GYPSEOUS SAND

This paper presents the results of laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil under various types of loading. The soil samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14 %, 22 % and 29 %. A wetting-process tests were conducted in a modified triaxial cell on these soil. This procedure likes when a structure has been constructed and the degree of saturation of a foundation soil is increased (decreasing in matric suction). Four matric suctions were adopted; 100, 60, 30 and zero percentages of initial matric suction under two different mean net stresses; 100 kPa and 200 kPa. The changes in the degree of saturation may be due to rainfall, water table rising and/or leaking of sewage and water pipes. The results from this path revealed that the volumetric strains are increased with decreasing of the matric suction and increasing of the gypsum content.

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/cm 2). The soil specimen is soaked under three stress levels (1.11, 2.23, and 4.47 kg/cm 2) 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.

The wetting process has great effect on the characteristics of the unsaturated soils. This paper examines the collapse potential due to settlement of the gypseous sand soils upon wetting. The soil samples are taken from Al-Najaf city in Iraq with two different gypsum contents (15% and 29%). The investigation is performed using computerize Oedometer test cell under six stress levels. The effect of soil density is also investigated as a percent of field dry density (100% and 85 %). Initially the tests are started with unsaturated soil samples (water content of 4%), then the wetting process for few minutes (short term) is performed for each stress level to distinguish the effect of wetting on sample settlement-time at each level. The results indicate that there are noticeable increase in the settlement with increase of gypsum content, stress level and decreasing in the soil initial density. Most of the final settlement is accomplished within initial few seconds then the settlement increases in gradual trend. No collapse potential within investigated soil characteristics according to collapse formula in the literature.

This paper presents the results of laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil under various types of loading. The soil samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14 %, 22 % and 29 %. A wetting-process tests were conducted in a modified triaxial cell on these soil. This procedure likes when a structure has been constructed and the degree of saturation of a foundation soil is increased (decreasing in matric suction). Four matric suctions were adopted; 100, 60, 30 and zero percentages of initial matric suction under two different mean net stresses; 100 kPa and 200 kPa. The changes in the degree of saturation may be due to rainfall, water table rising and/or leaking of sewage and water pipes. The results from this path revealed that the volumetric strains are increased with decreasing of the matric suction and increasing of the gypsum content.

This paper shows the different in the volumetric strains between the Oedometer tests with different soaking durations and the unsaturated triaxial tests. The disturbed samples were taken from Al-Najaf city in Iraq. All specimens have the same high gypsum content of 29 %. For Oedometer tests, the specimens are tested in the different soaking durations; the first is in natural moisture content then half hour, one week and two weeks. While in triaxial tests, a wetting induce has been conductive to estimate the volumetric strains under two stress levels (2.5 and 5 kg/ 2) with presence of matric suction in four levels; initial matric suction (ψo), 0.6 ψo, 0.3 ψo and zero ψ. The results from unsaturated triaxial tests indicate that the volumetric strains are increased as matric suction decreased and the trend of stress-strain curve became steep. While from Oedometer tests, when the specimen is soaked in natural and for a half hour, the volumetric strains are not significantly changed and close to the high matric suction. When the soaking time is increased to a one week, there is relatively increase in volumetric strains. But after two weeks soaking in Oedometer cell, the volumetric strains are very clear in increasing and close to the volumetric strains from unsaturated tests in low matric suction.