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Accueil du site → Doctorat → Royaume-Uni → 2013 → Effect of gypsum on the hydro-mechanical characteristics of partially saturated sandy soil.

Cardiff University (2013)

Effect of gypsum on the hydro-mechanical characteristics of partially saturated sandy soil.

Ahmed, Khalid Ibrahim

Titre : Effect of gypsum on the hydro-mechanical characteristics of partially saturated sandy soil.

Auteur : Ahmed, Khalid Ibrahim

Université de soutenance : Cardiff University

Grade : Doctor of Philosophy (PhD) 2013

Gypsum rich soils are of wide occurrence in the Middle East. They cover large areas of Iraq. Gypsum is one of the moderately soluble salts that can have significant effect on the engineering properties of soils. The effect of gypsum content and the stress state on the main hydraulic functions, volume change, shear strength and deformation characteristics of unsaturated silty clayey sand were experimentally examined. Statically compacted specimens of synthetic sand-gypsum mixtures were used. A new stress controllable pressure plate device was developed. The modified device was used to establish simultaneously both the stress-dependent soil-water characteristic curves (SD-SWCCs) and the stress-dependent hydraulic conductivity functions (SD-HCFs) during drying and wetting paths. The test results revealed that the parameters of the drying SWCC such as the water holding capacity, the air-entry suction, the air-entry water content, and the residual suction are clearly increased with increasing gypsum content. Same effect of gypsum was noticed on the wetting SWCC parameters. A clear decrease in saturated water content, desorption rate, absorption rate, and water holding capacity with increasing the applied net normal stress was noticed. Transient outflow methods were used to measure the SD-HCFs. An increase in the SD-HCFs with increasing gypsum content was found. Clear hysteresis effects on k(ψ) and minor hysteresis on k(w) were noticed. It was found that the outflow methods can be applicable between the air-entry suction and residual suction only. Direct shear tests were carried out on saturated and unsaturated specimens. The unsaturated specimens were air-dried and tested under constant water content conditions. Matric suction values were evaluated by incorporating the SD-SWCC test results. The friction angle related to matric suction (b), the effective stress parameter (χ), and the suction stress (s′) were found clearly decrease with increasing gypsum content and with increasing the net normal stress level. However, test results of saturated specimens revealed that the effective shear strength parameters (′, c′) are noticeably increased with increasing gypsum content in the soil mixture.

Mots clés : Gypsiferous soils ; Stress dependent SWCC ; Unsaturated hydraulic conductivity ; Unstaurated shear strength ; Soil-water characteristic curves ; Shear strength and deformation characteristics ; Modified stress controllable pressure plate device


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