Slope stability designs are largely dependent on rock mass and more specifically discontinuity characterization. Traditional discontinuity characterization methods (scanline and cell mapping) have many problems associated with time, safety, accuracy, and human bias. This study shows how 3D imaging using ground based LiDAR scans and digital photography can be used to collect discontinuity information for slope stability analysis. 3D imaging allows for potentially larger data sets to be collected rapidly while eliminating or highly limiting the problems with traditional methods. Rock mass information for a benched road cut was gathered using traditional and 3D imaging methods. A set of NIOSH slope stability programs were then compared to two other commercial programs using the two different data sets gathered. 3D imaging was used to create an "as built" of a benched road cut. This image was used to test the accuracy of the three slope programs. The comparison between programs resulted in similar conclusions despite which data set was used. All slope modeling programs results contained slight inaccuracy when compared to the actual slope.
Predicting the stability of a rock slope is vital to the construction and mining industries. Slope instability is a leading cause of fatalities in surface mining . Correctly designing stable slopes increase safety and production as well as reducing construction time and cost. Slope stability designs are largely dependent on the characteristics of the rock mass and more specifically discontinuity characterization. Discontinuities in this study refer to: joints, fractures, bedding planes, or any other visible planes of weakness within the rock mass.
Traditional methods for characterizing discontinuities include scanline surveys and cell mapping [2,3]. Scanline (detailed line) surveys are conducted by laying a tape measure along a rock face and discontinuity characteristics are measured for every discontinuity crossed. Cell (area) mapping is conducted by breaking the rock mass into multiple areas of equal size. Discontinuity characteristics are measured for each set within these different areas (cells). Although these methods have proven to be very effective there are many drawbacks associated with them, including time, accessibility, and human bias . Recent advances in imaging technologies show the potential to eliminate or highly reduce these problems. These advantages will be discussed later in this paper.
1.1. Imaging Technologies
The two predominate imaging technologies, 3D LiDAR scanning and digital photography, show the most potential for rock mass characterization purposes. Below is a brief discussion of how each technology works. For more detailed analysis on how the different technologies work or other possible imaging technologies please see Baltsavias [5,6,7].
LiDAR (Light Detection And Ranging or Light RADar) uses a time of flight light pulses to generate a 3D image of a surface. A light pulse is emitted from the source, reflects off the surface of an object and returns to the source. A high precision counter measures the travel time and intensity of the returned pulse. Thus the distance from the source to a point on some surface as well as the reflectivity of that surface can be measured with great accuracy.