University of Twente Student Theses


Rockfall susceptibility assessment on UAV based 3D point clouds

Seabra Nogueira Alves Albarelli, Daniel (2020) Rockfall susceptibility assessment on UAV based 3D point clouds.

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Abstract:Rockfall is a common geological hazard in mountainous areas causing economic and human losses when fallen blocks impact infrastructure and communities along its way. A key aspect on the mitigation of such losses starts by identifying in a rock slope (or cliff) the source areas where blocks are more likely to detach and generate rockfalls. This is the aim of the Rockfall Susceptibility Assessment, which constitutes the initial step for the following Hazard Assessment, such as estimation of block volume and rockfall simulation (trajectory, energy, rebound height). Geomechanical properties of rock mass play a major role especially for local assessments since discontinuity geometry and orientation largely govern the rock mass quality and stability. Due to recent advances in remote sensing techniques, rock mass characterization is shifting from the traditional labor-intensive field surveys to the 3D point cloud environment, where accurate, abundant and high-resolution geometric information can be retrieved. Unmanned Aerial Vehicle (UAV) has been used as a platform to acquire RGB photographs of rock slopes and, through the photogrammetric method of Structure from Motion, generate 3D point clouds (3DPC). Nevertheless, the application of this technology to Rockfall Susceptibility Assessment is still in its early developments and there is a lack in the literature on methodologies tailored for application to UAV. This thesis presents a comprehensive and novel methodology to fill this gap. It consists of 4 major sequential blocks: (i) ) use of UAV photogrammetry with data acquisition to 3DPC generation, (ii) Feature extraction for rock mass characterization in which joint set orientation, persistence, spacing and block volume are obtained, (iii) Slope Stability Assessment by applying the extracted features firstly in Rock Mass Rating (RMR), followed by Slope Mass Rating (SMR) for each joint set and (iv) development of indicator for spacing, persistence, overhanging and SMR indexes, followed by their integration for a Rockfall Susceptibility Index. This methodology was tested to a road cut rock slope of approximately 46 m lateral extension and 14 m height in a mountainous area of the Samaria Gorge National Park, in Crete Island (Greece). Visual validation shows that areas of higher and moderated rockfall susceptibility on the rock slope correspond to source location from where the bigger and highest number of fallen blocks were found on the foot of the slope. Hence, this approach helps to refine the identification of potential rockfall source areas, which are areas prone to rock detachment compared to their surroundings and to improve the input for hazard assessment, including rockfall run out simulations. Additionally, the methodologic workflow contributes to the following innovations on 3DPC: Rock Quality Designation (RQD) index estimation, visualization of spacing, persistence and SMR index, semi-automatic block volume calculation for regularly shaped blocks formed by flat exposed surfaces on the rock mass, the persistence of overhanging enabling the distinction on the extension of lack of support and thus an indicator of greater volume susceptible to rockfall.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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