Effect of saturation on dynamic characteristics of collapsible gypseous soil using cyclic triaxial testing

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Studying the unsaturated gypseous soils behavior may lead to more understanding of the gypseous soil problems associated with unsaturation under the effect of the vertical vibrations. The purpose of this paper is to assess the suitability of unsaturated gypseous soil as a machine foundation soil. Moreover, such a purpose is considered beneficial in assessing appropriate methods for studying the characteristics and the behavior of unsaturated gypseous soils such as soil elastic modulus parameters, compressibility parameter, waves velocities, and amplitude axial strain for cyclic loading parameters under different with degree of saturation. The tests were performed for conditions 35% and 70% relative density of natural gypseous soil under 1.0 Hz and 2.0 Hz cyclic frequency at degrees of saturation (30%, 60%, and 80%), and fully saturated gypseous soil to investigate the gypseous soil behavior. It was found the values of the elastic modulus and wave velocities at degree of saturation 60% for different number of cycles and frequency increased with decrease of the strain and compressibility. Then, it began to decrease gradually at the saturation degree 80% and 100%, respectively. The best results based on strength consideration were obtained at 60% saturation, and the lowest strength was found when the soil was 100% saturated, for both load frequencies 1, and 2 Hz. The load frequency 1 Hz gave higher values than cyclic frequency 2 Hz of elastic modulus and wave velocities, while the number of cycles was less at the same time and for different degrees of saturation.