Fine gypsum soils, when saturated and loaded, because of their high porosity, have large settlements. Compaction of the soil and removal of the load causes the soil to swell. These properties of gypsum soils cause many problems for structures built on them. For instance unsymmetrical settlement, uneven ground floor and cracks in façade are some of the problems. Likewise in road engineering, swelling of this type of soil located under the asphalt after absorbing water is one of it most important problem. So realizing and identifying the behavior of gypsum soils and effort in finding solutions for decreasing the amount of settlement and swelling are the main objectives of this study. The soil samples were from the City of Mashhad, which is the second largest city in Iran. These soils naturally contain high amount gypsum and hence have a special behavior. In this study, samples with different amount of gypsum were gathered and classified to seven sample groups. Preliminary tests done showed that the increase in the amount gypsum causes the soil plasticity index and unit weight to decrease, which in turn increases settlement. In order to investigate the influence of degree of compaction, all samples were compacted with different unit weight and the swelling potential and swelling pressures were measured after saturation. The results show that with increasing unit weight and amount of gypsum, the soil swelling potential increases. Cycles of wetting and drying and also cycles of loading and unloading were performed to investigate their influence on the gypsum soil
