An Investigation of Static and Dynamic Data Using Multistage Triaxial Tests
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The focus of this work is to develop an improved understanding of the relationship between static and dynamic data. “Static” data is defined as the large strain (> 10-3) measurements on the unloading and reloading tri-axial stress paths. The “Dynamic” data is the small strain (<10-6) data acquired using standard acoustic velocity measurement techniques. Comparisons are made for both Young’s modulus and Poisson’s ratio along these stress paths. Quadratic fits have been applied to the static data on both the unloading and reloading cycles. This allows us to separate the elastic response into a linear elastic term, M1, and a nonlinear elastic term the “hypermodulus”, M2. M1 is interpreted to be dominated by the stiffness of the grain contacts and follow a Hertzian contact model. It is shown to increase linearly with deviatoric stress and independent of confining stress for both the unloading and reloading cycles. The magnitude of M2 is attributed to the opening and closing of compliant pores and decreases with increasing confining stress. This interpretation for M2 results from the correlations we find between the nonlinear term and the irrecoverable strains. To our knowledge this is the first time the physical mechanisms behind the static and dynamic elastic responses have been isolated.