Estimation of rock discontinuity mean trace length and density from an outcrop in Wenchuan, China

The equations exist in the literature to estimate corrected mean trace length and corrected two dimensional density of a discontinuity set using area sampling technique are critically reviewed. A shortcoming that exists with the equation proposed to calculate the corrected mean trace length of a discontinuity set based on a circular sampling window is pointed out. Also the major shortcomings that exist with the equation proposed to estimate the two-dimensional density of a discontinuity set using a circular window are pointed out. The discontinuity traces appearing in the outcrop in Yingxiu area are used along with rectangular windows to calculate the corrected mean trace length and two-dimensional density using Kulatilake and Wu's equations by incorporating the corrected relative frequency of each trace appearing on the two dimensional exposure. For both the corrected mean trace length and the two-dimensional density, the predictions based on the rectangular window methods are found to be quite accurate.