Towards cavity-collapse hazard maps with Zeb-Revo handheld laser scanner point clouds

Abstract

Underground cavities are ubiquitous across northern Europe's cities and countryside due to a long history of mining and building-stone extraction. Management of cavity-collapse risks requires detailed knowledge of a cavity's geometry, depth and rock-mass characterisation. Current mapping practices are neither sufficiently accurate, detailed nor cost-effective in underground settings. Here, a GeoSLAM Zeb-Revo handheld mobile laser scanner was tested. Its point clouds reproduced planes faithfully (RMS < 10 mm) over typical gallery dimensions (<10 m) and any survey horizontality defect was not measurable. In well-structured corridor networks, reference distance inaccuracy arising after a 115 m loop and 5·25 minutes of instrumental drift did not exceed 3 mm over 30 m (1:10 000) and the difference from the reference length was insignificant. Applied to mapping 11 ha of a disused underground stone quarry in the Paris Basin, Zeb-Revo surveys produced accurate (<1 m) base maps adequate for regulatory cavity hazard maps at 1/5000 scale. Geometric knowledge of accessible cavities is therefore no longer a challenge for collapse hazard mapping.