When designing with rock masses of relatively high intact strength, characterization of the geologic structure properties is a critical component to proper analysis. Data describing distributions of discontinuity orientation, length, spacing and strength for pertinent sets within the rock mass provide the basis of probabilistic models necessary for analysis. Probabilistic methods require a reasonably large sample size in order to provide reasonable estimates of inherent structural variability. The use of laser scanning, or LiDAR, technologies is commonly utilized as a high resolution survey technique but is less frequently used, in conjunction with registered high resolution digital imaging, as a tool for geotechnical data collection. This methodology can provide a cost effective and time efficient means of collecting such large data sets. A case study was carried out to evaluate the correlation between statistical characterization of discontinuity properties acquired manually in the field using oriented core and cell mapping techniques to those obtained remotely using LiDAR. The benefits and limitations of these methods are evaluated and practical recommendations are made based on results of the case study.
When designing with rock masses of relatively high intact strength, characterization of the geologic structure properties is a critical component to proper analysis. Of the highest order of importance is statistical characterization of discontinuity properties such as orientation (dip and dip direction), lengths, spacing and strength for pertinent sets within the rock mass. Each of these parameters is best described by a distribution of values having a central tendency and some variation around that central tendency. A sufficiently large sample of the discontinuity population is necessary for development of a representative model.
Several sampling techniques are commonly used for field geotechnical data collection including oriented core drilling and cell mapping. Analysis of orientated core data can reasonably characterize variability in discontinuity orientation, spacing and small-scale joint conditions but information on discontinuity length and large-scale conditions are unattainable from core due to the relatively small sampling window. Manual data collection techniques, such as cell and detail line mapping can yield useful information for characterization of most discontinuity parameters but are commonly restrained by limited safe access to the rock faces and are also frequently time-excessive.
Remote characterization techniques such as LiDAR (Light Detection and Ranging), or laser scanning, are less commonly used but should be considered valid techniques for rapid and accurate geotechnical data collection. LiDAR can provide thorough characterizations of rock structural properties, including discontinuity orientation, spacing and length and, in some cases, large scale roughness or waviness for both surface and underground rock exposures. Compared to manual methods, a large data set can be obtained relatively quickly and from a safe distance in areas that would otherwise be inaccessible.
The primary advantages of LiDAR over manual field methods include the ability to rapidly obtain direct measurements which are recorded directly into database format during their collection. This potential to have the data directly input into electronic format eliminates the data input, processing and management steps common to most field methods.