3D laser imaging for joint orientation analysis

This paper evaluates the application of three-dimensional (3D) laser imaging to measure joint orientation. A field trial was conducted at a road cut with 3 well expressed joint sets. Using 3D point cloud data, joint orientation was evaluated using two methods: a 2.5D method, commercially available, based on a triangular irregular network (TIN) and a new 3D pole density contouring method where the orientation of each triangular mesh element in the 3D model is determined. Validated against field measurements, the 2.5D and 3D methods were applied manually and the resultant average angular differences were 13.3° and 3.8°, respectively, indicating that the 3D method is very accurate. When automated, the 2.5D and 3D methods yielded results with average angular differences of 14.4° and 9.9°. The effects of image resolution (an image acquisition parameter), triangular mesh element size (an image processing parameter), and joint face geometry (a geological parameter) on the performance of the 3D pole density contouring method were assessed. Image resolution had minimal effect on measurement accuracy. Increasing triangular mesh element size had an adverse effect because holes started to appear in the 3D model.

► Laser imaging captures rock face topology and converts it into a 3D model.
► A new method computes the orientation of each model element and outputs stereonets.
► Image resolution has minimal impact on accuracy of joint orientation measurement.
► Optimal 3D model element size is estimated from a ratio of the model vertices.
► Optimal 3D model element size is estimated from the geometry of the joint face.