Amirkabir University of Technology Amirkabir Journal of Civil Engineering 2588-297X 52 10 2020 12 21 Behavior Study of the Gypsiferous Sand Soil of AlNajaf City with Presence of Matric Suction Using Unsaturated Triaxial Device Behavior Study of the Gypsiferous Sand Soil of AlNajaf City with Presence of Matric Suction Using Unsaturated Triaxial Device 2435 2450 3519 10.22060/ceej.2019.16339.6194 FA Mustafa Abdalhusein Civil Engineering Department, Engineering Faculty, Ferdowsi University of Mashhad, Iran Ali Akhtarpour Civil Engineering Department, Engineering Faculty, Ferdowsi University of mashhad,Mashhad,Iran 0000-0003-1654-0194 Mohammed Mahmood Civil Engineering Department, Engineering Faculty, Kufa University, Iraq Journal Article 2019 05 15 Al-Najaf city is considered one of the gypsiferous rich soils cities in Iraq. When a building is constructed on a gypsiferous soil in the unsaturated state, no effective settlement will be distinguished. When a gradual saturation has occurred, the soil gives a clear deformation and may be collapsed. This paper presents how the degree of saturation can affect on the deformation of a gypsum sand soil. A triaxial test device has been modified to have the ability for unsaturated tests. The soil samples were taken from Al-Najaf city in Iraq. Disturbed samples with two different gypsum contents; 14% and 29%, are tested with the presence of different matric suctions, initial matric suction, 60% initial matric suction, 30% initial matric suction and zero matric suction. A loading-path was adopted to symbolize when construction is built on a gypsiferous sand soil in a specific matric suction (specific degree of saturation). In addition to the previous tests, two conventional saturated tests (CD) were added under the above mentioned of confining stresses. The results were when increasing matric suction, the stiffness and shear strength are reduced and the volumetric strains increase significantly. The percentage increases are 60% and 50% under confining pressure of 100 kPa and 200 kPa, respectively for the two selected gypsum contents. The results of this study can be used to estimate the settlement that results from decreasing matric suction due to water table rise or other phenomena. Al-Najaf city is considered one of the gypsiferous rich soils cities in Iraq. When a building is constructed on a gypsiferous soil in the unsaturated state, no effective settlement will be distinguished. When a gradual saturation has occurred, the soil gives a clear deformation and may be collapsed. This paper presents how the degree of saturation can affect on the deformation of a gypsum sand soil. A triaxial test device has been modified to have the ability for unsaturated tests. The soil samples were taken from Al-Najaf city in Iraq. Disturbed samples with two different gypsum contents; 14% and 29%, are tested with the presence of different matric suctions, initial matric suction, 60% initial matric suction, 30% initial matric suction and zero matric suction. A loading-path was adopted to symbolize when construction is built on a gypsiferous sand soil in a specific matric suction (specific degree of saturation). In addition to the previous tests, two conventional saturated tests (CD) were added under the above mentioned of confining stresses. The results were when increasing matric suction, the stiffness and shear strength are reduced and the volumetric strains increase significantly. The percentage increases are 60% and 50% under confining pressure of 100 kPa and 200 kPa, respectively for the two selected gypsum contents. The results of this study can be used to estimate the settlement that results from decreasing matric suction due to water table rise or other phenomena. https://ceej.aut.ac.ir/article_3519_1fd7b875d3473501d1b771ebe934ca59.pdf