Drying-induced shrinkage of Boom clay: an experimental investigation

Drying-induced shrinkage of geomaterials may have a strong effect on geostructure stability and deformation. The settlement of foundations and fracture openings in slopes, roads, and tunnel walls may be due to drying shrinkage. However, there is still a lack of knowledge concerning shrinkage evolution with time and shrinkage propagation within the material. In this study, the shrinkage of a specific clayey rock - Boom clay - under drying conditions is investigated experimentally. This rock is a deep geological formation, which is under study for high-level and long-term radioactive waste storage in Belgium. Two experimental campaigns are presented. The first, based on the vapour equilibrium drying technique and coupled with sample size manual measurement, aims to characterize the material shrinkage in balanced states. The second, based on the convective drying technique and coupled with shape monitoring using X-ray tomography, aims to analyse how shrinkage develops before reaching a steady state. Both approaches put in evidence the shrinkage anisotropy of this structurally bedded rock, with a ratio around 2 between the direction of maximum strains and the direction of minimum strains. However, the two drying techniques also provide complementary results as the relation between the amount of shrinkage and the retention curve (for uniform drying imposed with saline solutions) and the kinetics of shrinkage propagation inside the material (for nonuniform drying imposed with air convection).