A new spectral analysis method for determining the joint roughness coefficient of rock joints

We propose a new spectral analysis method for accurate JRC determination. To do this, we first propose an average power index Pf to present the amplitude height of a rock joint profile, which considers both the low and high-frequency components of the profile. Secondly, the modified root mean square of the first deviation of the profile (Z(2)*) is adopted to better capture the effects of shear direction and the inclination angle of the profile on the rock joint's roughness. Finally, we propose a new roughness parameter, PZ, which combines the Pf and the Z(2)*; the PZ considers the shear direction, the inclination angle and the amplitude height of a rock joint profile simultaneously. We derived correlations with upper, suggested, and lower bounds between JRC and PZ using 102 rock joint profiles at the sampling interval of 0.4 mm, and compared them with Barton's 10 standard rock joint profiles. We analyzed five sandstone joints from the field to validate the proposed method: Both laser scanning and direct shear tests were conducted on the sandstone joints. Comparing the peak shear strength obtained from experimental tests, the proposed method, and the Z(2) method, verified that the proposed method can determine the JRC accurately. In addition, the shear direction influence and sampling interval effect on the rock joint roughness were discussed. The correlations between JRC and PZ were also derived at the sampling intervals of 0.8 mm and 1.2 mm.