Fig. 7

Cutting forces in granite. The cutting forces exerted on the tool during the scratch experiment are shown in a as a scatter plot for Grimsel granite under untreated (violet squares) and after-treatment (green circles) conditions. Symbol sizes indicate the wear flat values measured at the tool tip (see legend). In b, the compressive stresses exerted on the rock during the test are calculated, using the measured forces and the projected surface area, calculated from the tool penetration depth and the wear flat values. In this plot, the scattered data distributions, representing the strength values, are summarized by boxes, where the central mark indicates the median value, the bottom and top edges of the box indicate the 25th and 75th percentiles, respectively, and the error bars represent the standard deviation range