Mechanical behavior of multi-scale fiber-reinforced concrete for secondary tunnel lining: Field test and numerical simulation

The application of polypropylene fiber in the secondary tunnel lining can provide theoretical guidance for preventing and controlling tunnel lining problems from the perspective of concrete materials. The field tests and long-term observations were carried out to study the inhibitory effect of multi-scale polypropylene fiber-reinforced concrete (MPFRC) on tunnel lining problems and the mechanical characteristics of MPFRC for secondary tunnel lining. The tunnel appearance, concrete lining strength, the contact pressure between the primary and secondary linings and concrete strain were investigated. Besides, the influences of thickness and reinforcement ratio on the stress of MPFRC for secondary tunnel lining under external load were analyzed based on numerical simulation. The results show that: (1) The re-casting of the secondary lining will cause the stress redistribution of the surrounding rock of the primary support. (2) Compared with ordinary concrete, the time-strain curve of MPFRC is flatter and the variation range of the strain value is smaller, with a reduced rate of 45.45 %. (3) MPFRC can reduce the secondary tunnel lining's thickness and hoop reinforcement rate by about 22 % and 25 %, respectively. The research results can provide a reference for the prevention and treatment of lining cracking, water leakage, corrosion and other problems, and provide a theoretical basis for the optimal design of secondary tunnel lining.