Description of Time-Dependent Behavior of Quasi-Overconsolidated Osaka Pleistocene Clays Using Elasto-Viscoplastic Finite Element Analyses

Abstract

The Pleistocene clays in Osaka Bay exhibit slight overconsolidation with OCR of 1.2 to 1.5 in average although they are geologically normally consolidated. Therefore, this seeming overconsolidation is thought not to arise from the mechanical reason but to be subjected to the effect of diagenesis, such as aging effect and/or development of cementation among clay particles. In the sense, the Pleistocene clay deposited in Osaka Bay is so-called “quasi-overconsolidated clays” without definite mechanical overconsolidation history. A new concept is introduced to evaluate the time-dependent behavior of the quasi-overconsolidated Pleistocene clays. In the present study, the stress, p c derived from conventional step loading consolidation test is regarded as the one changing the phase of deformation due to fading the structural effect. Then, the behavior in the region less than p c is assumed no longer elastic but elasto-viscoplastic. The compression curve in terms of e-log p is used but the viscoplastic deformation is assumed to occur even in the region less than p c with the coefficient of deformation, C s . By implementing this concept into elasto-viscoplastic finite element code, the experimental time-dependent compression behavior is found to be well described numerically. Furthermore, the proposed procedure is validated by analyzing the in-situ stress and deformation of one of the reclaimed islands in Osaka Port. The calculated performance can well describe the actual records of settlement for each Pleistocene clay layers monitored by the differential settlement gauges.