ABSTRACT:

The determination of the material parameters of cross-anisotropic rock by laboratory testing is not always possible due to the disintegration of the samples. An alternative possibility is the determination of the parameters from large-scale field experiments, e.g. cavity expansion tests. However an analytical solution for the displacement of the cavity wall in dependence of the applied pressure and the orientation of the schistosity is still missing. A new approximative solution is presented in this paper. The approach assumes linear-elasticity and hydrostatic stress applied upon the wall of a cylindrical cavity. Measurements from cavity expansion tests (radial jack tests) are used to back calculate the material constants.

1 INTRODUCTION

Metamorphic and sedimentary rocks exhibit anisotropy due to the complex mechanical, thermal and chemical processes taking place during their formation. The anisotropy of rocks is of great engineering interest and must be taken into account in planning of many engineering problems especially in dams, tunnels, foundations, radioactive repositories and petroleum engineering problems. Rocks composed of parallel layers (sedimentation or schistosity), e.g. schists, phyllites, shales, etc. belong to the so-called cross-anisotropic or transversely isotropic materials. In this paper the word cross-anisotropic will be used when referring to this kind of rocks. The assessment of the material properties of crossanisotropic rocks requires static or dynamic laboratory tests in samples whose lamination has variable orientations relative to the loading axes (Amadei 1996; Wittke 1984). The methods presented in Talesnick & Rigel (1999) and Gonzaga et al. (2008) can determine the 5 material parameters from only one single specimen. It should be mentioned that most of the existing literature refers to experiments in materials that do not disintegrate by cutting, e.g. diatomite (Boehler&Sawczuk 1977), limestone, sandstone, etc. Field tests were/are also used for the determination of the deformability of anisotropic rock in situ.

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