Abstract
Stability of rock mass structures and flow of ground water through rock masses are influenced by discontinuities included in the rock masses rather than the rock materials. This paper describes a method of estimating the distribution of rock mass discontinuities, especially the orientation and frequency of sets of discontinuities.
The frequency of discontinuities, λs, defined as the number of discontinuities intersected by a scanline of unit length, depends on the direction of the scanline. When a λs-θ curve is drawn as the variation of λs in rotating a scanline with direction of θ, the orientation and frequency of sets of discontinuities can be found according to the downward cusps appearing in the λs-θ curve. On the contrary, in the RQD-θ curve which shows the variation of RQD values in rotating a scanline or drilling line, upward cusps give the orientation of sets of discontinuities. The ‘cusp’ method is also applied to anisotropy of elastic wave velocity in rock masses, because the slowness of elastic wave passing through rock mass discontinuities is proportional to the frequency of discontinuities. The validity of this method is checked by using data obtained by HUDSON and PRIEST, ODA et al., and so on.
