Abstract: Spacing of discontinuities formed in the same tectonic stage is believed to obey a negative exponential distribution. Single factor clustering method according to orientation is most commonly used. However, the probability density function of spacing in one set of discontinuities clustered only based on orientation may be irregular, even exhibiting no rules. To overcome the deficiency, this study proposeds a new double-factor clustering method(NDCM), considering spacing distribution and orientation of discontinuities during clustering. The initial clustering result and membership values are obtained based on the fuzzy K-means. Through redistribution of the discontinuities whose membership values are low, this method adjusts the probability density function of spacing to make it more closely obey a negative exponential distribution. To obtain the clustering precision of NDCM, a numerical model calculation which contained two and three discontinuity sets has been made and the correct set code of every discontinuity were known. The model has been calculated by the two methods. Comparison results show that NDCM has an obvious advantage over fuzzy K means in clustering precision. About 6% promotion occurs in precision clustered by NDCM compared with fuzzy K means.

Key words: discontinuity, clustering, spacing, orientation