Laboratory experiments on swelling due to crystal growth in sulphate argillaceous rocks

Crystal growth is a frequent cause of expansive deformations in natural soils, compacted soils, rocks and concrete. The sulphate crystallization in discontinuities and cracks due to evaporation of highly mineralized solutions can contribute in an important way to displacements and swelling pressures that usually appear in tunnels and deep foundations in argillaceous rocks. The present work is aimed to study the basic mechanisms that control the hydrated sulphate mineral growth in anhydritic-gypsiferous argillaceous rocks due to the evaporation of groundwater. The paper presents some laboratory works including mineralogical and micro-structural analysis, as well as the design and development of new free swelling tests which were developed focusing on the capacity to discern the role carried out by the geochemical properties of the water, the main environmental variables and the degree of cracking on undisturbed sulphate argillaceous samples from different zones of the Lower Ebro Basin (Catalonia, Spain).