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The Influence of Geostatic and Hydrostatic Forces on Double-Layer Interactions in Soils¹

ABSTRACT

The effects of geostatic and hydrostatic forces on double-layer interactions are evaluated by considering particle separation to be governed by a balance between repulsive Coulombic forces, van der Waals attraction, fluid-phase pressures, and applied and geostatic loads transferred at zones of double-layer overlap. Equations for interacting Sterntype double layers are solved subject to force balance constraints to calculate equilibrium interparticle spacings at zones of double-layer overlap as a function of soil depth for saturated and unsaturated soils in hydrostatic equilibrium. Reductions in double-layer thicknesses by geostatic loads occur at depths of 1.0 to 0.001 m or less. Matric suctions of < 1.0 m also markedly diminish calculated interparticle separation distances. Decreases in interparticle separation with soil depth become less pronounced as bulk electrolyte concentration and counterion valence increase. Surface charge density variations, within the range found in expansive 2:1 phyllosilicates, have much less effect on interparticle spacing than variations in counterion valence, specific adsorption energy, and concentration.

¹ Contribution from the Dep. of Agronomy, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.

² Assistant Professor and Professor, respectively.

Received for publication January 22, 1982. Accepted for publication October 11, 1982.