- Copyright © 2015, Environmental & Engineering Geoscience
Vertical or sub-vertical discontinuities striking parallel to rock cuts are dangerous because toppling and spontaneous raveling failures can initiate from these surfaces, creating hazards below. At the same time these surfaces are often hidden, because they do not daylight into the cut on either side, and any trace of the discontinuity that might be seen at the top of the cut is obscured by overburden. These hidden discontinuities can often be detected by Ground Penetrating Radar (GPR). Used in conjunction with Terrestrial LIDAR (LIght Detection And Ranging), it is possible to accurately measure the orientation of these hidden discontinuities. The method presented in this paper establishes three control points on the surface of the rock cut. At each control point the global coordinates are measured using LIDAR. GPR soundings at each control point are used to measure the perpendicular horizontal distance (depth) to any discontinuities hidden behind the rock face by GPR. The true perpendicular distance is added to the GPR coordinates at each control point to form three new control points on the surface of each of the hidden discontinuities. Using the three point method the orientation of the hidden discontinuity is calculated.