Rheology is the science dealing with actual (as opposed to ideal) deformation and fracturing behaviour of different materials as a function of stress, temperature, and time. Structure (grain structure and discontinuity surfaces) plays an important role in rock and rock masses. Therefore, the rheology of rock must be termed "structural rheology" or "discontinuity mechanics". The principle features of the theoretical treatment of rheological processes in rock masses result from the analysis of the following: creep, plasticity, and fracturing. These are analysed at different levels: empirical and theoretical investigations of the mechanics of deformation. The influence of temperature (temperature-dependent mechanical behaviour), time (time-dependent mechanical behaviour), and state of stress (non-linear mechanical behaviour) are of primary importance.
La rheologie est une science de la mecanique technique, qui a pour objet le comportement reel, (deformation et rupture), de differents materiaux, en fonction de l'effort, de la temperature et du temps. Dans les roches et les massifs rocheux, l'influence de la structure de la roche (grains et diaclases) est importante. La rheologie des roches doit done être une "rheologie structurale" ou une "mecanique des structures discontinues". Les bases du traitement theorique de la rheologie des roches et massifs rocheux s'obtiennent en analysant les phenomènes suivants: fluage, plasticite, rupture. L'analyse de ces phenomènes se fait à plusieurs niveaux: niveau phenomenologique/empirique, niveau mathematique/theorique, niveau de la rheologie structurale (mecanismes des deformations). Il faut prendre en consideration le comportement mechanique en fonction de la temperature, du temps et de l'etat de contrainte (non linearite).
Rheologie ist ein Wissenschaftszweig der technischen Mechanik, der sich mit dem realen Deformations- und Bruchverhalten verschiedener Materialien in Abhangigkeit von Spannung, Temperatur und Zeit beschaftigt. Im Gestein und Fels spielt der Einfluβ des Gefueges (Korngefuege, Trennflachengefuege) eine besondere Rolle. Rheologie der Gesteine muβ deshalb "Strukturrheologie" bzw. "Diskontinuumsmechanik" sein.
Forty-six papers were presented on topic of the 4th International Congress of Rock !o1echanics,"Rheological Behaviour of Rock- and Rock Masses". In addition, there were three summarizing presentations on special topics. The topics and contents of the papers show that most of the authors perceived the term "Rheological Behaviour" in a broad sense as general "Mechanical Behaviour". On the whole, the problems dealt with, do not differ practically from the papers on general topic 1 "Physical Properties of Rock and Rock Masses" of the Third Rock Mechanical Congress 1974 in Denver. Is rheological behaviour the same as mechanical behaviour? The general report will, therefore, begin with a definition of rheology and will characterize the problem definition and goals of the rheological method of proceeding before the results of rheological research in rock mechanics will be dealt with in detail.
The word rheology is derived from the Greek and means the study of flow. The word is somewhat unfortunate; for even the founder of the rheological science, C.B. BINGHAM, who also coined the word rheology in 1928, understood not only the science of the actual flow of matter (viscous, plastic flow) under the word rheology, but also the science of the deformability of matter in general. It is little known that even many years before BINGHAM, the Swiss hydrologist F.A. FOREL used the word rheology in the "Handbuch der Seenkunde" (1901) and meant, however, the study of the flowing water of the land surfaces.
Rheology as it is presently used, follows the definition of BINGHAM and is thus, a branch of technical mechanics which is separated from the classical mechanics of deformable medias (theory of elasticity, hydrodynamics) as one attempts to come closer to the actual mechanical behaviour of various materials, especially as far as the dependence upon time of the deformation behaviour is concerned.
The main goal of rheology is the establishment of the so-called constitutive laws, which characterize the relationship between forces and the deformation of the matter in dependence upon time and temperature.
In a strict sense, rheological behaviour thus includes time (and temperature) dependent deformation behaviour (creep, plasticity) and in a broader sense, also time dependent fracture behaviour (creep fracture, fatigue).The main emphasis of this state of the art report is the rheological behaviour of rock in the stricter sense, that is, the consideration of creep processes.
During the review of many papers in the field rheology/rock mechanics/engineering geology it is apparent that some central terms of rheology (and of rock mechanics) are, unfortunately, not used uniformly. It, therefore, seems appropriate for better understanding and to ease the discussion, to preceed the following summarizing review with several definitions. Since the original general report on topic 1 is written in German, these definitions are based on the Deutsche Handw8rterbuch der Tektonik (German Hand Dictionary of Tectonics) (1969–1978) and the Deutsche W8rterbuch der Felsmechanik und Ingenieurgeologie (German Dictionary of Rock Mechanics and Engineering Geology) (1975).
