Fig. 5

Contact surface in sandstone and granite. The contact surface area variation (see also Fig. 2c.5) during the test is shown for Rorschach sandstone (a) and Grimsel granite (b) as a function of tool penetration into the rock. Untreated and post-treatment conditions are indicated by violet squares and green circles, respectively. The data are correlated by parabolic functions (dashed curves) of the type \(S_c=k\cdot \delta ^2\), where \(S_c\) is the contact surface, \(\delta\) is the penetration depth, and the constants are empirically found here, and are given as \(k=2.86\) for Rorschach sandstone and \(k=5.75\) for Grimsel granite. The \(\pm 10\%\) ranges are shown by the gray-shaded regions in a and b