Derivation of space-resolved normal joint spacing and in situ block size distribution data from terrestrial LIDAR point clouds in a rugged Alpine relief (Kühtai, Austria)

Abstract

Terrestrial laserscan (TLS) surveys allow the geological investigation of rock slopes, which cannot be measured by direct surveys because of inaccessibility, high hazard potential or excessive effort. The normal joint spacing and the in situ block size distribution are relevant properties for rock mass characterisation but are commonly evaluated statistically or at small regions only. This study presents the jointing characterisation of an Alpine rock slope by both scanline data and a new, automated analysis of point cloud data. The slope, located in the Langental (Austria), is characterised by a rugged Alpine relief and granodioritic gneisses fractured by non-persistent joints. The scanline data and the TLS surveys were used to investigate joint set orientations, normal joint spacings and in situ block sizes. Area-wide maps of rock slope properties were prepared from the results of the point cloud analysis. The general results derived from the point clouds are in good agreement with the scanline data. The space-resolved maps show larger block sizes in some of the higher ranging sub-regions and small block sizes in tectonically formed gullies, as well as various local variations. These visualisations are much more beneficial for most rock mechanical questions than common statistical data evaluation approaches using pre-defined sub-regions, which are treated as homogenous areas and thus are missing space-resolved information.