Roughness measure of a large in situ discontinuity surface by non-contact survey

Roughness of rock joint surface plays a key role in the stability conditions of rock slopes and it is commonly assessed on small portions of the outcropping surface or laboratory samples. However, roughness is naturally dependent on the considered scale, the analyzed surface sector (surface heterogeneity), and the direction of measurement (surface anisotropy). Therefore, the scale effect, heterogeneity and anisotropy should be quantitatively assessed to understand their role in shear resistance variations. This paper describes the surveys carried out on an extensive natural discontinuity in a slope along the Elva Valley Road (Northwestern Italy) subject to frequent and intense instability phenomena. A digital surface model (DSM) of the entire surface was obtained through UAV (Unmanned Aerial Vehicle) photogrammetric technique and the resulting point cloud was analyzed in order to measure the spatial variability of the surface roughness considering the different directions and the surveying interval.