Unsaturated behaviour of gypseous sand soils using a modified triaxial test apparatus

Abstract

ABSTRACT This paper presents laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil. The samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14%, 22%, and 29%. Two series of laboratory tests were conducted. The first one is loading-path likes when a building is constructed on these soils in a specific degree of saturation (specific matric suction). Four matric suctions were adopted; 100, 60, 30, and zero percentages of initial matric suction under two confining stresses; 100 kPa and 200 kPa. Also, two saturated tests (CD) were performed under the aforementioned confining stresses. The second method is wetting-path, likes when a structure has been constructed and the degree of saturation of a foundation soil increases (decreasing in matric suction). The results from both paths revealed that the volumetric strains were increased by decreasing the matric suction and increasing the gypsum content..