ABSTRACT

Petrologic and geochemical factors strongly influence the compaction of clays and sands under pressures between 0 and 100 kg per cm². Particle size is the most pervasive of these, both in its consistently inverse relation to porosity and in its control of the influence exerted by the other factors.

The water content of saturated clays is a complex function of the physico-chemical influences on the sorption of water on clay-mineral surfaces. Water content and specific surface increase in the order kaolinite-illite-montmorillonite. Water content seems to be directly related to exchangeable-cation valence in kaolinite, and is inversely related in montmorillonite. Water content is directly related to the concentration of interstitial electrolytes in most clays; however, it is inversely related in very fine grained clays mixed with dilute Na solutions.

Preferred orientation of clay-mineral particles seems to develop at a very early stage of compaction, at pressures near 1 kg per cm². Its development is enhanced by greater initial water contents, greater amounts of carbonaceous organic matter, and perhaps by lesser concentrations of interstitial electrolytes. A tendency to be compressed into domains or submicroscopic oriented aggregates may be typical of fine-grained clays mixed with concentrated Na solutions or solutions of other cations.

Well sorted sands have greater porosities than poorly sorted sands. Angular sands have greater initial porosities and are more compressible than rounded sands of the same size. Admixtures of platy mica particles increase the porosity, compressibility, and elasticity of sands.