3-D laser imaging of drill core for fracture detection and Rock Quality Designation

• Lighting and contrast issues typically associated with 2-D imaging removed.
• 3-D imaging eliminates interference from rock texture.
• Semi-automatic computation of the RQD.
• Natural fracture and mechanical break properties quantified.

The Rock Quality Designation (RQD) is a widely used parameter in empirical methods of estimating rock mass strength. This proof of concept research is a step toward the semi-automatic computation of the RQD and is based on 3-D imaging procedures and algorithms to detect fractures in drill core. The images were acquired with a triangulation-based 3-D laser digitizer. Each image file is a point cloud of spatially referenced measurements in Cartesian space. Variations in the z-coordinate (digitizer-to-target distance) were used to detect fractures in profile. Natural fractures were distinguished from mechanical breaks by measuring the angle, and quantifying the roughness, of the fracture trace. The algorithms use a binary centerline profile to measure intact lengths of core for the RQD calculation. This 3-D approach measures changes in the core surface, not intensity features and shadows as with 2-D photographs. Limitations arise when there is no detectable change in the z-coordinate.