Effect of Wetting Process with Presence of Matric Suction on Unsaturated Gypseous Sand Soils

Abstract

This paper presents the results of laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil under various types of loading. The soil samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14 %, 22 % and 29 %. A wetting-process tests were conducted in a modified triaxial cell on these soil. This procedure likes when a structure has been constructed and the degree of saturation of a foundation soil is increased (decreasing in matric suction). Four matric suctions were adopted; 100, 60, 30 and zero percentages of initial matric suction under two different mean net stresses; 100 kPa and 200 kPa. The changes in the degree of saturation may be due to rainfall, water table rising and/or leaking of sewage and water pipes. The results from this path revealed that the volumetric strains are increased with decreasing of the matric suction and increasing of the gypsum content.

Characterization of collapsible gypsum sand soil with the presence of matric suction using a modified odometer apparatus

“…Rainfall, rising water tables, and/or sewage and water pipe leaks could all contribute to variations in saturation levels. The volumetric strains grow as the matric suction decreases and the gypsum content rises, according to the results of this approach [12].…”

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

“…Gypseous soil is collapsible soil that causes problems to buildings and structures constructed on them due to a significant decrease in the shear strength as they are exposed to wetting [6,7]. This collapse depends on many factors, such as the wetting process [8][9][10][11], higher gypsum content, void ratio, permeability [12], initial degree of saturation [13,14] and soil time-based wetting prior loading [15][16][17]. Gypseous soils experience numerous changes in their physical and mechanical characteristics due to their exposure to continuous mass loss [18].…”

Reliability of Shear-Box Tests Upon Soaking Process on the Sand Soil in Al-Najaf City

“…There is a noticeable increase in settlement upon different soaking durations on Al-Najaf city soil using the Oedometer test [22,23]. There is an obvious effect of wetting on increasing of soil deformation in unsaturated tests using a modified triaxial device [24,25]. Recent evidence recommends that there is a decreasing in the shear strength parameters (φ) of the Al-Najaf city soil and bearing capacity under saturated testing when the soil was subjected to the different soaking periods [26].…”