The in-situ determination of rock mass characteristics (test procedure and interpretation of results) must be closely associated with the engineering problem encountered (type of structure, foundation and the methods of calculation being used) and must produce the necessary valid information. The present article gives a descriptive account of the general approach to field investigations of rock masses. Some problems connected with test procedure, equipment used and the processing of the results, taking into account specific features of fissured rock masses, are discussed.
La determination in situ des caracteristiques des massifs rocheux (essais et interpretation des donnees) doit être etroitement liee au problème technique pose (type d'ouvrage, de fondation et methode de calcul utilisee) et doit assurer l'information initiale necessaire et valable. On examine le procede relatif aux essais in situ des massifs rocheux. Quelques problèmes concernant les methodes de realisation des essais, le materiel utilise et l'interpretation des donnees obtenues, compte tenu des particularites des massifs rocheux fissures sont egalement etudies.
Die Bestimmung der Kennwerte von Gebirge in situ (Durchfuehrung der Versuche und Definition der Ergebnisse) muß mit der gestellten Aufgabe (unter Beruecksichtigung von Bauwerkstyp, Gruendung und Berechnungsverfahren) abgestimmt werden, um die erforderliche aussagekraftige Ausgangsinformation zu liefern. Im Beitrag wird die allgemeine Konzeption der Durchfuehrung von Großversuchen im Gebirge behandelt. Es werden auch einige Fragen der Methodik fuer die Durchfuehrung der Versuche, der bei Versuchen eingesetzten Einrichtungen, sowie die Auswertung der ermittelten Ergebnisse, unter Beruecksichtigung von besonderen Eigenschaften des Felskörperverbandes betrachtet.
Development of numerical methods of calculations of rook foundations and the finite elements method in a non-linear statement in Particular enlarges the scope of the problems to be solved but at the same time places heavy demands on the scope and quality of geomechanical characteristics. Aside from traditional studies of shear resistance parameters and deformation modulus of the rock mass a demand was created for determination of strength and deformation properties in tension, compression and triaxial loading, the value and orientation of natural stresses, permeability factor as a function of a stressed state of a rock mass, etc. - In-situ investigations are known as the most valid methods of determination of characteristics of the rook mass. But at the same time high costs and labour content of these efforts demand a proper staging of experiments and maximum data acquisition from in-situ investigations at a limited number of tests.
One of the main principles of in-situ investigations consists in the procedure of experiments closely associated with the solution of the raised engineering problem: with consideration for the type of the foundation, design of the structure, behaviour-of the structure integrally with the foundation and methods of calculation. Thus modulus of deformation may be determined in different ways, e.g. by loading of a plane surface of the foundation (method of plane loading plates), loading of the surface of a cylindrical opening(method of radial plates or pressure chamber), triaxial loading, etc. In each case - different results will be obtained because rook masses as contrasted to the ideal elastic media are deformed differently depending on the type of a stressed state. It is obvious that the first method of determination of deformation modulus is the most suitable for calculations of structure settlements and the second one is suited for calculations of lining of hydropower tunnels and the third one is adequate for calculations of a stress strained state by numerical methods, etc. The same is true to determination of other geo-mechanical characteristics and particularly shear resistance parameters. In this case not only the level of stresses but the pattern of their distribution is of importance which is governed by the mode of application of loads to the block. Shears of blocks with moment and moment less patterns of their loading produce different parameters of shear resistance (Fishman, 1976, 1979). For stability analysis of concrete retaining structures (dams, abutments, etc.) the loads on which create the. moment with respect to the center of gravity of the footing section the first method of shear tests is evidently the most suitable one which will be described below in detail. Thus the methods of in-situ investigations should to a certain extent simulate the conditions of foundation functioning which they are intended for (Fishman, 1976). The second principle of in-situ investigations following from the first one consists in consideration of changes in properties of rock masses which occur during construction and operation of the structure. Unloading of the rock mass during rock excavation, decompaction and disturbances due,to explosions and the following compaction, through loading by the structure, water saturation, grouting, instantaneous \seismic) and, continuous power effects, etc. - these are the factors which as a rule result in drastic changes in properties and conditions of the rock mass compared with the conditions of its natural occurrence.
