The report gives a descriptive account of field plate-bearing tests of a jointed rock mass and their numerical modelling. Scale effects have been studied. It has been demonstrated that in most real cases modulus of deformation of a rock mass rises up with an increase of sizes of a load plate.
Le rapport presente les resultats des essais d"un, massif fragmente a l"etape et de leur simulation numerique. L"effet d"echelle a ete etudie. Il est demontre que dans la plupart des cas reels le module de deformation d"un massif s"accroît avec l"augmentation des dimensions de l"etampe.
Im Beitrag werden die Ergebnisse der Druckplattenversuche im Kluftkörpermassiv und deren numerische Modellierung behandelt. Es wird die Maßstabwirkung untersucht und festfestellt, dass in den meisten tatsachlichen Fallen der Deformationsmodul des Massivs mit der Vergrösserung der Druckplattenabmessungen ansteigt.
The study of a scale factor has a dominant role in evaluation of mechanical properties of rock masses. In spite of relative large number of studies (laboratory, for the most part) until now there is no unambiguous interpretation of the scale effect on the properties of a rock mass. Basically it may be explained by contradiction of the obtained results even for such a simple characteristic as modulus of deformation.
For instance, studies of soft soils (sand and loam) demonstrated that during load plate tests the modulus of deformation rises with an increase of sizes of a plate but sometimes at further increase of the plate size the modulus of deformation decreases. Studies of block models simulating the rock mass carried out by Grishin (1972) showed a decrease of the modulus of deformation with an increase of the plate size but studies pursued by Ukhov (1975) and Rosa & Zelensky (1967) on similar models revealed a rise in the modulus of deformation. In laboratory model tests carried out in the Department of Rock Foundations, Hydroproject (Gasiev, 1977) the modulus, of deformation first decreases with a rise of the plate width but then (beginning from the width of the plate exceeding the rock block size by a factor of two-three) the modulus of deformation rises.
Geophysical investigations pursued by Sa-vitch & Kujundjich (1990) and Ukhov (1975) demonstrated a decrease in the modulus of deformation of the rock mass in the whole range of scale variation within the limits of which elastic wave velocity was measured. On the other hand moduli of deformation obtained by back analysis on the basis of settlement of dams very often appear larger than those obtained by in-situ load plate tests.
The above-mentioned laboratory studies were carried out with different boundary conditions and these studies simulated deficiently the natural rock mass. Geophysical tests were performed in-situ but without loading of the rock mass. The purpose of this work consists in direct studies of the scale effect during in-situ load plate tests and evaluation of main acting factors by numerical modelling of such tests.
In-situ tests were carried out on limestones forming the foundation.
