Practical shotcrete rock reinforcement for hard rock openings

Abstract

Conventional cast in-situ concrete linings are a costly, time consuming activity and environmentally unfriendly solution for supporting hard rock excavations because concrete linings are unable to utilise the inherent strength of the rock. In evidence, by the application of confining pressure via pattern bolts suffices to improve the strength of the rockmass at the underground opening (i.e. cavern or tunnel). In the implementation of this measure, the rock arch formed by the tunnel roof and walls is considered to be a supporting arch capable of sustaining a thrust at the arch ends. However, a potential rock wedge failure, of comparatively small size, is highly probable and may occur between rock bolts. To deal with this issue, shotcrete linings will then be introduced to act as thin “protective skin” liners to support the rock surface with performance similar to a reinforced concrete slab. A detailed discussion of these combination measures, so called “shotcrete rock reinforcement” (SRR), including analysis of the strengthened rock arch and the design of shotcrete linings’ structural capacity according to Eurocodes for hard rock underground openings are presented in the paper together with numerical modelling to check against the boundary deformation of openings. Key issues of the constructability of SRR are also discussed.