Flow in Geo-materials

Soils are Mother Nature’s products and their composition is quite complex. Typically soils are composed of three phases: solid, water, and air. When soils are under the water table, they are inherently saturated. Under the water table, air voids in the soils are completely filled with water, and the soils are essentially two phase materials. Above the water table, there are mixtures of air and water in the voids and the soils are three phase materials. This multi-phase nature of soils develops the coupled behavior of their constituents. A simple example of coupled behavior is the stress distribution of a composite beam such as a reinforced concrete beam. The reinforcing steel carries greater stress than the concrete due to its higher modulus. In soils, the phases as well as moduli of their various constituents are different. Therefore, additional coupled behavior from different phases is expected in addition to that from the different moduli. The coupled behavior from the different phases involves the flow characteristics of pore liquids (e.g. air and water). Traditional coupled theories of mixtures (Biot 1956b, Prevost 1980) address the effects of pore liquid flow; however, more recent coupled theories of mixtures address the additional coupling with rate dependency and micro-mechanical mechanisms such as grain rotations, grain interactions, and damages Voyiadjis and Song (2005a).