Collapse Mechanisms of Low Cohesion Compacted Soils

Abstract

Despite the knowledge of collapse phenomena, there have been many documented cases presented in the literature of compacted fills, earth dams, and road embankments which failed at least partially as a result of wetting-induced collapse. Two aspects of wetting-induced collapse not fully explored for compacted silty-sands are the magnitude of collapse and the fabric alteration after wetting. This paper presents the results of two studies of collapse potential of such soils using Double-Oedometer Tests and Scanning Electron Micrographs (SEM's). In one study, silty-sand soils compacted dry of (less than) optimum water content at 90 percent of Modified Proctor maximum dry density showed appreciable magnitude of collapse upon wetting. In the second study, similarly prepared soils with a lower clay content indicate little to no collapse. The sand component of each soil is similar; however, different sources of silt were used in each study. SEM's showed that the silt of appreciably collapsible soils is more angular. Also, clay binds silt grains together leading to a more open structure. The clay quantity triggers the collapse of these soils more than the removal or reduction of capillary force.