Consolidation of Natural Clays and Laboratory Testing

Abstract

A numerical model has been developed, making use of a strain-rate-dependent compressibility law and a permeability-void ratio law, both experimentally established. The numerical program is used to simulate the behavior of clay specimens submitted to oedometric tests (MSL, CGT, creep, etc.). The following conclusions are drawn: 1. The effective stress-strain clay behavior depends on the type of test carried out. In particular, the preconsolidation pressure value varies from one test to another. 2. Each element throughout the specimen follows a specific stress-strain relation depending on its strain rate history. Moreover, the oedometric curve, as usually interpreted from a multiple-stage loading (MSL) test, does not agree with any of these relations, not even with the average curve followed by the whole specimen. 3. The pore pressure isochrones maintain the same shape during controlled-gradient (CGT) or creep tests, in particular when the effective stresses correspond to the preconsolidation pressure.

An Elasto-Viscoplastic Model for Clay Considering Destructuralization and Consolidation Analysis of Unstable Behavior

“…is the stress ratio tensor (,q = (Sido-0) and M it is the value of re = ,Irgig when the volumetric strain (8) in which ƒÐ'a is assumed to decrease with an increasing viscoplastic strain as (9) where z is an accumulation of the second invariant of the viscoplastic strain rate.…”

“…Bishop and Lovenbury (1969) conducted constant stress creep tests under drained conditions on undisturbed clay, and observed a sudden increase in the strain rate. Kabbaj et al (1985) and Leroueil et al (1985) carried out oedometer creep tests on Champlain sea clays and reported a temporary increase in the settlement rate ( Fig. 1).…”

“…Kabbaj et al (1985) analyzed one-dimensional creep tests by the finitedifference method using an elasto-viscoplastic constitutive model (Oka, 1981), in which different values for the viscoplastic parameters were chosen for the strain level. They showed that the strain rate remains momentarily constant during creep simulations around the preconsoli- Sudden increase in strain rate during oedometer tests on a natural clay Leroueil et al, 1985) 29 dation pressure, whereas the experimental results shows a temporary increase in the strain rate.…”

Modeling the viscoplastic behaviour of clays during consolidation: application to Berthierville clay in both laboratory and field conditions

“…1b presents the normalized effective stress -strain curve for the same clay. Since the work done by Leroueil et al, it has been recognized (Kabbaj et al 1986) that the viscous model previously described should be defined in terms of plastic strain rather than total strain. The implications of the viscous behaviour of clays during one-dimensional compression have been described by Leroueil et al (1985), Leroueil (1996), and Leroueil and Marques (1996).…”

Time-Dependent Deformation Behavior of Jiangsu Marine Clay

“…Therefore, it is necessary to develop a model that takes into account the viscous nature of consolidation of clays (Mitchell, 1993;Leroueil et al, 1985). Taking into account the viscosity during primary consolidation, several constitutive models were developed in the past either as a function of time-dependent characteristics (Yin and Graham, 1989a, b) or as a function of strain rate ( _ e e) (e.g., Kabbaj et al, 1986).…”