Experiences of utility microtunnelling in Irish limestone, mudstone and sandstone rock

There is currently no published guidance on the excavatability of Irish rock for microtunnelling applications. In this paper, new data and experiences of microtunnelling through rock (using a Herrenknecht AVN slurry shield machine with a rock head) at five Irish sites are presented and interpreted. The rock type is limestone at three of the sites, with mudstone/conglomerate and sandstone at the other two sites. The jacking forces are separated into face and friction (between the concrete pipe and rock) components. Useful relationships have been established between the excavatability index and the uniaxial compressive strength and brittleness index of rock. Cutter head wear is discussed in the context of rotational distance travelled and rock strength. In addition, the suitability of a number of prediction models documented in the literature for the prediction of microtunnel boring machine performance in Irish rock is examined. (C) 2015 Elsevier Ltd. All rights reserved.