DELAYED COMPRESSION/CONSOLIDATION OF NATURAL CLAY DUE TO DEGRADATION OF SOIL STRUCTURE

The superloading yield surface concept applied to the original Cam-clay model is examined for the application to the one-dimensional consolidation problems of highly structured soils. When the proposed elasto-plastic constitutive model is taken to be the case for a structured soil, the one-dimensional consolidation computation clarifies the following : (1) Delayed consolidation should occur even under one-dimensional compression condition with a considerably low stress ratio when softening of the soil occurs with volume compression. The delayed consolidation is the consolidation process that has sometimes been referred to as "secondary compression". (2) The structure is always degrading as plastic deformation proceeds even within the period of "secondary compression". (3) The decay of overconsolidation to normal consolidation also proceeds with plastic deformation. In this sense, the degradation of structure can not be independent of the decay of overconsolidation. However, since the decay of overconsolidation is much faster than the degradation of structure in clay, then softening becomes possible with volume compression even under a considerably low stress ratio. Recovery of structure with time due to chemical bonding effects etc. in soil particles is beyond the scope of this study.