Greif V. & Drotár T., 2011: Estimation of joint roughness coefficient JRC by close-range digital photogrammetry. Acta Geologica Slovaca, 3, 2, 163–172. (in Slovak with English summary)

Stanovenie koeficientu drsnosti puklín JRC metódou blízkej digitálnej fotogrametrie

Estimation of joint roughness coefficient JRC by close-range digital photogrammetry

Vladimír Greif & Tomáš Drotár

Katedra inžinierskej geológie, Prírodovedecká fakulta, Univerzita Komenského v Bratislave, Mlynská dolina G, 842 15 Bratislava; greif@fns.uniba.sk, tomas.drotar@gmail.com

Abstract

This work deals with the evaluation of joint roughness coefficient (JRC) in the rock mass based on the digital photogrammetry and its comparison with traditional method of JRC estimation using linear profiling. The JRC value is used for the estimation of shear strength of discontinuities in rock mass. First method used for JRC determination was the method using comb profilometer used to create roughness profiles by tracing the cross-sections to the paper and digitizing them. The second method made use of principles of digital photogrammetry, where digital images were used for the creation of 3D model of joint surface, from which roughness profiles were extracted. Both methods were used at the Devínska cesta road cut in Bratislava. The profiles obtained by two methods were compared visually with the standard profiles. Based on this comparison each profile was given a JRC value which is necessary input for the estimation of joint shear strength. The value of JRC obtained by both methods was in range 14–16 corresponding to the standard profile no. 8. Further, both methods, contact and non-contact, were compared by subtracting both curves and statistically analyzing the difference in more than 1500 sampling points. The results showed that the standard deviation in the case of profile 16–17 was 0.422 mm, which represents 4.4 % of the roughness amplitude, while for the profile 22–23 the standard deviation was 0.35 mm, representing 3.5 % of the roughness amplitude. Both standard deviations were under the 5 % margin, which gives good indication of the acceptability of photogrammetric method of JRC determination.

Key words: digital photogrammetry, joint roughness coefficient, comb profilometer, Bratislava-Devínska cesta road cut

Manuscript received: 2011-09-12

Revised version accepted: 2011-10-19