Umili_Ferrero_Einstein_final.doc - 1 A new method for automatic discontinuity traces sampling on rock mass 3D model 2 Umili G(a Ferrero A(a Einstein

Umili_Ferrero_Einstein_final.doc - 1 A new method for...

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A new method for automatic discontinuity traces sampling on rock mass 3D model Umili G. (a) , Ferrero A. (a) , Einstein H.H. (b) (a) Department of Civil, Environmental and Territory Engineering, University of Parma, Viale G.P. Usberti, 181/A 43124 Parma, Italy. [email protected], [email protected] (b) Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. [email protected] Corresponding author: Anna Maria Ferrero Department of Civil, Environmental and Territory Engineering, University of Parma, Viale G.P. Usberti, 181/A 43124 Parma, Italy. e-mail: [email protected] telephone: +39 0521 906055 fax: +39 0521 905924 ABSTRACT: A new automatic method for discontinuity traces mapping and sampling on a rock mass digital model is described in this work . The implemented procedure allows one to automatically identify discontinuity traces on a Digital Surface Model: traces are detected directly as surface breaklines, by means of maximum and minimum principal curvature values of the vertices that constitute the model surface. Color influence and user errors, that usually characterize the trace mapping on images, are eliminated. Also trace sampling procedures based on circular windows and circular scanlines have been implemented: they are used to infer trace data and to calculate values of mean trace length, expected discontinuity diameter and intensity of rock discontinuities. The method is tested on a case study: 1 1 2 3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 1 2
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results obtained applying the automatic procedure on the DSM of a rock face are compared to those obtained performing a manual sampling on the orthophotograph of the same rock face. Keywords: automatic, trace mapping, rock mass, 3D, curvature, edge. 1. Introduction One of the fundamental parameters to characterize a rock mass is discontinuity persistence, defined as the ratio between the total discontinuity area and a reference area (surface); direct measurements of discontinuity area are quite impossible to obtain, and therefore another discontinuity feature is used to infer discontinuity area and this is the discontinuity trace. Discontinuities are an intrinsic characteristic of rock masses and they appear at every scale of a technical survey. The traditional discontinuity sampling procedure consists of a manual survey performed by an operator directly on the rock mass (ISRM, 1978). However, issues related to the duration of the procedure, to the operator’s safety during the survey and to direct access problems lead many authors to propose non-contact methods, namely, procedures which allow one to perform the trace survey on a representation of the rock mass, such as an image or a digital model. Trace detection on images can be a long and complex operation; in fact, the manual operation is time consuming and an expert operator is needed. Mapping performed by means of edge detection algorithms (Barrow and Tenenbaum, 1981; Canny, 1986; Lindeberg, 2001; Kemeny and Post, 2003) or segmentation techniques (Maerz, 1990; Reid and Harrison, 2000; Post et al., 2001; Lemy and
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