Use of Synthetic, Fiber-Reinforced, Initial Shotcrete Lining at Devil's Slide Tunnel Project in California

Fiber-reinforced shotcrete is widely used as a temporary excavation support in the construction of transportation tunnels and in other civil applications that are performed with the Sequential Excavation Method. Traditionally, steel fibers have been used in tunnel construction; however, the use of synthetic fibers is becoming more common. At the Devil's Slide Tunnel Project, on Highway CA-1 in Pacifica, California, a synthetic fiber mix was used to achieve the contract initial lining performance. The synthetic (polypropylene) fiber was used throughout the excavation phase of the twin highway tunnels and was tested with the round determinate panel test (ASTM C1550) for its capability to absorb energy after shotcrete section failure (flexural strength). The contract required the ASTM C1550 test to produce at least 320 J at 40 mm of deflection after 7 days. This paper discusses the testing program and summarizes its results. The overall performance of the fiber-reinforced shotcrete liner is discussed and evaluated on the basis of its reaction to deformation and its use in the tunnel.