Abstract(s) :

(Anglais) It is now well known that the mechanical behaviour of chalk is directly governed by its water content. The saturation degree induces the “suction” phenomenon and all the consequences of it (a. o. constitutive law and related parameters). Besides the strict mechanical properties (strengths, stiffness…), the seismic properties (seismic velocity of compression and shear waves) are dependent on the saturation degree of the chalk. The relationship between the several properties also depends on the saturating fluid nature (wettability, physico-chemical interactions) and on the chalk structure. This paper aims to present the so far unpublished results obtained in the framework of Master and PhD Theses supported at the Université Libre de Bruxelles and at the Université de Mons. It presents the basic mechanical properties (strength) as well as the experimental studies (methods and results) leading to a new model describing the variation of wave velocity as a function of fluid content. The paper first describes the studied chalks and replaces them in the general framework of the relationships "structure / behaviour". Then the general mechanical behaviour of the tested chalk is recalled, including parameters values and their variations with moisture content. The third part of the paper is devoted to the analysis of the seismic wave velocities as a function of the saturation degree. Previous results are presented in introduction to the new studies. The new experimental results are analyzed and a new model is presented. It consists of a generalization of the Gassmann model, using a theoretical fluid with weighted average water/air. The model defines a critical saturation ratio for each rock which is directly linked to the shape of the rock porosity distribution.