Evaluating Erodibility of gupsiferous soils of Masjed Soleyman petrochemical plant site with emphasiss on dispersive and solubility

Dispersivity is a physico-chemical phenomenon whereby clay soil particles lose their cohesion in the presence of water and repel each other, so that the particles become suspended in water and easily washed with very little energy from the environment. Potential dispersivity in a given soil depends on several factors, including: type of clay minerals, pH, organic matters, temperature, moisture percentage, type and concentration of ions existing in the soil pore water and the characteristics of eroding fluid and usually there are high amounts of sodium cation. Soil dispersivity evidence can be alluded to the development of erosional shapes on steep and flat areas; since these erosional shapes were observed upon the Gachsaran formation in Masjed Soleyman petrochemical site, so sampling was carried out from different parts of the site in order to assess the causes of erosion. Then, by performing physical and chemical tests as well as the tests to characterize soil dispersivity, it was observed that the amount of sodium cation is low and soil itself is non-dispersive. By observing the gypsum mineral, voids and free spaces available in manual and microscopic samples, their gypsum content was determined. Again, by its relation with field observations, it was revealed that erosion shapes induced by leaching, dissolution and ultimately the soil to be hollowed in the result of gypsum mineral presence that has been contributed in developing a kind of mechanical erosion in the region.