Use of sedimentary rock impact indices in evaluation of tunnel-boring machine performance

This paper outlines the analytical methods being used to develop Rock Impact Indices (RIIs), a suite of parameters which are used to link Tunnel Boring Machine (TOM) performance to in situ geologic conditions in sedimentary rocks. RIIs will be developed to describe the rock mass by reference to intact rock strength, water inflow and jointing parameters. However, only the derivation of the RII associated with jointing is described in this paper. Discrete values of this index are obtained along the tunnel and linked to local TOM performance measures, penetration rate and utilization. Emphasis is placed on establishing a reasonable representation of the jointing along the length of the tunnel using the RII, derived from tunnel mapping. The relationships unking the RII to TOM performance parameters, as identified from the back-analysis of case history data, are used in the prediction of TOM performance in a simulation program.