ABSTRACT:

This paper examines the application of triangulation-based laser imaging for rock mass classification. Most case studies in this area have focused on the application of LIDAR and photogrammetry surveys. Triangulation-based 3D laser cameras are a worthy alternative although little research has been conducted. These cameras are designed for short-distances, usually less than 10 m, and are typically immune to the ambient lighting conditions. Three spatial coordinates (X, Y, Z) and the reflection intensity (I) are acquired by triangulating the projected and reflected laser beam paths. A typical image can take between 1-10 minutes to acquire and contain up to 1 million image elements at sub-millimeter accuracies. The short range, immunity to lighting conditions, and high accuracy of these cameras are ideal for an underground environment where there is limited space and lighting, and where the rock face features can be very subtle. A case study was conducted in an underground mine where good correlation was found between joint set orientation measurements acquired manually and with a triangulationbased laser camera. This correlation validates the triangulation-based laser imaging technology and the methodology used for image processing and analysis. Overall, there is good potential in the application of triangulation-based laser imaging to aid in rock mass classification.

1. INTRODUCTION

Rock mass characterization is an essential component in the design of safe underground excavations. Several classification methods exist but the Rock Mass Rating (RMR) system is the most widely used. This classification system considers several parameters in the rock mass including the orientation, spacing, and surface characteristics of joint sets. To estimate these parameters, manual inclinometer measurements are required at the rock face which can be difficult to obtain. There can be safety issues if the rock mass is unstable. Accessibility constraints are also common where only specific regions of the rock mass can be mapped. There can also be time constraints and cost concerns which limit the amount of data collected. Photogrammetric technologies and laser imaging have recently been recognized as valuable tools for structural mapping and rock mass characterization through case studies and workshops [1]. Compared to manual methods, a large amount of data can be acquired safely, including areas that would typically be inaccessible. The data can be processed quickly, and it also serves as a permanent digital record of the rock mass allowing for additional examination at later dates.

1.1. Photogrammetry

Photogrammetry is extensively used in remote sensing for mapping and surveying applications. With this technology, three-dimensional (3D) information is extracted from multiple two-dimensional (2D) images taken from various points of view. The exact location where each image is acquired must be recorded. In these systems, the 2D images are captured using digital cameras. There are several benefits to photogrammetry which lends itself to mapping rock structure. The methodology is simple to understand and is well established. Digital cameras are easy to operate and transport. Successful case studies have been conducted at open pit mines [2, 3]. However, there are limitations to photogrammetry. Digital cameras must typically be calibrated on site each time.

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