## 3 Roadway Deformation Characteristics
### Rock Mass's Zonal Disintegration around the Roadways  
Excavation of the roadway in the primary rock mass destroyed the original stress balance of the surrounding rock and redistributed the stress. On one hand, its radial stress decreased, and the tangential stress increased, which led to stress concentration. On the other hand, the surrounding rock stress state changed from triaxial to approximately biaxial, and the rock strength decreased. If the concentrated stress was less than the declined rock strength, the surrounding rock would carry itself and maintain an elastic state, that is, the support was unnecessary. Otherwise, the surrounding rock would gradually crack from the periphery to the inside, until it reached another new triaxial stress equilibrium state. At this time, an annular fractured zone occurred around the excavation space, which was the broken rock zone. Owing to the fact that the rock mass's mechanical properties were seriously  
Figure 8: Support failure modes: (**a**) Bolt pulled out and slipped, (**b**) Wire mesh twisted and snapped, (**c**) Shotcrete cracked and extruded, (**d**) U-shaped steel extruded and bent. influenced by the stress environment, the rock with an elastic state in the shallow part displayed elastic-plastic or plastic deformation characteristics in the deep area, and the convergence deformation mechanism of the deep roadway was quite different from that of the shallow roadway. Hence, the distribution characteristics of the broken rock zone of the deep roadway were more complex, and accurately grasping the range of the broken rock zone was crucial for support selection. Therefore, four sections in the study area were selected to conduct the broken rock zone test, as shown in Figure 4. Four measurement points were chosen for each section, two points on the spring line and two points on the spandrel. In order to improve the efficiency, a single-emission and double-receiving measurement method based on the ultrasonic wave was adopted, as shown in Figure 9. Waves emitted by the acoustic emission transducer T slid along the wall of the borehole, and they were then refracted back into the holes and received by the receiving transducers \(R_{1}\) and \(R_{2}\). The calculation formula of the rock mass's longitudinal wave velocity \(V_{p}\) is as follows [34]:  
\[V_{p}=\frac{\Delta L}{t_{2}-t_{1}}, \tag{1}\]  
where \(\Delta L\) is the distance between the two receiving transducers and \(t_{1}\) and \(t_{2}\) are the times when transducers \(R_{1}\) and \(R_{2}\) receive the wave, respectively. The rock mass integrity is characterized by the integrity coefficient \(K_{v}\) of the rock mass, which is calculated as follows:  
\[K_{v}=(\frac{V_{p1}}{V_{p2}})^{2}, \tag{2}\]  
where \(V_{p1}\) is the rock mass's longitudinal wave velocity and \(V_{p2}\) is the intact rock's longitudinal wave velocity. The intact marble's longitudinal wave velocity in the test roadway was approximately 6.5 km/s. Based on the national standard, which classifies the rock mass in engineering (GB50218-94), the relationship between the rock mass integrity indicators \(K_{v}\) and \(V_{p}\) is shown in Table 3. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Rock Mass Integrity** & **Excellent** & **Good** & **Medium** & **Poor** & **Broken** \\ \hline \(K_{v}\) & \(>\)0.75 & 0.75–0.55 & 0.55–0.35 & 0.35–0.15 & \(<\)0.15 \\ \(V_{p}\) (km/s) & \(>\)5630 & 5630–4820 & 4820–3845 & 3845–2517 & \(<\)2517 \\ \hline \end{tabular}
\end{table} 
Table 3: Relationship between the rock mass integrity, \(K_{v}\) and \(V_{p}\). Figure 9: Operation principle of the single-emission and double-receiving measurement method.