Recent developments make it possible to determine rock mass parameters in close jointed rock masses by means of large scale triaxial tests in the laboratory. A sampling technique for large specimens was developed alternatively to expensive triaxial tests in situ. The sampling equipment and technique as well as the testing machine and procedure are described in detail. The boundary conditions of the tests are given. The results for a mixed layer of sandstone and claystone and for a yellow limestone are presented. The comparison to small-scale tests shows in this case that the rock substance parameters cannot be used to calculate a rock construction because there is no constant relation between both types of parameter.
Des developpements recents rendent possible la determination en laboratoire des paramètres d'un massif rocheux à l'aide d'essais triaxiaux à grande echelle. On a developpe, comme technique alternative à des essais in situ coûteux et necessitant une importante mise en oeuvre. une technique de carottage permettant d'obtenir des echantillons non remanies de grandes dimensions. On detaille l'equipement et la technique employee pour le carottage ainsi que les appareils d'essais de laboratoire et le deroulement de ceux-ci. On indique les limites du procede. On donne comme exemple les resultats d'essais sur un materiau constitue de couches interstratifies de grès et d'argile compacte ainsi que sur du calcaire jaune. La comparaison avec des essais de petites dimensions montre que les paramètres de la roche ne peuvent pas être employes pour le dimensionnement d'ouvrages en roche dans ce cas precis. Une estimation des paramètres valables pour l'ensemble du massif rocheux avec des essais de petites dimensions est peu sûre car le rapport entre les paramètres de la roche elle-même n'est pas constante.
Neuere Entwicklungen ermöglichen die Bestimmung von Gebirgsparametern mittels groβmaβstablicher Triaxialversuche im Labor. Als Alternative zu aufwendigen Triaxialversuchen in situ wurde eine Entnahmetechnik fuer ungestörte Groβproben entwickelt. Die Entnahme von Groβproben. sowie die Versuchseinrichtungen im Labor und die Versuchsdurchfuehrung, werden ausfuehrlich erlautert. Die Versuchsrandbedingungen werden aufgezeigt. Exemplarisch werden die Ergebnisse von Versuchen an einer Wechsellagerung von Sandstein und Tonstein und an einem Kalkstein gegeben. Der Vergleich mit kleinmaβstablichen Triaxialversuchen zeigt, daB die Gesteinsparameter allein fuer eine Bemessung von Felsbauwerken nicht angewendet werden Können, da deren Relation zu den korrespondierenden Gebirgsparametern nicht konstant ist.
The increasing application of modern material laws and calculation methods in rock mechanic problems of underground openings, foundations in rock masses and slopes needs the determination of the stress-strain behaviour of the rock masses more than empirical or half-empirical methods. A great part of the deficit of reliable parameters is caused by incomplete or not existing testing methods. Normally the rock mass parameters are estimated by reduction of the rock substance parameters. This procedure contains the risk that these parameters are either underestimated which causes an uneconomical construction or overestimated which causes sometimes a collaps. Therefore research activities in testing rock mass behaviour are necessary (Mueller et. al., 1977). The report treats new developments for triaxial tests of narrowly jointed rock samples with dimensions up to 0,6 m × 0,6 m × 1,2 m. The relevant range of applications and technical demands for the tests are shown. The derivated basic research, financed by the Deutsche Forschungsgemeinschaft, treats a careful sampling of specimens orientated to the joint systems (prismatic and cylindric samples, boring with prestressing, etc) as well as technical conditions of the triaxial cell for testing under defined stress-strain paths (compression and extension tests, multi-step tests under different confining pressure with regard (or not) to the middle principal stress, time dependence of the material behaviour, influence of water pressure in pores respectively in joints).
The determination of the rock mass parameters is possible in two different types of investigations. One type is the analytical or numerical procedure (John 1969), (Muehlhaus, Reik, 1978). The rock mass behaviour is calculated on the basis of the rock substance and the joint parameters. This method is not useful if the degree of separation is unknown or the joint orientation is nearly normal or parallel to the principal stresses, especially in close jointed rock masses. The other type is the global determination of the parameters at a jointed specimen as a composite - material. This type of investigation includes all effects like those of the rock substance, joints, stratification, degree of separation etc. Therefore it is necessary to test specimens with a representative size. From sufficient fundamental test series in our institute and elsewhere we know that the parameters of the test specimen are relevant to the considered homogeneous area of rock masses, when 5 to 10 joint planes cut the smallest one way dimension of the test specimen. The limitation of this technology is given by the joint distances.
