An Investigation of The Effect of in-Soil present Gypsum and its Leaching on the Strength Properties in Clay Soils



Gypsum found in the soil beneath the foundation of structures, specially hydraulic structures, can cause serious damage to them. The mechanical behavior of gypsiferous soils has not so far been investigated in detail except for the works of Petrukhin (1993). Here, it has been tried to investigate the mechanical behavior and the effect of soil being leached on settlement and strength of these kinds of soils. A non-gypsum containing kind of natural soil was provided from “Moghan” area. The soil was classified as “CH”, according to the Unified Soil Classification System (USCS). The artificial gypsum containing soil samples were prepared by mixing the soil with different contents (in percents of 5, 10, 15, 20, 30, 40) of natural gypsum. Such experimental tests as Grain size distribution, Atterberg limits, Uniaxial test, CBR test and settlement (before and during) were carried out on gypsum containing soil samples according to the ASTM Standard. The results revealed that the existence of gypsum in the soil can cause: Reduction of Atterberg limits, increase in optimum water content and decrease in dry soil density, increase in settlement due to soil being leached and a reduction of the soil strength, specially during the leaching process.