The problems of flow and transport in porous media present many fascinating challenges to students of mechanics: and it is surprising that, over the years, these questions have received relatively little attention at the Congresses and Symposia of IUTAM and of its predecessors. The 1964 Grenoble Symposium (Kravtchenko and Sirieys 1966) touched on certain special aspects and the 1966 Vienna Symposia (Parkus and Sedov 1968) had some relevance; but the first specific involvement of the Union with flow in porous media was a useful but limited meeting, sponsored jointly by IUTAM and IUGG, at Calgary in 1971.

Flow in porous media

The generalization to swelling soils of the mathematical theory of water movement in unsaturated soils involves the following extensions to the classic analysis: (1) recognition that Darcy's law applies relative to the soil particles, (2) inclusion of the void ratio function in the characterization of the soil, and (3) reconsideration of hydrostatics in swelling media. For swelling soils the total potential includes an additional component, the overburden potential Ω. Evaluation of Ω leads to the condition for equilibrium in the vertical, which is a first order linear differential equation with singular coefficients. Three types of equilibrium profile follow: hydric profiles with moisture gradient d∂/dz 0. Other phenomena in swelling soils treated include steady vertical flows and unsteady horizontal and vertical flows. Classic concepts of ground-water hydrology, tacitly based on the behavior of nonswelling media, fail completely for swelling soils. The approach also provides a theory of consolidation which includes the influences of (1) soil particle movement, (2) unsaturation, and (3) self-weight.

Hydrostatics and hydrodynamics in swelling soils

Direct observation of surface displacement in two New England salt marshes shows that shrinking and swelling of the sediment is an important mechanism for water storage. This mechanism accounts for 20 per cent of the total change in water content of the sediment in Belle Isle marsh, Massachusetts, and for as much as 36 per cent and 86 per cent of the total at separate sites in Sippewissett Marsh, Massachusetts. Swelling in response to infiltration appears to follow the infiltration model of Hemond et al. (1984). Shrinkage decreases the aeration of the sediment compared to soils that do not shrink, and reduced aeration represents a physiological stress to vegetation. For a given depth of water loss, e.g. one day's evapotranspiration, more shrinkage, less aeration, and higher stresses on vegetation will occur in deeper sediment deposits.

Mechanisms of water storage in salt marsh sediments: The importance of dilation

Theory of infiltration: infiltration into swelling soils in a material coordinate.

Reply [to “Comments on ‘Hydrostatics and Hydrodynamics in Swelling Soils’ by J. R. Philip”]

The paper discusses, with the aid of calculated examples, applications in hydrology and soil mechanics of the analysis developed in Part I Various classical concepts of groundwater hydrology fail completely for swelling soils The distributions of saturation and of hydraulic conductivity relative to the water table differ entirely from the conventional picture Variations in surface topography affect moisture distribution in swelling soils The theory of this effect is developed for topographies that are not too steep and is illustrated by examples The equilibrium distributions found would be classically interpreted as disequilibrium states persisting because of small hydraulic conductivity; but, in fact, the moisture differentials are maintained, not by a lack of conductivity, but by a lack of difference in total potential The variation of specific yield with water table elevation and stratum thickness in swelling soils is basically different from that in non-swelling soils The analysis of Part I is used to discuss the following topics in soil mechanics: the variation of equilibrium soil levels with water-table depth, and with water depth over the soil; the effect of surface loading on equilibrium moisture profiles and on soil levels Extension of the analysis to two- and three-dimensional systems is treated briefly

JR Philip

Papers

Moisture equilibrium in the vertical in swelling soils. II. Applications