Effects of inter-phase mass transfer in heated clays: A mixture theory

Saturated clay soils consist of an assemblage of clusters of platelets which with other non-clayey particles form the soil matrix with voids filled with water. Electro-chemical forces attract water firmly to the clay platelets, forming a water layer which is not able to flow under normal conditions. This kind of water is referred to as the firmly adsorbed water. The rest of water (called bulk water) is able to flow under sufficiently high pressure gradient. However, when clay soils are subjected to severe environmental loads such as elevated temperature variations or penetration of chemicals, the adsorption bonds tend to weaken, which eventually may cause a degeneration of the adsorbed water into bulk water. This degeneration process may affect hydraulic as well as mechanical behavior of saturated clays. In particular, the degeneration of the adsorbed water may critically affect permeability and compressibility of clays. In order to describe this coupled thermal-mechanical-hydraulic behavior, a mixture theory of two interacting clay constituents is developed. Appropriate forms of mass, linear momentum, and energy balance laws as well as constitutive equations are discussed. The focus is on the mass transfer between the adsorbed and bulk water simulating the degeneration of the adsorbed water at elevated temperatures. A cylindrical heating boundary value problem at constant heat output is then discussed and numerical results are presented. A zone of elevated water pressure forms around the heat source, and with time it gradually expands. The permeability may increase locally over 8 times due to the thermal degeneration of the adsorbed water into bulk water. © 1992.

Duke Scholars

Author Tomasz Hueckel Civil and Environmental Engineering