Reliability of Soil Water Characteristics Curve under Different Normal Stresses for Unsaturated Sand

¹ Structures and Water Resources Eng. Dept., University of Kufa, Iraq
² Civil Eng. Dept., University of Kufa, Iraq
³ Civil Eng. Dept., University of Kufa, Iraq
⁴ Ph.D., Dept. of Building and Construction Technology Eng., Al-Furat Al-Awsat Technical University

^* Corresponding author: mustafam.alesawy@uokufa.edu.iq

Abstract

The soil water characteristics curve (SWCC) demonstrates a link between soil moisture content and suction. The SWCC is almost treated as an index parameter in unsaturated soil. The soil permeability and shear strength can be linked to SWCC. SWCC is established using filter paper for the wetting path. This paper compares SWCC for both cases stress-dependent and no stress (reference) in the wetting path. The samples of soil are brought from Al-Najaf City with a gypsum content of 29%, Iraq. The stress-SWCC is studied using a modified Oedometer cell with controlled water and air entrance to apply a specific matric suction. While the reference SWCC is estimated using the filter paper method. Matric suction is conducted at a range of pressures from 90 kPa to 0 kPa. The tests use three net normal stresses of 100, 200, and 400 kPa. The results show that there are decreasing values of the SWCC with increasing normal stresses. An interesting result is that this decrease is high and has zero matric suction. The water entry value (WEV) with the most significant value of the water entry change is represented by the matric suction of 50 kPa.