Constitutive Relations for Partially Saturated Soils Containing Gas Inclusions

This paper is concerned with a mathematical description of the undrained response of partially saturated soils having a continuous liquid phase (water) and a gas in the form of discrete bubbles. Two types of soil structures are considered. First is the case in which the gas inclusions, of size much smaller than the average particle size, are entrapped in the water phase. Second is the case in which the comparatively larger gas bubbles are embedded in the saturated soil skeleton. The fluid phases are assumed to be separated by boundaries across which discontinuities in pressure exist due to surface tension. The soil is treated as a three-phase composite medium and the mechanical properties are described in terms of average stressstrain measures in all constituents. The mathematical formulation incorporates the average porebubble size as an independent material parameter governing the mechanical response.