Much of the research on fracture of rocks or rock-like materials conducted over the past two decades may be considered as "academic studies" of the general phenomenon of fracture. Yet, the understanding of this phenomenon is fundamental if a material is used in any engineering design, whether the aim is to prevent failure of the structure or to promote it. Fracture theories existing are generally empirical and derived from experimental results of laboratory test with simple boundary conditions. Because of the basic weakness of rock intension and because in general the environmental stresses in rock mechanics are compressive most of these theories consider fracture under compressive stress conditions. The Coulomb-Navier-, the Mohr-, the Griffith and the McClintock and Walsh criteria are typical examples and will be considered in the following. In addition the tendency during the past was in making accurate experiments under conditions of homogeneous stresses. To obtain information about the fracture behaviour with unequal principal stresses systems have to be used which involve inhomogeneous stresses. This case is of particular interest, since in practical rock mechanics we may expect conditions of highly inhomogeneous stresses. However, a consideration of such situations involve additional assumptions like the applicability of the theory of elasticity for calculating the stress field, which may be open to question. A distinction has to be made between fracture initiation and fracture propagation, since a detailed observation of the total fracture process in rock was possible by means of "stiff" and "servo-controlled" loading systems.

An important objective of the civil and mining engineer concerned with structures in rock such as tunnels, open pits, dam foundations and so forth is the creation of a safe and efficient design. This necessitates an estimate of the immediate and long-term performance of the surface or subsurface opening or foundation, whichever the case may be. This in turn requires a quantitative estimate of those physical and mechanical properties of the rock mass which govern its strength, permeability and deformation charac- teristics. To a lesser or greater extent, depending upon the type of engineer- ing structure considered, these properties are a function of the 1) attitude, 2) geometry and 3) spatial distribution of the joints and other discontinuities in the mass. All three factors can be determined, since the joints are detect- able features whose characteristics can be quantitatively measured and described. Joints are universally present in rock masses and have strength, per- meability and deformational characteristics appreciably different from those of the intact rock. Depending upon the origin of the joints sets, their characteristics can vary greatly. Not only can the average spacing between joints vary within wide limits, but the nature and degree of joint infilling material, physical characteristics of their planes and their degree of develop- ment can be vastly different. Because of variations in these properties one joint set can have very different effects than another on, for example, shear characteristics. Hence, each joint set should be examined individually for its properties.

Bei der Durchfiihrung der Bauarbeiten fiir den Ausbruch des Hauptstrangs 2 der Zuleitungen Ost des Pumpspeicherwerks Hongrin-Uman ,3 ergaben sich in ihrem AusmaJ3 nicht vorhergesehene Schwierigkeiten. Dieser Stollen miindet prak- tisch am Ende des Staues (hochster Stauspiegel 1255,00 m) auf Kote 1250,00 m, im Tal des Hongrinbaches Paquier-Clavel in das Speicherbecken. Es handelt sich urn 2 einen Freispiegelstollen iiblicher Form, Querschnitt 5 bis 8 m , Langsgefalle 3 %0. Aus der Gesamtanordnung des Stollensystems ergab sich die Notwendigkeit, den Hauptstrang durch das Massif des Mont d'Or zu fiihren (Abb. 1 und 2). Der ,N BASSIN O*"CCUMUlAlION HONGRIN /~ Fain. ,00 0 500 1000" ~ .,f "'j';';;!;iil!~!I~I!;lilt~~:/:~ ?::::::::: :*"'~~~A" Abb. 1. Chaine du Mont-d'Or - Lageplan der Zuleitungen Ost (nach J. Nor be r t, Geologe, Lausanne) Dichter Fels: 1 Tonschiefer mit Kalksandstein; 2 Anhydrit und Gips. Durchlassiger Fels: 3 zermalmte Rauhwacke; 4 stark zerkliifteter Dolomit und Dolomitenkalk; 5 zerkliifteter Kalkstein Chaine du Mont d'Or - Plan of galleries, East adduction Non water-bearing rock: 1 Clayey schist with sandy-limestone; 2 Anhydrite and gypsum. Water-bearing rock: 3 "Cornieules" (crushed yellow honeycomb dolomite); 4 Dolomitic limestone and badly fractured dolomite; 5 Fissured limestone Chaine du Mont d'Or - Situation des adductions Est Roches etanches: 1 Schiste argileux it niveaux greso-calcaires (flysch); 2 Anhydrite et gypse.

Auf Anregung einiger jiingerer Kollegen fand im AnschluB an das Ludwig- Foppl-Kolloquium der Osterreichischen Gesellschaft fUr Geomechanik am 28. Okto- ber 1967 in Salzburg eine Aussprache iiber rheologische Probleme der Geomechanik statt, welche von der Abteilung Felsmechanik am Institut fUr Bodenmechanik und Felsmechanik der Universitat Karlsruhe gemeinsam mit der Osterreichischen Gesell- schaft fUr Geomechanik veranstaltet wurde. An die einleitenden Vortrage schloB sich eine lebendige Wechselrede an, welche so viele und interessante Kontakte zwischen den von den einzelnen Teilnehmern vertretenen Arbeitsgebieten anspringen lieB, daB es den Herausgebern wert er- schien, die ganze Aussprache, zwar in konzentrierter Form, im wesentlichen aber doch vollstandig, wiederzugeben. Fiir die umsichtige Mitarbeit bei der Vorbereitung und DurchfUhrung des Kol- loquiums sowie bei der Redigierung der Diskussionsbeitrage gebiihrt Herrn Dipl. -Ing. H 0 fm ann, Karlsruhe, besonderer Dank. Leopold M ii 11 e r-Salzburg Inhaltsverzeichnis Einleitende Vortriige Leipholz, H. : Grundlagen der Rheologie ...Langer, M. : Grundbegriffe der Rheologie und ihre Anwendbarkeit bei der Verformung von Gebirgskorpern ...9 Zisminsky, U. : Rheologie und Felsmechanik aus geologischer Sicht ...2L Korner, H. : Kinematische Betrachtungen zum Rankineschen Spannungszustand in der geneigten, kriechenden Schicht ...33 AU88prache 1. Begriffe 55 Elastisch - plastisch - viskos - FlieBen - Kriemen II. Kin e mat i s c h e K r i e c h the 0 r i e ...64 Frage der Standsimerheit - Probleme des Stoffgesetzes und der Bruchbedingungen III. Probleme des GroBenbereiches ...70 Kontinuum - Diskontinuum - Bestimmung von Gesteins- und Gebirgsparametern Felsmechanik u. Ingenieurgeol. , Suppl. V.