Effect of Saturation and Cementation on the Stiffness of Gypsiferous Soils

Gypsiferous soils are found in several arid regions of the world and are known to cause structural hazards due to their collapsible nature. The collapsibility of gypsiferous soils is dependent on a number of soil parameters and gypsum content is one of the key factors. Gypsum acts as a weak cementing agent in the soils. In terms of macroscale procedures for site suitability investigations, the non-destructive testing methods, using shear-wave velocity measurements, are valuable to quickly characterize the stiffness properties of the sites and subsurface soil conditions. In this study, free-free resonant column testing was used to study the shear-wave velocity patterns of reconstituted specimens of sand and gypsum under different degrees of saturation. An overall increase in stiffness was observed with decrease in degree of saturation. The rise is stiffness was attributed to a combination of cementation and matric suction processes. Cementation was observed in specimens containing gypsum. For soils with less than 30% gypsum content, matric suction was a dominant factor in increasing the stiffness of the soil and cementation effect was not very strong. For soils with gypsum content of 30% or more, an appreciable amount of cementation was observed and matric suction showed little impact. The peaks in shear-wave velocity caused by matric suction were replaced by a plateauing feature. Using the soil water characteristic curve approach, regression relationships were developed to determine the contributions of matric suction and cementation toward the change in stiffness of the soils. The results from this study can be used to predict the stiffness behavior and gypsum content of gypsiferous soils in the field.