# Numerical Studies on Rockbursts in Tunnels with High In Situ Stresses and Geothermally Rich Areas
## 5 Discussion
### Effect of In Situ Stress
#### 5.2.1 Influence of \(\sigma_{ver}\) and \(\sigma_{hor}\) on the Change in Tunnel Stress  
According to the results presented in Section 4, the junction of the tunnel face and tunnel wall is an area of concentrated stress (rockbursts can easily occur), and the maximum compressive stress of SP#Left is larger than that of SP#Up and that of SP#Down. However, there is a difference observed in the influence of the in situ stress change on the tunnel stress distribution by comparison, and the law of stress distribution is related to the stress concentration area position; thus, only the influences of the in situ stress change on the stress concentration area position, the maximum compressive stress (\(t=0\) h) and the maximum tensile stress (\(t=24\) h) are discussed. Figure 13a shows the maximum compressive stress at \(t=0\) h and maximum tensile stress at \(t=24\) h for the surrounding rock at different vertical stresses (\(\sigma_{ver}\)). The selected stress values in the two directions are always maintained (\(\sigma_{ver}>\sigma_{hor}\)), and the maximum compressive stress of SP#Left is always larger than that of SP#Up and that of SP#Down in this case. The maximum compressive stress point is at the junction of SP#Left on the tunnel wall and SP#Tunnel face. Figure 13a shows that the larger \(\sigma_{ver}\) is, the greater the maximum compressive stress of the stress concentration area at \(t=0\) h and the more easily rockbursts occurs. The larger \(\sigma_{ver}\) is, the greater the maximum tensile stress at \(t=24\) h, and the more likely the rock of the tunnel face is to fail (see Section 4). Figure 13b shows the maximum compressive stress at \(t=0\) h and maximum tensile stress at \(t=24\) h for the surrounding rock at different horizontal stresses (\(\sigma_{hor}\)). Because both curves have turning points, they are analyzed separately here, and the maximum compressive stress is analyzed first. Figure 13b shows that although the horizontal stress (\(\sigma_{hor}\)) increases, as the ratio of horizontal stress to vertical stress changes(\((\sigma_{ver}>\sigma_{hor})\rightarrow(\sigma_{ver}=\sigma_{hor})\rightarrow(\sigma_{ver}<\sigma_{hor})\)), the location of the stress concentration point at \(t=0\) h also changes (the junction of SP#Left on the tunnel wall and SP#Tunnel face \(\rightarrow\)the junction of the whole tunnel wall and SP#Tunnel face \(\rightarrow\) the junction of SP#Up and SP#Down on the tunnel wall and SP#Tunnel face). When \(\sigma_{ver}=\sigma_{hor}\), the maximum compressive stress is at its minimum, and rockbursts are less likely to occur. Additionally, with increasing horizontal stress (\(\sigma_{hor}\)), the ratio of horizontal stress to axial stress changes (\((\sigma_{axi}>\sigma_{hor})\rightarrow(\sigma_{axi}=\sigma_{hor})\rightarrow( \sigma_{axi}<\sigma_{hor})\)). When \(\sigma_{axi}=\sigma_{hor}\), the maximum tensile stress is at a minimum at \(t=24\) h, and rock is less likely to fail. In addition, the simulation results show that the larger the difference between \(\sigma_{ver}\) and \(\sigma_{hor}\) is, the larger the maximum compressive stress at \(t=0\) h and the more likely rockbursts are to occur. Similarly, the larger the difference between \(\sigma_{axi}\) and \(\sigma_{hor}\) is, the larger the maximum tensile stress at \(t=24\) h and the more likely rock is to fail.