ABSTRACT
Raise boring is a well-established form of mechanical hard rock excavation that is used for the construction of increasingly long and large diameter shafts for purposes such as tunnel and mine ventilation. The procedure requires access to the bottom end of the new shaft and consists of two steps: first, a small diameter pilot hole is drilled top-down. Secondly, a reamer head equipped with raise cutters is connected to the drill string and pulled up while rotating, thus enlarging the pilot hole to a circular shaft. This step is referred to as reaming, and it is the focus of this research. In challenging geological conditions, the reamer structure faces highly dynamic conditions with high-amplitude vibration and shock loads, which can result in damage to the cutters, blockages, instant failure or fatigue failure of the reamer components. To gain an improved understanding of these dynamic phenomena, a measurement setup consisting of acceleration and turning rate sensors in three axes was installed on a reamer. Shock and vibration data was successfully captured during the raising of several hundred meters of shafts. These experimental dynamic measurements are used to identify and analyze potentially damaging irregularities during operations, as well as to better understand the reaming process in general. The data collected insitu is also employed in conjunction with finite element modelling to analyze the dynamic forces acting on the reamer and its components during the reaming process by calculating power spectral densities. The end goal is to predict potential fatigue damage, thus facilitating design improvements and predictive maintenance in order to optimize reaming operations and reduce equipment down-time.
