## 6 Conclusions  
In this paper, the variation of the initial damage variable was firstly determined based on the change in the stress wave velocity in the intact rock under different equal biaxial static loads in the model test, and the Mohr-Coulomb elasto-plastic constitutive model of the rock considering initial damage was established by combining the Mohr-Coulomb strength criterion. The developed rock constitutive model was then numerically implemented using the Fish language in discrete element software UDEC, and the model tests were numerically reproduced in conjunction with the BB model characterizing the nonlinear deformation properties of the joints. Finally, further numerical studies on the effects of the biaxial static load, the angle, and the number of joints on the propagation of stress waves in the jointed rock mass were carried out, and the following conclusions were drawn. 1. The numerical and experimental results of the propagation law of stress waves in the jointed rock masses under different biaxial static loads were compared and analyzed from the perspectives of the waveform, amplitude, and the transmission coefficient of  
Figure 14: Transmission coefficient of the rock mass containing different numbers of 90\({}^{\circ}\) and 60\({}^{\circ}\) joints under biaxial static loads: (**a**) 90\({}^{\circ}\) jointed rock mass; (**b**) 60\({}^{\circ}\) jointed rock mass. stress waves, which were relatively consistent, verifying the feasible of the adopted numerical calculation method. 2. The initial damage variation in the intact rock with the biaxial static load increased first and then decreased. When the biaxial static load was 1.23 MPa, which was about 15.7% of the biaxial compressive strength of the intact rock, the stress wave velocity reached its maximum value while the initial damage was the smallest, indicating that the internal microcracks in the intact rock were in a fully compacted state under this static load. 3. As the biaxial static loads increased, the measured and numerical transmission coefficients of the rock masses containing different angles and numbers of joints all showed a trend of first increasing and then decreasing, and the transmission coefficient was the largest when the static load was about 2.2 MPa, which was about 28.1% of the biaxial compressive strength of the intact rock. 4. The transmission coefficient increased and then decreased with the increase in the joint angle without the static load and was the largest when the joint angle was close to 30\({}^{\circ}\). The transmission coefficient continuously increased with the increase in the joint angle when the static load was relatively small, such as 0.75 MPa and 1.5 MPa, i.e., less than 20% of the biaxial compressive strength of the intact rock. The transmission coefficient decreased and then increased with the increase in the joint angle when the static load was greater than 2.25 MPa (28.7% biaxial compressive strength of the intact rock) and was the smallest at the joint angle of about 40\({}^{\circ}\). 5. Under the same static loading, the transmission coefficients of the jointed rock masses all showed a tendency to decrease with the increase in the number of joints, and the decreasing increment gradually became smaller. The larger the static load, the smaller the decrease in the transmission coefficients caused by the increase in the number of joints, indicating the effect of the number of joints on the transmission coefficients which decreased as the static load increased. 6. In the blasting excavation of the underground rock mass, the in situ stress and the spatial distribution of the joints significantly affected the propagation of the blasting stress wave. When the blasting stress wave vertically impacted the initial stressed rock mass, the transmission coefficient was the largest.