Abstract Gypseous soils have been widely considered problematic soils due to their unstable and detrimental behaviors, i.e. collapse upon wetting, fabric changes, and excessive settlement. Understanding their behaviors is, hence, essential. This work presents, therefore, a mechanical study into the behavior of a soil at three different gypsum contents (GC) of 4.15%, 14.15% and 24.15%. The experimental program included a series of physical and mechanical tests. Direct shear tests were conducted at different normal stresses. In addition, XRF and XRD tests were performed to investigate the chemical composition and the soil mineralogy. The effect of the GC on the mechanical characterization was significant. The results of the direct shear tests revealed significant changes in shear strength parameters. This was attributed to changes in soil fabrics. Higher shear resistance was obtained at lower GC. The analysis was, then, extended to carry out a parametric study using an upper bound theorem to investigate the effect of GC on the mechanical behavior and failure mechanisms for a strip surface footing. Despite the increase in GC, there was an observed rise in bearing capacity at the critical state. In addition, changes in failure mechanisms were considerable as different failure modes were obtained.
