Disc cutting tests in Colorado Red Granite: Implications for TBM performance prediction

A series of full-scale laboratory disc cutting tests was conducted with a single disc cutter (432 mm diameter and a constant cross-section profile) and a single rock type (a coarse-grained red granite). Normal, rolling, and side forces were measured for a series of spacings and penetrations, from which other cutting parameters also were calculated. Although the increases of normal and rolling forces with increased spacing and penetration are as expected, the results illuminate additional aspects of performance prediction. Specific energy (SE) considerations indicate that a spacing of 76 mm is close to optimum in this hard, brittle crystalline rock. At this spacing, penetration has very little effect on SE. These results show why spacings near 76 mm are commonly found on tunnel boring machines operating in hard rock. The relationship of rolling force to normal force was close and consistent: A nearly linear rise of the ratio of rolling force to normal force with increased penetration, and, conversely, a nearly unchanged ratio with increases in spacing. The results tend to validate performance prediction methodologies based on normal force-penetration models.