SPECTRAL-BASED PEAK-SHEAR-STRENGTH CRITERION FOR ROCK JOINTS

In general, roughness profiles of rock joints consist of nonstationary and stationary components. At the simplest level, only one parameter is necessary to quantify nonstationary joint roughness. To capture the nonstationary roughness, it is suggested that the average inclination angle I, along with the direction considered for the joint surface, b e used. Most natural rock-joint surface profiles do not belong to the selfsimilar fractal category. However, they may be modeled by self-aff ine fractals. It is shown that even though the fractal dimension D is a useful parameter, it alone is insufficient to quantify the stationar y roughness of non-self-similar profiles. A new strength criterion, wh ich includes three roughness parameters (D, I, and a spectral coeffici ent, K-s), is suggested for modeling the anisotropic peak shear streng th of rock joints at low normal effective stresses. Joint roughness da ta should be used to estimate the roughness parameters in different di rections on the joint surface. Parameter D reflects the rate of change in length of the profile in response to a change in the scale of meas urement r. Parameter K-s may be used to model the scale effect. A vali dation study shows that the new equation has good capability to predic t the anisotropic peak shear strength of joints. In practice, to allow for modeling uncertainties, the new equation should be used with a fa ctor of safety of about 1.5. Comparisons are also shown between the pr edicted shear strengths based on Barton's equation and the measured pe ak shear strengths.