Investigating Parameters Affecting the Settlement of Gypsum Soils

Consolidation and stability of soil is influenced by the presence of minerals in the soil and it is especially related to its moisture which is prevalent difficulty in the construction of irrigation and drainage networks. In this research, the effect of natural gypsum on the physical properties of silty soil and its settlement was studied. In order to achieve answers which comply with the conditions of operation, samples were collected from the construction site, containing natural gypsum in soil. Samples were selected, based on a weighted combination of soil and natural gypsum, with percentages of 1%, 4%, 10% and 15% and by conducting standard chemical tests to determine the percentage of gypsum and some general properties of soil were determined. In order to assess the rate of dissolution, consolidation test was also conducted and in this process EC was measured for a month in outlet water samples extracting from the process of replacing distilled water, in a one-day period and under the stresses of 0.25, 0.5, 1, 2, 4 and 8 kg/cm2 in the consolidation device. The results showed that by increasing the amount of gypsum, plasticity index and dry density of soil samples have decreased, but permeability and settlement rates was increased. Since in the calculation of settlement of gypsum-containing soils, parameters such as volumetric compression ratio and stress are also effective, an emperical formula was developed for predicting relationship between consolidation pressure, percentage gypsum and consolidation coefficient.