Down time analysis of hard rock TBM case histories

One of the major components of evaluating TBM performance is down time analysis. In most TBM applications, the proportion of downtime is higher than the boring or production time. Study and development of the predictive capabilities for estimation of downtime and subsequently machine utilization in a given project is one of the requirements for accurate estimation of TBM performance and daily advance rate. This paper will offer in-depth analysis of reported downtime for different hard rock TBM tunneling projects including some that are underway or completed in recent years. This includes the analysis of records for various activities for 89 TBM tunnel projects from around the world. This will include the comparison of recorded downtimes with those predicted by the existing models. The poor correlation between predicted and actual downtime components can be attributed to several factors such as lack of a uniform protocol for recording and classifying the downtimes and/or averaging effects of downtimes over the whole length of the tunnel or certain subset. Also, the study indicates that the previous published empirical models might be outdated or in some cases incompatible with new machines and their operational settings. This study will identify and analyze the different causes of downtime on the basis of average duration of each individual activity and will offer some guidelines for prediction of downtime for given project conditions.