Abstract

This study proposes a processing procedure to extract the 3D rock structure directly from point clouds using open source software. The basic processing involves: (1) estimating the Hough’s normal of each point; (2) converting the normal to dip direction and dip of the corresponding plane; (3) coloring each point in HSV color space according to its normal; (4) decoding the sets number using the multivariate kernel density estimators; (5) extracting and visualizing the set-based points; and (6) estimating the set-based geometric parameters and conducting stereographic projection. The result is an actual discrete fracture network aggregated with the set-based point clouds having HSV colors. From the initial point cloud to the completion of processing, we manage all data in one single file. The case studies show that the processing procedure can identify, extract, and quantify the fracture sets that have less exposed areas, which facilitates the evaluation of main risks.

Introduction

The establishment of overall geometrical configuration of geological fractures in hard rocks is the fundament of a prudent engineering design. The degree of detail required for characterization varies considerably from applications and project stage. For an assessment of the overall rock mass quality, for example, the techniques of scanline and scan window on two-dimensional rock exposures can sample the data such as orientation, spacing and trace length. The estimated fracture parameters, together with intact rock properties, groundwater and stress condition, are the basis for rock mass classifications. In order to evaluate the main risks, it is necessary to consider the three-dimensional spatial organization of fracture sets. For example, in order to maintain the desired excavation geometry during a drill and blast tunneling it is desirable to identify the boundary fractures of removable blocks. The assessment of rockfall hazard in the Alps is an example where the actual fracture pattern of the rockfall source area is indispensable. However, the attempts to investigate the location-dependent rock structure are often confronted with difficult and dangerous accessibility to the rock outcrops, e.g. in an operational environment of tunneling or on rock cliffs situated a few hundred meters above valley floor.

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