Effect of Matric Suction on Deformation of Gypseous Sand Using Modified Oedometer

Gypsum is a soluble material, and it one of the problematic components in soil west Iraq. Al-Najaf governorates Iraq which suffers from gypsum content different levels. The city mainly sand-sized particles bonded by percentages gypsum. main problem this component dissolution upon wetting process. This paper investigates effect decreasing matric suction (wetting) on deformation under specific stress level. investigation includes three suctions (50, 20, 0 kPa) net normal stresses 221 kPa, 442 kPa 885 respectively. specimens are remolded to 95% maximum dry density proctor test. A modified Oedometer setup used perform tests, including application air water pressures up achieve suctions. results revealed that highest value collapse potential (CP) 221kPa, greatest part CP achieved prior saturation soil. issue must be considered analysis design foundation unsaturated gypseous sandy soils.