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)
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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 Längental (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.
KeywordsTerrestrial laserscan Point cloud analysis Joint characterisation Normal joint spacing In situ block size distribution Austria
The authors thank TIWAG-Tiroler Wasserkraft AG for providing the Riegl TLS scanner and archive data. We thank Heiner Rett for support during the TLS field surveys, and Christian Zangerl and Christoph Prager for fruitful discussions. This study was part of the alpS research project AdaptInfra, which was supported and funded by TIWAG-Tiroler Wasserkraft AG, ILF Consulting Engineers Austria GmbH and the Austrian Research Promotion Agency (COMET program). The alpS-K1-Centre is supported by Federal Ministries BMVIT and BMWFW and by the states of Tyrol and Vorarlberg within the framework of the Competence Centers for Excellent Technologies (COMET). COMET is processed through FFG (Österreichische Forschungsförderungsgesellschaft).
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