Study on the geological and engineering aspects of anhydrite/gypsum transition in the Arabian Gulf coastal deposits

Evaporitic geology, hot and arid climate, fluctuating relative humidity, and an alkaline environment governed the evolution of sedimentary deposits in the Arabian Gulf coast. Calcium sulphate generally occurs as anhydrite in the unsaturated surface layer of local soil formations. Anhydrite hydrates to gypsum with an associated volume increase of up to 63%, whereas gypsum dehydration results in a reversal back to anhydrite that leads to 39% volume decrease. Swelling and compressibility problems are common in several coastal deposits of the globe. This paper investigates the geological and engineering aspects of anhydrite/gypsum transition in the Arabian Gulf coast. Oedometer test results on Dammam anhydrite were studied in conjunction with morphological assessments at critical volume change stages. Results indicated 10% swelling potential and 295 kPa swelling pressure for hydrating anhydrite. The compression index of anhydrite and gypsum were 0.067 and 0.12, respectively, whereas the rebound index of anhydrite was 0.023.