SCALE EFFECTS IN THE STRENGTH AND DEFORMABILITY OF ROCKS AND ROCK JOINTS . PROCEEDINGS OF THE FIRST INTERNATIONAL WORKSHOP ON SCALE EFFECTS IN ROCK MASSES, LOEN, NORWAY, JUNE 7-8 1990

Rock materials and joints tested at different scales often reveal trends of decreasing strength with increasing size of sample. Opinions on the causes of the observed scale effect are divergent. Some argue that the decreasing strength-size relationships of intact rock are introduced by stress-gradients due to non-uniform loading and sample shape influences. Others interpret the strength reductions on the basis of the Weibull statistical volume effect, stored strain energy, etc. However, it appears that no single or combined interpretation explains fully the behaviour. Regarding the shear strength of joints, the consensus is that a scale effect exists, in the broad sense that laboratory measurements cannot be directly applied to in-situ non-planar joints. Practical suggestions include the use of laboratory-measured values of the residual friction angle or the ultimate friction angle plus the inclination angle (i) of large scale undulations. An alternative proposal is the use of a scale-corrected roughness component (in addition to the residual friction angle plus a dilation component, i). (TRRL)