Characteristics of discontinuity spacing of Yeongdeok granite

Abstract

Discontinuities are major geological features in the rock mass. They can be distributed evenly, randomly, clustered or in combinations of all these. Discontinuity spacing is one of the important parameters in describing the quality of a complete rock mass. Discontinuity surveys are carried out in the field by examining recovered drill-core to estimate possible distributions for discontinuity geometry parameters of rock masses. Discontinuity spacing and frequency data obtained at a field site in eastern Korea were examined by plotting histograms for the two parameters. The examination clearly showed that discontinuity spacing follows negative exponential distribution. A relationship has been established between mean discontinuity frequency and Rock Quality Designation (RQD) as RQDt =100e^−λt(1+λt), where t refers threshold value, e is a mathematical constant and λ is an average number of discontinuities per meter. This equation enables the utilization of different threshold values of t in addition to the conventional value of 0.10 m. It helps to characterize a rock mass in terms of RQD. Therefore this study showed that the conventional threshold value is not always sensitive to study discontinuity spacing in rock masses.