2007 Volume 47 Issue 2 Pages 285-301
An investigation was conducted into the bearing capacity characteristics of a structured naturally deposited clay soil by means of a soil-water coupled finite deformation analysis based on unconventional elasto-plastic mechanics. The constitutive equation of the soil skeleton was expressed using the Super/subloading Yield Surface Cam-clay model (SYS Cam-clay model), an elasto-plastic constitutive equation model proposed by the authors to describe the mechanisms (structure, overconsolidation and anisotropy) at work in the skeleton structure. To allow a theoretical consideration of a typical bearing capacity problem, a case was assumed in which vertical displacement was applied through a rigid foundation possessing friction. The main conclusions of the study were:
(1) In a highly structured soil, a peak appears in the load-settlement relation, accompanied by a considerable localization of strain and a clearly visible slip line. In a soil of high initial anisotropy, the area of failure is more confined and the peak load is smaller than in an initially isotropic soil.
(2) In the case of a highly structured soil possessing an initial imperfection, even if this is very slight, a sensitive response occurs, leading to an asymmetrical deformation mode. At the same time, the load-settlement curve “bifurcates” from the path the same soil exhibits when it is deformed symmetrically, so as to display a larger decrease in load.
(3) If loading is relaxed from a rapid rate (≒ completely undrained), at which virtually no migration of pore water can occur in the soil, to a rate that is slower, the peak load will gradually increase with the partial draining effect. If the rate of loading is reduced still further, a point will eventually be reached where no drop in load is observed and it becomes impossible to distinguish clear boundaries for the area of failure. Depending on the rate of loading, it may be possible to see the clear appearance of a compaction band, caused by soil structure decay in the area of strain localization.
These findings aim to show that the inclusion of a concept of soil skeleton structure in an analysis of this sort is not only a very natural step to take, but also an advance of the greatest importance.
