# Numerical Simulation Analysis Method for Rockburst Control in Deeply Buried Caverns
## 5 Analysis of the Rockburst Control Effect in Deep Tunnel Excavation
\begin{table}
\begin{tabular}{c c c} \hline
**Elastic Modulus \(E\)** & **Deformation Modulus \(E_{0}\)** & **Bulk Density \(\gamma\)** \\ \hline
15–20 GPa & 8–10 GPa & 2.65–2.7 kN/m\({}^{3}\) \\ \hline compressive strength \(R_{b}\) & friction coefficient f & cohesion C \\
60–70 MPa & 0.95–1.0 & 0.65–0.7 MPa \\ \hline Poisson’s ratio \(\mu\) & Kz = 1.2 & Ky = 1.9 \\ \hline
0.22–0.23 & Kx = 1.5 & Kxy = 0.132 \\ \hline \end{tabular}
\end{table} 
Table 1: The physical parameters of the rock mass. Figure 4: Distribution of rockburst during tunnel excavation. To alleviate the stress concentration in the surrounding rock and actively control rockburst, a total of 28 stress relief holes with a diameter of 50 mm, a depth of 1 m, and a spacing of 1-2 m were drilled in four rows and seven columns on the tunnel face. The borehole arrangement is shown in Figure 4(a). We simulate the effect of the stress relief hole by using the borehole element and evaluate the rockburst control measures after drilling based on the energy theory and strength theory. We can see from the distribution of the rockburst grade that the volume of light, medium, strong, and extremely strong rockburst calculated according to the energy theory is 13.7 m\({}^{3}\), 4.9 m\({}^{3}\), 0.7 m\({}^{3}\), and 0.5 m\({}^{3}\) (see Figure 5(a)), respectively. Compared with the situation without the boreholes (see Figure 3(a)), the distribution of rockburst grade is similar except that (1) the volume of medium rockburst on the tunnel face has decreased by 52.4%, (2) about 33% of medium rockburst has changed into light rockburst, (3) 19.4% of rock mass has avoided rockburst, and (4) the volume of strong rockburst at the bottom corner of the tunnel without the boreholes has not changed. According to the strength theory, the volumes of light, medium, strong, and extremely strong rockburst are 11.7 m\({}^{3}\), 3.7 m\({}^{3}\), 0.8 m\({}^{3}\), and 0.7 m\({}^{3}\), respectively (see Figure 5(b)). Compared with the situation without the boreholes (see Figure 3(b)), the volume of medium rockburst on the tunnel face has decreased by 58.9%, in which about 39.3% of medium rockburst has transformed into light rockburst, 19.6% of rock mass has avoided rockburst, and the volume of extremely strong rockburst remains unchanged throughout the entire bottom corner range of the tunnel without drilling. We can see that the effect of borehole stress relief calculated by energy theory and strength theory on rockburst control is consistent and that the distribution of rockburst grade is similar. The effect of boreholes on rockburst is not strong in both calculations, indicating that the effect of boreholes on controlling rockburst is only partial and that this active control measure is only effective for controlling light rockburst. Figure 5: Boreholes and anchor rod arrangement on the tunnel face. 1 is Class II surrounding rock, 2 is Class III surrounding rock, 3 is spray layer, and 4 is concrete lining. Due to the current excavation stage, 3 and 4 are classified as Class II surrounding rocks like 1. Figure 6: Distribution of rockburst after borehole release. Applying anchor rods is an effective measure to passively improve the stiffness of surrounding rock and control rockburst. When the tunnel excavation was completed, four rows of anchors (\(\Phi\)18 [EMAIL_ADDRESS] \(\times\) 1.5 m, L = 1.5 m) were applied promptly on the tunnel face. Two rows of anchors (\(\Phi\)18 [EMAIL_ADDRESS] \(\times\) 5 m, L = 1.5 m) were applied on the side wall. Six rows of anchors (\(\Phi\)22 [EMAIL_ADDRESS] \(\times\) 2.0 m, L = 3.0 m) were applied on the top arch and the arrangement of the anchor rods is shown in Figure 4(b). After using anchor rod support, according to the energy theory, the volumes of light, medium, strong, and extremely strong rockburst are 2.8 m\({}^{3}\), 0.2 m\({}^{3}\), 0.6 m\({}^{3}\), and 0.5 m\({}^{3}\), respectively (see Figure 6(a)).