This paper proposes a reasonable synthetic fiber-reinforced shotcrete application method by analyzing the behavior of synthetic fiber reinforced shotcrete by tunnel rock support class.
The continuum numerical analysis was performed considering the size, shape, rock condition, and coefficient of lateral pressure(Ko) of typical domestic traffic tunnels(highway tunnels and railway double and single track tunnels). Face Mapping data of the tunnel site were analyzed to examine the characteristics of the joint surface distribution according to the rock support class. Also, compressive strength, flexural strength and flexural toughness test of steel fiber and structural synthetic fiber(PP fiber) reinforced shotcrete were carried out for the application of fiber-reinforced shotcrete.
Numerical analysis results and Face Mapping analysis results by the tunnel rock support class were reviewed extensively.
As a result, it is considered that the application of general shotcrete to the full section is appropriate because the rock support class I, II, III-1(RMR=60～51) have a small tunneling displacement and a shotcrete stress and good joint characteristics. Also it is considered that the application of the fiber-reinforced shotcrete is appropriate because the tunnelling displacement and shotcrete stress are large and many joints are distributed in the rock support classⅢ-2(RMR=50～41), Ⅳ and Ⅴ. However, in the case of rock support class IV, since the change of tunnel deformation and shotcrete stress due to the tunnel underground excavation is very small, a general shotcrete application was proposed.
The flexural toughness, which is the most important characteristic of shotcrete as a tunnel support material, is considered to be equal to or larger than that of the steel fiber reinforced shotcrete. The energy absorbing capacity(J) of the steel fiber reinforced shotcrete was evaluated to be low due to the rapid residual strength reduction. However, the energy absorbing capacity of PP fiber reinforced shotcrete was measured to be relatively high. As a result, it is considered that the PP fiber reinforced shotcrete has a higher supporting ability than the steel fiber reinforced shotcrete.
The flexural toughness-energy absorbing capacity interaction equation is proposed by analyzing the results of the beam and circular panel shotcrete flexural toughness test, so that the flexural toughness of the shotcrete can be evaluated as the flexural toughness grade of the energy absorbing capacity concept. Q value-PP fiber mixing amount interaction equation is proposed to design the mixing amount of PP fiber according to rock support class.
The study on the application of shotcrete support by rock support class and the study on the application of reinforcing shotcrete of fiber (steel fiber and PP fiber) are synthetically reviewed propose a tunnel shotcrete optimization design scheme as shown in Table V-1.
When the results of this study are applied to the design of tunnel supports, the stability and the construction and economic efficiencies of tunnels are expected to be greatly improved.