Repeated lidar acquisitions in an underground salt gallery in the Alsatian potassic basin (France): Monitoring and geomechanical modelling

• Published in: Tunnelling and underground space technology Vol. 123; p. 104406
• Main Authors: Modeste, Guillaume, Masson, Frédéric, Doubre, Cécile, Cornet, François
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.05.2022; Elsevier BV; Elsevier
• Subjects: Coordinates; Deformation; Geomechanical modelling; Geomechanics; Global positioning systems; GPS; Lidar; Mechanical properties; Methodology; Monitoring; Rheological properties; Rheology; Rock salt; Rocks; Salt; Sciences of the Universe; Underground cavity; Underground construction; France; Lidar; Underground cavity; Methodology; Rock salt; Geomechanical modelling
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2022.104406

•• A new methodology is developed to monitor the deformation of underground excavation.•• Lidar device is shown to be a useful tool to characterize the surrounding medium.•• The closure rate of the salt gallery is about 0.2–0.25% per year at 550 m deep. In the Alsatian potassic basin, located northwest of Mulhouse (eastern France), the deformation of an underground salt gallery is monitored from April 2017 to April 2019 using repeated static lidar acquisitions. This monitoring aims to characterize the rheology of the rock salt. The gallery is situated at 550 m deep in a 20 m thick rock salt layer. At this depth traditional referencing tools such as GPS are not available; and the salt is creeping, which prevents the referencing of the measurements with respect to a stable area. First, we develop a specific acquisition protocol to precisely monitor the deformation affecting the gallery walls over time. After two years, we measure a horizontal deformation between 0.10 and 0.30% all along the gallery with a mean uncertainty of 0.08%. From the low horizontal deformation, a new methodology is developed to set the point clouds in the same coordinate system. By doing so, the gallery closure, or volumetric deformation, is calculated. Then, the horizontal deformation time series of the gallery is used to parametrize the mechanical behaviour law of the rock salt, consistent with parameters from laboratory work on this rock salt. Through our work, in addition to the new methodology, the lidar device is shown to be a useful and polyvalent tool to monitor underground cavities and to mechanically characterize the surrounding medium.