Fracture Mechanics Design For Primary Support Of Tunnel With Sprayed Steel Fiber Reinforced Concrete

Steel fiber reinforced concrete is a new type of composite material with advantage of high ductility and high impact resistance. The construction costs of the application of the steel fiber reinforced concrete in tunnel support system is lower than that of normal concrete due to decrease the thickness of the lining and replace the mesh reinforcement and the maintenance cost is lower with its high seepage resistance and fracture resistance.From the field mechanics and ductility tests of the specimens in the WuLong tunnel, it indicated that the steel fiber reinforced concrete shotcrete has higher ductility and more fracture resistance than these of normal concrete. The reasonable materials ratio of the steel fiber reinforced concrete shotcrete was suggested. The strength and ductility characters of the steel fiber reinforced concrete shotcrete were researched from the view of fracture mechanics. And according to the experiemental data and the results from post-experimental analysis, a modification on the thickness design procedure of the tunnel lining is proposed in this paper based on the fracture mechanics procedure adopted in the Code of Japan. For the load-baring capacity of the initial lining using steel fiber reinforced concrete, a modified fracture mechanics method is used in this paper to achieve the design purpose. It indicated that the steel fiber reinforced concrete shotcrete still has the strength capacity and does not have brittle behavior after fracture due to high ductility. So, the steel fiber reinforced concrete shotcrete is more suitable in large displacement conditions. Back-Calculation was conducted for the V rock supported by the steel fiber reinforced concrete shotcrete from the field measurement. It indicated that the V rock is stable supported by the steel fiber reinforced concrete shotcrete. It suggests that it is applicable to use the steel fiber reinforced concrete shotcrete to support tunnel primarily and it is conservative to design the steel fiber reinforced concrete shotcrete by fracturemechanics.