In the submitted paper, some of the most recent results of rock mass investigations carried out by LNEC are summarized, involving the evaluation of the initial state of stress and the deformability and resistance characteristics of rock masses. Statistical analysis of joint behaviour and scale effects connected to in situ deformability tests are also mentioned. Finally, a proposal of methodology for caverns in rock, mainly based on the use of LNEC test techniques, is expounded by the author.
In dem eingereichten Referat werden einige der juengsten Ergebnisse von Felsuntersuchungen zusammengefasst, die durch das LNEC durchqefuehrt wurden und die Abschatzung des urspruenglichen Spannungszustandes und der verformungs- und Festigkeitseigenschaften von Felsen betreffen. Statistische kluftverhaltensanalysen und mit den In-Situ-verformbarkeitsversuchen verbundene Skaleneffekte werden auch erwahnt. Schliesslich wird eine Untersuchungsmethodologie fuer kavernen in Felsen, die hauptsachlich auf der Benutzung von LNECVersuchsverfahren fusst, vom Verfasser vorgeschlagen und im einzelnen dargestellt.
Des resultats recents de recherches conduites au LNEC sur la deformabilite, la resistance des massifs rocheux et l''etat de contrainte sont presentes dans cet article, en meme temps qu''une methodologie pour l''etude geotechnique des cavernes rocheuses, fondee essentiellement Sur l''emploi des techniques developpees au LNEC est proposee par l''auteur.
Concerning the geotechnical study of rock masses for caverns, a commendable rule should be the testing of every zone of the surrounding rock mass, the mechanical characteristics of which one should expect to have Some kind of influence on the behavior r of the underground structure to be designed.
However, the technological and economical limitations of the in situ and laboratory testing techniques generally prevent a sufficiently detailed mechanical investigation and recommend a criterious employment of the available resources, In order to get the maximum of results with a mini mum of investment.
The heterogeneity and anisotropy of the rock, as well as the scattering of the geo metric and mechanical characteristics of the discontinuities give the rock masses a complex mechanical behaviour, the analysis of which requires the use of simplified models, It should always be borne in mind that mechanical parameters to be determined are strictly connected with morphological and structural characteristics of the rock mass and consequently, with the model of analysis to be used in design.
As far as underground structures are concerned, models reproducing the rock mass as a continuous medium and models al lowing individualized representation of discontinuities have been used. In this case, due to practical reasons, only the Individual. simulation of the most important discontinuities, namely the principal joint sets and faults, is possible, the rock mass between these discontinuities being represented as a continuous, isotropic or anisotropic medium. Therefore, the study of the surrounding rock mass for the design of caverns requires the difinition of the geotechnically relevant discontinuities and their geometrical and mechanical properties, and the definition of the properties of the continuous medium equivalent to the rock mass comprised within these discontinuities. Rock properties, usually determined in the laboratory, constitute the upper most 1imit of such medium.
The definition of the mechanical behaviour of this equivalent continuous medium has to be made by means of in situ tests, on representative samples of the rock mass, that is, on volumes which, owing to their size, include rock and discontinuities in such proportions as to reproduce the mutual mean influence of these two components in the test zone. As to the mechanical cha racterization of the discontinuities, it may be carried out, mainly by means of laboratory and in situ shear tests, which, at though similar, differ in the size of the test samples and, therefore, in the representativeness of their results.