Qualitative assessment of surface roughness of limestone specimens from the orientation of unwrapped triangulated point clouds

Abstract

Weathering reduces both the strength and stiffness of rock. Since weathering is a surface phenomenon it can be assessed using surface imaging techniques. The surface roughness of twelve cylindrical limestone specimens from Florida were assessed using analysis of close-range photogrammetry. Dense point clouds produced from the specimens were unwrapped and triangulated using Delaunay triangulation. Outward normal facing vectors were computed for each triangle and the γ-values were assessed. Smooth surfaces had lower average γ-values and lower standard deviations than rough surfaces. Surface roughness could easily be distinguished using lognormal probability density functions based on average and standard deviation of the γ-values. For smooth specimens, histograms of γ-values were similar to the probability density functions. However, for rough specimens the histograms of γ-values were not similar to the probability density functions. The histograms for the roughest specimens showed a bimodal distribution of values with peaks at both the low and high ends of the histograms.