Abstract： Large number of joints exist in rocks. Their sizes and directions are distributed in a random way. Studies have shown that the distribution of joints can be quantitatively described by using the fractal dimensions. Based on two rupture modes，fracture propagation and shearing slide，the statistical strength of jointed rocks is derived with the help of the statistical fracture mechanics. The result shows that the strength of jointed rocks strongly depends on the fractal dimension of rock joints. The small increase of fractal dimension will lead to rapid decrease of rock strength.
