Modelling the degradation and swelling of clayey rocks bearing calcium-sulphate

► A heave mechanism involving gypsum crystal growth in discontinuities discussed in detail. ► A novel formulation of the phenomenon, consistent with field evidence and physic-chemical basic principles. ► A fascinating and well instrumented case history involving rock swelling after tunnel construction in sulphated tertiary clayey rocks. Extreme heave and pressures recorded in time. ► A discussion of the factors controlling gypsum-induced swelling. Field data well interpreted. ► New results of considerable practical importance derived from the analysis. For instance, the calculation of the maximum attainable swelling pressure against rigid linings.