Rock mechanics – Physical and mechanical characterization of rocks: Complete file

2023-05-21 22:00:00

Rock mechanics is a discipline at the interface of mechanics and geology. It belongs to both geosciences and engineering sciences. Its application to engineering problems constitutes a part of geotechnics, in the same way as soil mechanics. If many concepts developed within the framework of soil mechanics are applicable to rock mechanics, the differences between these two geomaterials imply differences in mechanical behavior and therefore the definition of concepts specific to rocks that this article, accompanied by the article [C 352], aims to highlight. When we are interested in the mechanics of rocks, we must distinguish the rock (which we will also call the rock matrix in this article) from the rock mass, the latter being made up of discontinuities in addition to the rock matrix.

In this article, the point of view adopted is that of the application of rock mechanics within the framework of engineering projects, which generally concerns the scale of the rock mass. The writing is therefore oriented bearing in mind the application of the concepts of rock mechanics to the object of study which constitutes the rock mass. Any project concerning the rock mass requires that this rock mass be recognized and precisely characterized from a geotechnical point of view. A rock mass is a discontinuous medium composed of more or less intact blocks of rock, separated by discontinuities of different natures. It is also a heterogeneous, anisotropic and multiphase medium, whose behavior is also affected by a strong scale effect. This article aims to present the essential concepts of rock mechanics and focuses on the properties of the constituent rocks of rock masses. The characterization of the discontinuities and the rock mass is the subject of the article [C 352].

The article is organized as follows. First, a general description of the rocks and the basic concepts necessary to understand their behavior are provided. The following six sections aim to present the main elements of the characterization of these rocks. Thus, the second section is dedicated to the petrographic description of rocks while the third section focuses on the main physical properties of rocks useful for rock mechanics. The fourth section is devoted to the geomechanical characterization of the rocks constituting the rock matrix of the massif. In this section, the main mechanical properties of rocks, in particular deformability and resistance, as well as the failure criteria adapted to rocks, are presented. The main tests used to characterize this mechanical behavior are also discussed. The fifth section presents the basic concepts necessary for understanding the thermo-hydro-mechanical coupling phenomena developing in rocks and which have a strong impact on their response to various stresses. Finally, the sixth section deals with classic rock mechanics tests aimed at determining certain mechanical properties that are decisive in geotechnical engineering projects, with regard, for example, to the choice of digging/drilling methods and tools.

Moreover, for a more global view of rock mechanics and these issues, the reader can refer to the article [C 352] which deals on the one hand with the description and the geomechanical characterization of the discontinuities, structuring the massif into blocks of rock, and of the rock mass resulting from the rock/discontinuities assembly, and on the other hand with examples of application of rock mechanics to geotechnical engineering.

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