One-year Monitoring and Digital Image Analysis of In-situ Desiccation Cracks on Tournemire Argillite Rock

Abstract

Digital image correlation was used for the first time in an underground gallery to monitor the argillaceous rock deformations during an annual climatic cycle. This experimental in situ investigation was carried out on a study area of 34.4×27.5 cm², located on the East96 gallery front at the Tournemire experimental station, during which the relative humidity (RH) and temperature (T) were continuously measured for more than one year and fluctuate naturally.Our results demonstrate the ability of the non-invasive DIC method to monitor clay-rock strains and the opening and closure of desiccation cracks. Moreover, our study provides the following results. First, the hydric strains were anisotropic; the strains perpendicular to the desiccation cracks were almost homogeneous and much larger than those parallel to the same cracks. Second, the changes in crack apertures calculated from the displacement fields and the strain fields were clearly correlated and concomitant with changes in RH and T. Third, contrary to direct measurements acquired at the Mont-Terri site, the crack apertures of the desiccation cracks were reversible after one year of data acquisition. Moreover, although the main desiccation cracks were sub-horizontal and associated with the direction of bedding planes, our work demonstrated the existence of sub-vertical cracks.