Spatial distribution of stochastic discontinuities of Shazaoyuan granite masses in Beishan

Shazaoyuan granite masses is an alternative site for high-level radioactive waste disposal in China. Taking the outcrop joints and borehole fractures in 600m3 Shazaoyuan granite body as the object, the spatial distribution of stochastic discontinuities in rock mass was explored. According to occurrence statistics and cluster analysis, the rock mass mainly develops stochastic discontinuities with dip angle greater than 65 °and strike of NNE, EW and NW. The dominant sets of fractures are 295.4°∠ 68.3°, 189.5°∠ 71.2°, 235.6°∠ 69.2° and 66.0°∠ 33.0°, and the dominant sets of joints are 320°∠ 79°, 180°∠ 77°, 282°∠ 80° and 231°∠ 67°, showing similar characteristics. The Voronoi was used to divide the surface rock mass, filled by the average trace length and midpoint plane density of complete outcrop joints and split outcrop joints. The average trace length in the northeast of the rock mass is about half of that in the southwest, and the midpoint plane density is the largest in the middle of the rock mass. Compared with other dominant sets, the average trace length of NE and NNE discontinuities is longer, and the midpoint plane density is larger; Based on the division of dominant sets of borehole fractures, the strike and dip angle of different dominant sets in the fractures was presented in depth. The borehole fractures are characterized by uneven depth distribution. The average linear density is 0.11/m, reaching the maximum of 0.60/m in the [-150, -160 m] interval, and NNE fractures are densely developed in the [- 310 m, - 370 m] interval.