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Discontinuity mapping with photogrammetry and televiewer for blastability assessment

Publicated to:Isrm International Symposium - Eurock 2020. - 2020-01-01 (), DOI:

Authors: Segarra P; Sanchidrián JA; Bernardini M; Gómez S; Pérez-Fortes AP; Paredes C; Navarro J

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Abstract

Photogrammetry and optical televiewer are used to investigate discontinuities occurring in the highwall of the bench and in eleven blastholes in two blasts. The measuring conditions involve lower resolution for photogrammetry models. Discontinuity mapping was done manually by the same operator. The main rock mass characteristics considered to predict fragmentation from rock blasting (i.e. discontinuities’ orientation and spacing) are obtained from each of these tools. Discontinuities’ spacing has been assessed in photogrammetry models along a dense set of scanlines oriented in four directions along the bench face. The blasthole axis itself is the scanline for televiewer measurements. The orientation of discontinuities is investigated from density contour plots of the poles of the discontinuities measured by both techniques. A sub-horizontal set is observed with both techniques in both blasts, while the number and orientation of sub-vertical sets is different. A procedure to calculate a fracture orientation index for fragmentation prediction models has been applied to the measured discontinuities. The resulting indexes from both techniques in one blast are very similar, while a difference of 14 % occurs in the other blast. Gates-Gaudin-Schuhmann (GGS) and Weibull-Rosin-Rammler (WRR) functions have been fitted to the cumulative distribution functions of discontinuities spacing. Both can represent the spacing data within a limited range, this being narrower for the GGS. The determination coefficients are generally higher for the WRR function, despite the broader range of the fit. Differences in the resolution of the measuring techniques involves a median spacing or scale factor of the WRR function of about 1 m for photogrammetry, and 0.3 m for televiewer. The shape factors of the WRR function from televiewer logs are in line those from scanlines of photogrammetry models. This suggests a scale-invariant behaviour of the discontinuity pattern in the rock mass for the techniques analysed.

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