fluidsaturated

Fluid-saturated, often written as fluid-saturated or fluidsaturated, describes a condition in which the pore spaces of a porous material are completely filled with a single fluid. In this state, there are no air or other immiscible phases in the pores. The degree of saturation S is defined as the volume of fluid in the pores divided by the total pore volume; for a fluid-saturated material, S = 1.

In many contexts, especially soils and porous rocks, the pore fluid is water, though other liquids or hydrocarbons can occupy the pores. Fully saturated materials exhibit properties governed by the pore fluid, including pore pressure, hydraulic conductivity, and the mechanical response of the solid matrix through effective stress. In saturated soils, the effective stress is given by the difference between total stress and pore-fluid pressure, σ' = σ − u. When a single fluid fully occupies the pores, Darcy’s law describes steady, laminar flow, with permeability depending on the medium and the fluid’s viscosity and density. If multiple fluids can occupy the pore space, or if saturation changes during flow, concepts such as relative permeability and capillary pressure become relevant, even though the pore space is momentarily fully occupied by one phase at times.

Measurement and testing of fluid-saturated materials involve saturating procedures to achieve full pore filling, porosity assessments, gravimetric methods, and non-destructive techniques such as X-ray computed tomography or neutron porosity methods.

Applications span groundwater hydrology, soil mechanics, petroleum reservoir engineering, and materials science, where the presence or absence of pore fluid significantly influences transport, strength, and acoustic properties.