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 mechanical characteristics of a slate. This rock has a very definite discontinuous 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 in turn allows a complete stiffness matrix to be calculated. As a second step, taking account of the ultrasonic measurements, the moduli of elasticity were determined from uniaxial and triaxial loading tests. The 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 loading-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 levels are validated by compressibility tests.