Preliminary Study on the Reduction in Shear Strength Parameters of Gypseous Soil upon Wetting

Abstract

The main aim of the study is to provide a preliminary formula to estimate the reduction in shear strength parameters of gypseous soil exhibited when soaked in water. Experimental work has been conducted using direct shear test on undisturbed samples with three different gypsum contents 4 %, 28 %, and 42 %. Three different cases were considered, first is soil with its field water content (semi-dry), second after soaked with kerosene, and third after soaked with distilled water. The kerosene was used for comparison purposes substituting water for non-gypseous soils because it has low chemical interaction with gypsum. For semi-dry cases, results show proportional relationship between peak shear strength and gypsum content. However, the opposite holds true once submerged with water in which soil cohesion fades and the frictional angle is reduced to 72 %, 56 %, and 52 % respectively for the given gypsum content. A formula has been proposed that can be used by practitioners to estimate the reduction in the frictional angle based on the gypsum content of the soil.

Keywords

• gypseous soil
• direct shear
• soaked soil
• shear strength
• kerosene