F. Tavenas

Consolidation of Natural Clays and Laboratory Testing

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 ofclay 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.

DIFFICULTIES IN THE USE OF RELATIVE DENSITY AS A SOIL PARAMETER

THE RESULTS OF A COMPARATIVE TEST PROGRAM REPORTED BY TAVENAS ET AL AT THIS SYMPOSIUM HAVE SHOWN THAT THE RELATIVE DENSITY DETERMINATION IS HIGHLY VARIABLE AND NONREPRODUCIBLE.IN THIS PAPER,THE CONSEQUENCES OF THIS FACT ARE DRAWN. BECAUSE OF THE HIGH VARIABILITY OF RELATIVE DENSITY MEASUREMENTS,THE COMPARISON OF THE PROPERTIES OF DIFFERENT SOILS AS INVESTIGATED BY DIFFERENT ENGINEERS WILL BE IMPOSSIBLE.FOR THE SAME REASON AN ENGINEER CANNOT MAKE AN EFFICIENT USE OF ANY PUBLISHED CORRELATION BETWEEN THE RELATIVE DENSITY AND THE MECHANICAL PROPERTIES OF SANDS SINCE HE WILL NOT BE ABLE TO REPRODUCE THE SAME RELATIVE DENSITY.FINALLY,THE RELATIVE DENSITY CAN BE USED AS A COMPACTION CRITERION ONLY IF THE SAME ENGINEER WHO HAS WRITTEN THE SPECIFICATION IS ALSO IN CHARGE OF THE COMPACTION CONTROL. /AUTHOR/

Some Aspects of Clay Behavior and Their Consequences on Modeling Techniques

Numerical models, as they are applied presently in geotechnical engineering, present serious weaknesses. Basic features of natural soils behavior are presented, and the differences with the common assumptions in constitutive models are pointed out. Some guidelines for the proper use of models and numerical analyses are given.

Les argiles de l'est du Canada et leur contribution à la compréhension du comportement de l'argile

This paper offers a brief and incomplete retrospective of the last 25 years of research on clays in Canada, and especially on the sensitive clays. The implication of this research on the improvement of our knowledge of the behaviour of clays in general is emphasized. The development of special techniques for the study of sensitive clays, such as sampling, and the application of limit and critical states concepts to natural clays have contributed greatly to the important leap forward in our understanding of the soil masses and in the solution of practical problems: the problems of stability, of compressibility, and of consolidation are discussed. Finally, the prominent role of the Canadian Geotechnical Journal in the diffusion and even in the orientation of research in Canada is emphasized. Key words: research, clays, sensitive clays, limit state, critical state, brittleness, sampling, strength, stability, consolidation.