The behavior of materials which is used in projects is a function of physical and geochemical characteristics. Development of civil infrastructure is necessary for the development of human society and their success depends on a variety of issues, including understanding the project environment, estimating the right parameters, and predicting material behaviors. Soil material is used in various project such as earth dams, roads, basement of irrigation pipe lines, etc. the behavior of these material in addition to their physical properties, depends on their chemical properties which lead to special complexity. Whenever other materials such as gypsum, encounter to clay, it doubles the complexity of their behavior and use of them will be problematic. Defining the minerals and compounds of these soils is necessary to a correct judgment about them. Kalar city is located in south east of Kurdistan region in Iraq and is known as center of Garmian area. Geological formations such as Lower Fars and Upper Fars, which can be seen in these are include gypsum, thus their eroded products is found in plains with fine garians. On the other hand, these areas are the site of various projects that may use materials in the area, so it is necessary to study the chemical and engineering properties of these materials and the impact of gypsum compounds on them. In this study, by sampling from different location, the chemical composition of soils using XRD & XRF analysis and their properties such as size distribution by sieve analysis and hydrometry, soil class, plasticity properties, compaction parameters and shear strength parameters were obtained. Then, by adding gypsum and changing the chemical composition of the soil, its effect on shear strength parameters was investigated.
