In order to obtain damage risk indexes of each zone and judge whether the failure occurs, the function get_W, whose solving procedure is displayed in Figure 2, was programmed by using Fish language in [FLAC.sub.2D], based on Mohr-Coulomb strength criterion and the definition of damage risk index.
Under this condition, distributions of damage risk indexes and damaged zones can be obtained after calling the function get_W.
Thus the goal of comprehensively and quantitatively evaluating damage risks can be achieved by defining the damage risk indexes and grades, compared with conventional analysis indexes.
[W.sub.2]-[W.sub.5] indicate the medians of intervals of damage risk indexes at each risk grade from high to no damage risk states; namely, [W.sub.2] = 87.5%, [W.sub.3] = 62.5%, [W.sub.4] = 37.5%, and [W.sub.5] = 12.5%.
The time-history response curves of damage risk indexes of surrounding rocks are revealed in Figure 11, where the straight lines in red, yellow, and blue represent the high, medium, and low damage risks, respectively.
The dynamic response curves of the 1st monitoring points in each position of surrounding rocks are incomplete since they have already been damaged when their damage risk indexes reach 100%.
Due to nonexisting dynamic response peaks on the time-history response curves of damage risk indexes in the floor, the comparison of the dynamic influence indexes regarding damage risks of each monitoring point only needs to be made in the roof and the two sidewalls, as shown in Figure 12.
