## 2 Stress Release and Energy Dissipation Mechanisms of TBM Tunnel ASRBs  
As the TBM tunnel face advances, based on elastic-plastic mechanics theory and the distance from the surrounding rock, the excavation damage zone (EDZ) and the original rock stress zone is formed in the surrounding rock [37], where the maximum principal stress concentration area is located at the junction of the EDZ and the original rock stress zone, as shown in Figure 1a. Near the TBM cutter head, the maximum principal stress concentration is close to the side wall, and the hard rock mass in this area has accumulated a large amount of elastic strain energy under the action of high ground stress [38], thus forming a potential rockburst source area, threatening the safety of engineering equipment and construction personnel. To ensure the smooth progress of TBM tunneling and to prevent geologic hazards such as jamming or rockbursts, it is necessary to release the energy in the rock around the TBM cutter in advance. For this reason, in the limited space behind the cutter head, the high stress and elastic strain energy in the maximum principal stress concentration area can be released in advance by reasonably applying ASRBs and using their stress release and energy dissipation effects, as shown in Figure 1b, to effectively reduce the possibility of a rockburst in the surrounding rock during TBM tunneling. In tunnels constructed by the drilling and blasting method, SRBs are often constructed in the side wall, top arch, and face of the tunnel, depending on the different target areas for stress release, as shown in Table 2. Research in the field of coal mining has found that reasonable placing of SRBs in high-stress roadways can improve the stress environment of the surrounding rocks in the following two ways: (1) SRBs release energy accumulated in the surrounding rock masses, transfer the stress concentration area to deep areas, and reduce the stress concentration degree [39]; and (2) the drilling process can lead to structural pre-splitting failure of the roadway-surrounding rock, thus reducing its brittleness and ability to store elastic strain energy [40]. Figure 1: Cont. To obtain a simple simulation process for the unloading mechanism of the stress release borehole in general, FLAC\({}^{\text{3D}}\) 6.0 finite difference software [43] was used, and the simulation results under different SRB deployment scenarios are shown in Figure 2. In this case, granite \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Layout Location** & **Schematic Diagram of the Drilling Design Scheme** & **Applied Tunnel Engineering** & **References** & **The Specific Layout of the SRBs** \\ \hline \hline \multirow{4}{*}{Tunnel side wall} & & & SRBs are staggered in the side wall of the \\  & & & & stunnel, such that the distance between \\  & & & transverse SRBs is 1.5 m, the distance \\  & & & between rows is 0.5 m, and the borehole \\  & & & diameter is 100 mm. \\ \hline \multirow{4}{*}{Tunnel arch position} & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\ \end{tabular}
\begin{tabular}{c}  \\ \end{tabular}
\end{table} 
Table 2: Common layout of stress release boreholes (SRBs) in deep hard rock tunnels constructed by the drilling and blasting method. Figure 1: Technical principle of ASRBs in deep hard rock TBM tunnels: **(a)** schematic diagram of the stress concentration characteristics of the surrounding rock under TBM excavation disturbance; **(b)** layout of ASRBs and schematic diagram of the stress release area. was specified for analysis, and its mechanical parameters are listed in Table 3. The maximum principal stress distribution after the application of SRBs was simulated under the initial geostress conditions of \(\sigma_{1}\) = 39.38 MPa, \(\sigma_{2}\) = 31.14 MPa, and \(\sigma_{3}\) = 27.63 MPa. The simulation results show that certain stress concentration areas and stress release areas can be formed around a single SRB (Figure 2a).