Determining the anisotropy of rocks has in the past been difficult and rarely attempted in engineering practice. Here we have developed a new practical methodology for measuring orthotropic anisotropy that requires only one hollow cylinder specimen to determine the anisotropy of a set, even when the directions of the anisotropic axes are unknown.

Autrefois, la determination de l'anisotropie des roches etait difficile et elle a ete rarement essayee dans la pratique de l'ingenierie. Voilà c'est nous qui avons mis au point une nouvelle methodologie pratique pour mesurer le coefficient de conductibilite thermique de l'anisotropie qui exige un seul specimen du cylindre creux afin de determiner l'anisotropie d'une serie, même si les directions des axes anisotropiques sont inconnues.

Frueher war die Bestimmung der Anisotropie von Gesteinen ein schwieriges Verfahren, das in der technologischen Praxis nur selten in Angriff genommen wurde. Wir haben hier eine neue praktische Methodik zur Messung der orthotropen Anisotropie entwickelt, bei der nur ein Hohlzylinder an Gesteinsproben benötigt wird, um die Anisotropie einer Reihe von Steinen zu bestimmen, selbst wenn die Richtungen der Anisotropieachsen unbekannt sind.

Introduction

Rocks and earth are anisotropic at every size level from small specimens, tunnels and units of rock mass to the crust. The deformability in one direction can be as much as twice or more of that in the other direction. The cause of the anisotropy of rock is its layered structure or arrayed discontinuities, and hence it can be said to be inherent to rock or soil.

Many previous authors have stated that neglecting anisotropy can result in significant errors (Amadei, 1983). However measuring anisotropy has often been disregarded in engineering practice. This is partly because there are too many parameters to be determined, and partly because the precision is affected by the spatial variations of matter when more than one specimen is used.

Until now 2D analysis has been most prevalent, for example for tunneling, and hence simple 2D evaluation of anisotropy was sufficient. However, recent advances in computer power mean that 3D analysis is now becoming common. This being the case, an exact evaluation of 3D anisotropy is required.

This paper deals with a new method of determining the anisotropy of rocks for use in practical engineering.

Principle of The Method
Test

Many kinds of tests could potentially be used for determining anisotropy of rock, such as the Vp and Vs test on cores from different directions, uniaxial loading test of cores from different directions, and Brazilian tests (Amadei, 1996). Theoretically, anisotropy can be determined by various loading tests or Vp/Vs test on sufficient number of directions.

Difficulty is often encountered however in the actual determination of anisotropy. This is partly because there are too many unknown parameters, and partly because rock properties vary from place to place, whereas many of the tests need more than one specimen to determine a set of anisotropy. The size of the specimen is another problem.

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