Généralités sur les propriétés mécaniques des sols. Nouveaux appareils de mesures. Petites digues sur vases

General considarations on mechanical soil prperties. New measuring instruments. Dyke construction on mud foundations

Professeur à la Faculté des Sciences de Grenoble.

Résumé

Plastic flow laws express relationships between stress and strain space paths, the latter being identified in tenns of lime. A distinction can be made between continuous strain and dis conti nuity surface laws. To establish these, it is necessary to carry out tests in order to measure stress and shain tensors, which can only be done with a homogeneous spatial tensor distribution. As the instruments do not produce homogeneous fields, they can only measure the parameters of a law if the law is known. In theory, plastic flow laws can be established with the aid of general relationships between particles and from the geometry of the structure. A material for which these relationships are constant only changes its mechanical properties with the geometry of its structure, which solely depends on irreversible strains undergone by the material; this explains the "work-hardening' or "super-consolidation' which, with a sufficiently simple path, can be characlerized by the stress tensor for the final irreversible strain. The author introduces a new laboratory instrument for the measurement of the plastic flow relationship for very high homogeneous strain conditions, and also a simple instrument for quick in situ cohesion, friction and stability measurement, especially for sand and mud. Muel can be considered as not very dense normally consolidated soil having remained under water since its original deposition. The author has no precise measured plastic flow data available for mud; he simply correlates its physical and mechanical properties. For example, as its water content is near the liquidity limit WL at shallow depUIS, its approximate compressibility can be established from WL. The relevant cohesion data show considerable scatter but the average values for individual sites appear to increase with the consistency index. Rapid construction on mud results in high interstitial pressures, i.e. very low strength if the mud contains little clay. Bearing strength can be much improved by the use of non-stretch matting placed crosswise, for which the author suggests a calculation method.