DISCONTINUITIES AND ROCK MASS GEOMETRY

Variation in discontinuity frequency as a function of scanline orientation in a plane is studied for rock masses containing sets of discontinuities. The spacing values between discontinuity intersection points that can occur along such scanlines are considered in order to develop a probability density distribution of block lengths. The ideas are extended to block area and volume distributions synthesized from the products of discontinuity spacing values along two and three axes respectively. Such distributions are also considered for rock masses were each discontinuity occurs with a random orientation. Histograms of discontinuity spacing and block area values compiled from measurements made on a variety of rock exposure from Pre-Cambrian to Jurassic are in general agreement with the theoretical distributions. The results are presented in dimensionless form and an explanation of the procedure for determining the scaling factors that allow computation of block area and volume distributions for a particular rock mass is included. © 1979.