Long time swelling of anhydritic rocks: Mineralogical and microstructural evaluation

In tunnel engineering clay sulfate rocks cause problems due to their notorious swelling behaviour. Field and laboratory measurements often give contradictory indications of the magnitude of swelling pressures (0.5-2.5 rsp 0.5-7MPa). To determine the fabric dependency of the swelling behaviour of anhydritic rocks, free swelling and swelling pressure tests were performed on specimens taken from different orientations relative to the bedding plane. Prior the test the anhydrite content was 65%. By the end of the free swelling strain test after 1 year 21-78% of anhydrite was transformed into gypsum. Free swelling heave correlates strongly to the fabrics of the starting material. The measured free swelling heave of…