# Key Technology of TBM Excavation in Soft and Broken Surrounding Rock
## 4 Countermeasures for TBM Construction Risk in the Weak and Broken Stratum
### Development of New Equipment  
Gaoligongshan Tunnel, as a key control project of Darui Railway, has the geological characteristics of \"three high and four active\". Dealing with the TBM construction process may involve encounters with the fault fracture zone, mud gushing, rock bursts, and other disasters. The TBM design of the Gaoligongshan main tunnel breaks through the technology of variable cross-section lifting excavation, pre-automatic mixing spraying, and concealed normalization advanced drilling. Practice shows that the innovative design of TBM has played a significant role in the excavation process, and it provides valuable experience for innovative design and the application of TBM in similar geological conditions. Main drive lifting design  
To realize continuous excavation expansion, the TBM needs to raise the drive system while changing the diameter of the cutter head to prevent the machine from sinking after the diameter of the cutter head becomes larger. The TBM bottom shield is rigidly connected to the head frame through bolts. If it is necessary to excavate with variable diameters, first remove the connecting bolts between the bottom shield and the head frame diameter; lift the head frame to the required height through the lifting oil cylinder; fill the steel plate with a corresponding thickness between the head frame and the bottom shield; and, finally, reconnect the head frame and the bottom shield rigidly, as shown in Figure 5.  
Pre-automatic mixing spraying design  
When a TBM passes through a bad stratum, to reduce the collapse and convergence of surrounding rock after it comes out of the shield, a wet spraying manipulator is designed for the steel arch support device at the tail of the main machine's shield to seal the surrounding rock in time. Through structural and spatial optimization, the arc track and rack are added to the steel arch tightening mechanism, and the traveling trolley is meshed with the gear and rack to realize the walking of the wet spraying trolley along the 270\({}^{\circ}\) range of the arc track. The wet spray nozzle is installed on the wet spray trolley, and the distance between the nozzle and the tunnel wall can be adjusted. The wet shotcrete in the L1 area is pumped by a relay. The wet shotcrete is delivered to the two concrete delivery pumps on the right side of the equipment bridge through the mixing pump in the L2 area, and then the concrete is pumped to the wet shotcrete nozzle in the L1 area through the delivery pump on the right side of the equipment bridge. The design effect of the automatic mixing device in the L1 area is shown in Figure 6.  
Figure 5: Schematic diagram of driving lifting device. 3. Concealed normalization advanced drilling technology design  
In the past, the lead drill used on a TBM shared the same track as the roof bolter. The lead drill is installed when in use and removed when not in use. The preparation work is time-consuming and labor-consuming. To avoid delays in the construction period caused by the installation and removal of the advanced drilling rig, the design of the Gaoligong Mountain TBM has a separate track for the advanced drilling rig, and hidden design is adopted. When the advanced drilling rig is not in use, it is hidden in the upper part of the main beam, which does not affect other operations. The design schematic diagram and physical drawing of the hidden advance drill are shown in Figure 7a,b, respectively. The advance drill, propulsion beam, and ring gear beam are designed separately under the main beam platform. The advanced drill pump station is shared with the anchor bolt drill system in the L1 area. During normal tunneling, the lead drill is hidden under the main beam platform with a section of ring gear track beam, and two sections of ring gear track beams are fixed on both sides. When it is necessary to drill in advance, the lead drill and ring gear track beam are raised together through the oil cylinders on both sides and connected with the ring gear beams on both sides to form a whole ring gear.