Effective forces in saturated clays

Abstract

This paper is the culmination of a five-phase research effort investigating overpressured soil and rock formations. These formations, found all over the world, at varying depths, contain pore water confined at pressures greater than the hydrostatic pressure. Earlier phases developed explanations for this behavior by evaluating the relationship between permeability and porosity that exists offshore due to rapid deposition of soil sediment, and by developing an effective force equation that contains ratios of soil and water contact areas. These studies were useful for predicting overpressured formations, but only at great depths. This study looks at values of grain to grain contact area at low pressures. Modified consolidation tests using a Bishop oedometer were used to apply loads comparable to depths of 35 meters, to three different soil types. Utilizing the oedometer's ability to simulate the pressures within the middle of a soil mass, pore pressure and porosity data were collected and used in a series of power law functions to determine ratios of soil and water contact area. From these tests, the porosity/area of water ratio relationship was accurately determined for each material type. This relationship can now be used to predict locations and magnitudes of overpressured formations.