Hydro-mechanical modeling of swelling processes in clay–sulfate rocks: comparison of swelling laws

Swelling of clay-sulfate rocks is a serious problem in geotechnical projects. In Staufen (a city in Baden-Württemberg, Germany), the heave of the land surface occurred as a result of clay-sulfate rock swelling, triggered by water inflow in Triassic Grabfeld Formation (formerly Gipskeuper = “Gypsum Keuper”). Clay-sulfate swelling is controlled by clay swelling due to osmotic processes, combined with chemical swelling due to the transformation of anhydrite into gypsum, associated with a volume increase. Previous studies showed that hydro-mechanical (HM) models can be employed to determine the mechanical behavior of swelling rocks with an accuracy sufficient for planning remedial measures. In such models, a constitutive relation between swelling pressure (stress) and swelling deformation (strain) must be defined (“swelling law”). In the present study, we developed coupled HM models to reproduce the heave observed at the Staufen site. We implemented different swelling laws, namely linear, semi-logarithmic, and sigmoidal constitutive relations between stress and strain. We compared the model calculations with the measured long-term heave records at the study site. We then analyzed the errors associated with each modeling approach to evaluate its effectiveness. This contribution provides insights about the performance of three existing swelling laws to estimate the long-term mechanical behavior of clay-sulfate rocks.