When a clay layer of uniform OCR is subjected to an external load that results in loading of a portion of the clay layer to within the normally consolidated range, there exists a boundary within the clay that separates the over-consolidated material from the normally consolidated material. This boundary changes as consolidation progresses. A finite difference solution based on Terzaghi's one dimensional consolidation theory incorporating this moving boundary between the over-consolidated and normally consolidated states is presented. The coefficient of consolidation, Cv, and the compression indices, Co, are updated to the normally consolidated values when the clay is loaded to the virgin compression range. The solution shows that the rate and magnitude of consolidation settlement varies considerably depending upon the magnitude of load and over-consolidation ratio, although other consolidation properties such as Cv and Cc values being kept unchanged.
In Osaka Bay, Japan, many land reclamation projects are in progress. The most recent and largest is the second expansion of Kansai International Airport. In the Osaka Bay seabed, several slightly overconsolidated clay strata due to the aging effect of consolidation (usually called pseudo over-consolidated clay) exist, such as the stiff Upper Pleistocene clays described by Matsui et al. (1994). When the reclamation fill load is placed on the seabed, many of these Pleistocene clays are loaded beyond the pre-consolidation pressure. Although the compressibilities of the Pleistocene Clays are small in comparison with the superficial soft clay of Holocene period, the magnitude of settlement of these Pleistocene Clays are expected to be significant. This is because the total thickness of the clay layers is significant, as each layer varies in thickness from 15m to 25m. The consolidation settlement of these pseudo over-consolidated clay layers is therefore very important and has to be estimated with a good degree of accuracy.
