The extraction of 3D block structure from a point cloud is a nontrivial but important task in rock engineering. Block in Point Cloud (BLOCKinPCD) is a novel processing system that converts the point cloud data of rock outcrops into 3D rock structure. The workflow and processing functions include: (1) spatially identifying and extracting the point clouds of each discontinuity set; (2) quantifying the geometric parameters of each set (orientation, spacing and persistence); (3) characterizing the in-situ block system by assembling the block-forming sets into discrete fracture network; (4) quantifying the volume distribution of the block system and (5) evaluating the stability of blocks intersecting the excavation surfaces. As shown herein, BLOCKinPCD has been successfully applied to outcrops exposed in rock slopes and tunnel excavations.
One of the challenges in rock engineering relates to the spatial variation of rock structure, which cannot always be characterized in the investigation and design stages. Often, as in the case of tunnel excavation, rock structure details are only revealed during construction. Once the rock is exposed by tunneling, joint traces can be mapped, as a basis for quantifying the near-surface 3D block structure. In addition, the behavior of the in-situ block system after the excavation is the basis for judging whether to update the construction and support plan.
Traditional scanline surveys provide information pertaining to the frequency of discontinuities, normally over a range of tens of meters. The related processing methods introduced more than 40 years ago (Hudson & Priest 1983) provide estimates of the full range of discontinuity frequency variation, including the directional magnitudes of the maximum and minimum frequencies. The trace length estimation (Pahl 1981) based on window mapping provides a foundation for inferring the area size of discontinuities in 3D space. Fracture system modeling (Dershowitz & Einstein 1998) is a methodology developed to statistically combine geometric characteristics of shape, size, location and orientation of discontinuities as a computer model of the fracture network at a particular location.
