Application of unsaturated soil mechanics for agricultural conditions

Agricultural engineers often draw upon the classical theories of soil mechanics in their study of agricultural soil behaviour. These theories are largely based on the assumption that the soil is saturated. In an emerging theoretical framework, an unsaturated soil is considered to have four phases: solid, air, water, and contractile skin (the air-water interphase). The contractile skin acts like a rubber membrane as it induces a matric suction in the soil pores. Suction has been shown to affect both strength and volume change characteristics of unsaturated soils. The relationship between water content and matric suction (the soil-water characteristic) becomes an important component of the unsaturated soil mechanics framework. In this paper, concepts and implications of these developments for some agricultural shear strength-based models are discussed. Experimental data highlighting these relationships are also presented.