ABSTRACT
TBM tunneling is usually performed in a series of cyclic operations which include several activities. In each excavation cycle, individual activities can cause certain delays, which are usually referred to as the TBM being "down", hence downtime (Nelson et al., 1985). TBM performance and daily advance rate depends on the duration of these down times. As the proportion of downtimes increases, the performance of the TBM declines since the net boring time of the machine decreases. For example, in poor ground, the duration of time spent on ground support installation or ground improvement increases which results in low utilization rates, even lower than 10%. Understanding of the causes of downtimes is the key to successful planning of the TBM tunneling and improving machine performance.
