Probabilistic estimation of the advancement rate of the Tunnel Boring Machines on the basis of rock mass characteristics

Abstract: The prediction of the advancement rate of a Tunnel Boring Machine (TBM) is one of the most important aspects of the design phase of a rock tunnel. Many authors have deepened the argument, coming to estimate this value as a function of some characteristics of the rock and of the excavation machine. Among the many developed systems, one of the most complete and effective is the one proposed by Norwegian University of Science and Technology (NTNU). Unfortunately, the complexity of the phenomenon studied requires evaluating many characteristic parameters of the rock mass in some cases not known or known only with poor precision. In this work a new probabilistic procedure is developed, based on the study of the NTNU, able to estimate the variability interval of the advancement of the TBM per revolution of the TBM head i, with the associated reliability, referring to the most common characteristic parameters of the rock mass: number of discontinuity sets, type of discontinuities, average spacing between discontinuities, uniaxial compressive strength of the intact rock (UCS). Some abacuses have been pre-arranged in order to facilitate the evaluation for all the practical cases that can be encountered in the excavation of rock tunnels. An application to the well-known case of the Tunnel of Varzo (North-West of Italy) made it possible to compare the results of the probabilistic study with the net rate actually measured on the TBM. Article highlights: The NTNU system is one of the most important prediction model for advancement rate for TBM.A new probabilistic procedure is developed, based on the NTNU model.The variability interval of i is estimated considering some characteristic parameters of the rock mass.