ABSTRACT

Virtual outcrop models (VOMs) are three-dimensional computer based representations of engineering rock mass characteristics, especially fracture geometries. This paper describes a rock mass modeling procedure for capturing, processing and extracting relevant engineering geologic data and measurements from outcrops, based on the synergistic combination of terrestrial laser scanning (TLS), digital photogrammetry, and precise RTK-GPS surveying. The resulting VOM is geo-referenced and conveys multi-scaled spatial data over the entire project domain, greatly facilitating general outcrop studies and the detailed measurement of rock mass structures. A general VOM of Salza Dam in the upper Styria region of Austria demonstrates our multiscaled VOM approach for the assessment of rock scour, and applications to detailed structural measurements are made with TLS data from the Angenofen rock quarry near Graz, Austria. Results from these field studies show that meshed and textured digital terrain models facilitate unbiased and confident measurements of rock mass structures with unprecedented accuracy and resolution.

1. INTRODUCTION

The digital characterization of fractured rock masses is an important topic in rock engineering practice. With the introduction of remote sensing technologies, especially terrestrial laser scanning (TLS), rock mass structures can be characterized with unprecedented accuracy and resolution [e.g. 1, 2, 3, 4, 5]. The TLS technology is thus a valuable compliment to traditional field studies. However, due to differences in LiDAR (Light Detection and Ranging) hardware and post-processing capabilities, procedures for constructing digital outcrop models are non-standardized. Extracting fracture orientation information from laser point clouds is a typical example, wherein some researchers favor automatic detecting, and others prefer manual fitting. In this paper we introduce a novel Virtual Outcrop Model (VOM) approach for the three-dimensional characterization of engineering rock masses. A virtual outcrop model is a computer-based three-dimensional representation of engineering rock mass properties, especially data on fracture geometries. Main objectives of our VOM include:

? Accurately geo-referenced and multi-scaled spatial data over the entire range of a project. This is a decisive difference to traditional engineering geological maps which are generally the twodimensional representations at a single scale [6, 7]. In our VOM, the information density of the important and critical areas is unprecedented.

? Construction of high-resolution, photo-realistic, true color 3D images to facilitate digital interpretations and measurements of fractured rock masses, especially their structural geological patterns.

? Development of digital 3D geo-referenced multiscale base maps for direct compilation of field information (for example using tablet computers).

? Digital measurement of fracture orientation, spacing, persistence, surface roughness as well rock block and rock bridge patterns.

? Detailed measurement of terrain geometry, such as slope angle and height, over- and underbreak of underground excavations, as well as slope instability and surface erosion features. Enumerated below are details of the LiDAR hardware and software employed in our studies, together with workflow procedure for acquiring data and constructing a VOM. Finally, example applications in rock engineering are summarized.

2. LIDAR SURVEY HARDWARE

In the current VOM study, a Riegl 3D terrestrial static 3D laser scanner was used to acquire 3D point data sets from surface outcrops.

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