as a primary support for tunnels, leading to improved performance and sustainability in tunnel construction.