# Key Technology of TBM Excavation in Soft and Broken Surrounding Rock
## 2 Project Overview
### Analysis of Unfavorable Geological Conditions  
The unfavorable geological conditions of the TBMs tunneling section of the Gaoligongshan Tunnel mainly include high ground stress, fractured ground, high ground temperature, high seismic intensity, dissolvable rock, water gust, etc. 1. High ground stress: The maximum cover of the tunnel is 1155 m, and the regional stress field is relatively high. The relationship among the values of three-dimensional principal stress around the tunnel body in the survey area is vertical principal stress (about 31 MPa) > maximum horizontal principal stress (20-29 MPa) > minimum horizontal principal stress (13-19 MPa). The angle between the dominant direction of the maximum horizontal principal stress and the direction of the tunnel alignment is 12\({}^{\circ}\)-21\({}^{\circ}\), and rock burst and large deformation of soft rock may occur in the tunnel. According to the prediction, the total length of the soft rock large-deformation section of the main tunnel is 3185 m, and the length of the slight large-deformation section is 1435 m; in fractured fault zones, local fault clay is prone to medium-large deformation, with a length of 1750 m.
2. Fractured ground: There will be 20 fractured-extremely fractured rock mass sections (with a total length of 1280 m) in the TBM tunneling section of the main tunnel, and there will be 15 fractured-extremely fractured rock mass sections (with a total length of 980 m) in the TBM tunneling section of the parallel edit. The proportion of Grade IV and Grade V surrounding rock passed through by the whole tunnel is as high as 50%. 3. High ground temperature: In mountain-crossing sections of Gaoligongshan Tunnel, the maximum temperature measured by deep hole drilling is 41 \({}^{\circ}\)C, the maximum temperature at the shoulder surface is 36.8 \({}^{\circ}\)C, and the temperature of the rock mass in the tunnel body section D1K197 + 460- D1K207 + 582 (with a length of 10.122 km) is 27\(\sim\)40 \({}^{\circ}\)C.
4. High seismic intensity: The area is located in the seismic zone of southwest Yunnan, where the intensity of seismic activity is very high and the earthquake frequency is high. The seismic ground motion peak acceleration in the survey area is 0.20 g, and the period of the seismic ground motion response spectrum is 0.45 s. The correlation between the strong earthquakes and the distribution of the active faults is extremely high, and most of the strong earthquakes above Magnitude 6 are distributed along active faults. The site never suffered strong earthquakes in history, but in May 1976, a 7.3 magnitude earthquake occurred in Longling. 5. Dissolvable rock and water gust: In the entrance section of the tunnel, the total length of the Triassic dolomite and the sandwich-type dissolvable rock in Jurassic, Ordovician, Cambrian, and other strata is 1392 m, with the karst weakly to moderately developed. The Silurian limestone and dolomite in the middle of the tunnel are 590 m in length, and the Devonian limestone and dolomite in the exit section of the tunnel are 1330 m in length, with the karst weakly developed. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Lithology and Geological Structure** & **Length/m** & **CAI/(\(\times\)10\({}^{-1}\) mm)** & \
\begin{tabular}{c} **Uniaxial Saturated** \\ **Compressive Strength** \\ **of Rock/MPa** \\ \end{tabular} &
\begin{tabular}{c} **Integrity** \\ **Coefficient of Rock** \\ \end{tabular} \\ \hline Yanshanian granite & 8810 & 3.34–3.59 & 46–65 & 0.25–0.85 \\ Dolomite and limestone mixed with quartz sandstone & 290 & 3.34–4.12 & 60–65 & 0.69–0.78 \\ Level V abnormal belt for geophysical prospecting & 840 & 3.34–5.18 & 8–40 & 0.73–0.86 \\ Limestone and dolomite mixed with quartz sandstone & 460 & 2.46–3.68 & 30–40 & 0.45–0.85 \\ Schist, slate, and phyllite mixed with quartzite, and metamorphic sandstone & 1440 & 2.38–3.53 & 20–40 & 0.45–0.85 \\ Alternated Rock & 140 & 2.00–3.12 & 5–15 & / \\ \hline \hline \end{tabular}
\end{table}