Shear Strength of Gypseous Soil under Soaking Conditions

Abstract

Gypseous soil has far been considered one of the metastable soils as it experiences good strength parameters when dry, but upon indentation under goes a sadden-radical decrease in volume, or collapse potential. This will result in great distress in engineering facilities resting on it. This type of soil exists in many regions in world including Iraq, and problems associated with dealing with soil, in general, are numerous in this country. This soil, in its totality, is sandy type, as such its main dominating strength parameter is the friction angle and in special circumstances the apparent cohesion, which may exist. This research is concerned in studying the change in shear strength before and after soaking for gypseous soil. An extensive work is carried out to locate gypseous soil locations in Iraq from available site investigation reports. As such, twelve samples are brought from twelve different locations in Iraq as to be investigated. Test results reveal that there is much data scattering between the soaked and non-soaked angle of friction from one side against the collapsibility and gypsum content for the other side, and the relationship is inversely proportional. There is a decrease of 2-3 degrees in the friction angle as the soil is soaked for 24 hours. The Procter maximum dry density and the specific gravity of soil is inversely proportional to the collapse potential and the data scattering is low. The sieve analysis for the twelve soil samples are sandy in nature.