This paper investigates the effect of the soaking process on gypseous sand soils. The recent research investigates the time-based soaking method on high gypsum contents (29%) of soil samples. The softening of gypsum materials upon wetting process leads to break the bonds of the soil particles and the settlement of structures will be occurred. The settlement value and rate are the basic problems for the geotechnical engineers. The samples of this investigation have been collected from the selected site in Al-Najaf city in Iraq, then these samples are remoulded to the density of 85% of the maximum dry density from Proctor test and moisture content of 4% in the cell of the computerized Oedometer device and under different stress levels (1.11, 2.23 and 4.47 kg/cm2). The soil specimen is soaked under three stress levels (1.11, 2.23, and 4.47 kg/cm2) separately. The results revealed that with increasing of soaking periods and stress level, there is increasing in collapse potential of such soils. The collapse potential was increased from <1% after half-hour soaking to about 8% after two-weeks of soaking.

This study looks into the in uence of matric suction on the volume change of gypsum sand soil in unsaturated conditions. The specimens were collected from Al-Najaf, Iraq, and included 14-percent and 29-percent gypsum. Three series of initial stress of laboratory tests were utilized in a modi ed Oedometer device. For each gypsum content, twelve remolded specimens were examined in unsaturated circumstances with the initial stress and applied stress using four matric suctions (30 kPa, 18 kPa, 9 kPa and saturated state). Three tests were performed for each matric suction with initial stresses, no initial load, 56 kPa and 112 kPa, respectively. The ndings of unsaturated tests along the wetting path in terms of nal volumetric strain show a clear pattern of increasing in vertical strain as gypsum content rises and matric suction reduces under a variety of situations. The wetting process softens the gypsum components, resulting in an increase in vertical strains.

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This study looks into the influence of matric suction on the volume change of gypsum sand soil in unsaturated conditions. The specimens were collected from Al-Najaf, Iraq, and included 14-percent and 29-percent gypsum. Three series of initial stress of laboratory tests were utilized in a modified Oedometer device. For each gypsum content, twelve remolded specimens were examined in unsaturated circumstances with the initial stress and applied stress using four matric suctions (30 kPa, 18 kPa, 9 kPa and saturated state). Three tests were performed for each matric suction with initial stresses, no initial load, 56 kPa and 112 kPa, respectively. The findings of unsaturated tests along the wetting path in terms of final volumetric strain show a clear pattern of increasing in vertical strain as gypsum content rises and matric suction reduces under a variety of situations. The wetting process softens the gypsum components, resulting in an increase in vertical strains.