Assessing Dispersivity and Expansivity of Clay Soils in the South-East of Yazd with Aim of Investigating Correlation between Them

Having knowledge about physical, chemical and mechanical properties of problematic soils is necessary when they are applied in construction projects as borrow materials or foundation, because these soils have potential to create large financial losses. This research deals with characterizing dispersive and swelling soils as problematic soils in southeast of Yazd (center of Iran) with aim of establishing a relationship between dispersivity and expansivity indices. In this regard, after performing a series of physical and chemical tests, the characteristics of the soil samples were determined, and their dispersivity degrees were specified by conducting chemical, pinhole and double hydrometer tests. Also, swelling rates of the soils were estimated using direct method (modified free swell index, MFSI) and indirect methods (different criteria developed for swelling assessment). The results showed that chemical parameters overestimate dispersivity of the soil samples (dispersive to semi-dispersive) in compared to pinhole and double hydrometer tests (slightly non-dispersive to moderately dispersive). Different expansivity degrees were defined using the direct and the indirect methods (ignorable to very high) for the soil samples. Among the empirical criteria used to evaluate the swelling potential, the AASHTO's criterion has the closest results to the MFSI in the both boreholes. Also, it revealed that as depth increases, the degree of soil dispersivity and expansivity decrease in response to the reduction of fine grain content in the samples. Finally, the correlations between dispersivity and expansivity indices, showed that sodium absorption ratio (SAR) can be used as a reasonable index to estimate soil swelling potential.