Behavior Study of the Gypsiferous Sand Soil of AlNajaf City with Presence of Matric Suction Using Unsaturated Triaxial Device

Document Type : Research Article

Authors

1 Civil Engineering Department, Engineering Faculty, Ferdowsi University of Mashhad, Iran

2 Civil Engineering Department, Engineering Faculty, Ferdowsi University of mashhad,Mashhad,Iran

3 Civil Engineering Department, Engineering Faculty, Kufa University, Iraq

Abstract

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.

Keywords

Main Subjects

References

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Amirkabir Journal of Civil Engineering
Volume 52, Issue 10
January 2021
Pages 2435-2450

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