Volume 3, Issue 7 (July 2006)
Consolidation Yield Stress of Osaka-Bay Pleistocene Clay with Reference to Calcium Carbonate Contents
Sea bottom has been used as landfill sites to dispose various types of waste and dredged materials. Therefore, the geotechnical properties of seabed are of great importance for the design and practice of reclamation projects. Marine clay layers are known to be geologically normally consolidated. Those clays, however, show pseudo-overconsolidation behavior with a consolidation yield stress pc larger than the in situ overburden pressure p0. As consolidation behavior of those clays under a load around pc is not normal but very complex, the prediction of possible settlement under loading is presently quite difficult. In this study, the Osaka-Bay Pleistocene clays were sampled and subjected to physical and mechanical tests. Based on previous studies, it is assumed in this paper that the disagreement between p0 and pc results from the cementation of marine soils, and that their cementation is mainly due to calcium carbonate. If the assumption made is valid, pc value of a clay sample of which calcium carbonates had been chemically dissolved must be equal to p0 value. In order to verify this assumption, experimental studies has been done. Carbonic-acid water of enough volume to dissolve the calcium carbonates in a clay sample was percolated without breaking fabric structure of the clay skeleton, and pc value of the sample was determined by the constant strain rate of consolidation test. The results showed a definite decrease of the pc value. Consequently, the pseudooverconsolidation ratio of the specimens decreased with the removal of calcium carbonates.