CHARACTERIZATION OF THE MODULI OF ELASTICITY OF AN ANISOTROPIC ROCK USING DYNAMIC AND STATIC METHODS

The tests reported in this paper were intended to determine the mechan ical characteristics of a slate. This rock has a very definite discont inuous planar anisotropy superimposed on mineral lineation. As a first step, ultrasonic measurements were carried out to determine the main structural axes. The dynamic moduli of elasticity can be calculated if the velocities of the compressional and shear waves are known. This i n turn allows a complete stiffness matrix to be calculated. As a secon d step, taking account of the ultrasonic measurements, the moduli of e lasticity were determined from uniaxial and triaxial loading tests. Th e confining pressure is shown to have a definite influence on Young's modulus, measured at right-angles to the schistosity. Calculating the shear modulus is a fairly complex operation; clinotropic tests with lo ading-unloading cycles are necessary for an understanding of the large difference in observed values between dynamic and static shear moduli . The laws of evolution of the moduli as a function of confinement lev els are validated by compressibility tests.