How does a tunnel boring machine rotate?
I. Rotation method of shield machine
1. Rotation of cutter head
- The shield machine mainly excavates tunnels through the cutter head installed at the front of the shield main body. The rotation of the cutter head is driven by a motor. The motor transmits power to the drive shaft of the cutter head through devices such as a reducer, so that the cutter head can rotate at a certain speed. Generally speaking, the rotational speed of the cutter head can be adjusted according to different geological conditions and tunneling requirements. For example, when tunneling in soft soil layers, the rotational speed may be relatively high to ensure cutting efficiency; while in hard rock strata, the rotational speed may be appropriately reduced while increasing the torque to prevent excessive wear of the cutter head and cutting tools.
- The rotation direction of the cutter head can also be adjusted according to the actual construction situation. Usually, the cutter head rotates clockwise. However, in some special cases, such as dealing with uneven wear of cutting tools or to change the discharge direction of muck, the cutter head can also rotate counterclockwise.
2. Steering of shield body
- During the tunneling process, the shield machine needs to turn to follow the designed route. This is achieved by controlling the asynchronous extension or retraction of the thrust jacks. Multiple thrust jacks are arranged around the shell of the shield machine. When turning is required, the operator will control the jacks on the inner side of the turning direction to slow down or retract the extension speed, while the jacks on the outer side extend normally. In this way, a certain steering angle can be generated for the shield machine body. At the same time, an overcutting device (if available) of the cutter head will also be combined to assist in turning. The overcutting device can cut more soil on the side where turning is required, creating better conditions for the turning of the shield machine.
II. Rotation method of TBM (Full Face Rock Tunnel Boring Machine)
1. Rotation of cutter head
- The principle of cutter head rotation of TBM is similar to that of shield machine. It is also driven by a powerful motor through the transmission system. However, since TBM is mainly used for hard rock tunneling, its cutter head requires higher torque. The motor and transmission system must be able to provide sufficient torque to drive the cutting tools to cut into hard rock. Generally, a driving method with high torque and low rotational speed is adopted. For example, in some large TBM equipment, the rotational speed of the cutter head may only be a few revolutions per minute, but the torque can reach several thousand kilonewton-meters.
- The drive system of the TBM cutter head also has a powerful braking device. This is because if sudden rock fracture zones or other abnormal conditions are encountered during hard rock tunneling, the cutter head rotation needs to be stopped in time to prevent damage to the cutting tools and machine failures.
2. Steering of machine body (for open-type TBM)
- When an open-type TBM steers, it is mainly achieved by adjusting the position of the support shoes. The support shoes are devices used to support the TBM body and provide reaction force. When turning is required, the TBM will first retract some support shoes, and then move the body in the predetermined direction through the propulsion system. The support shoes will be re-extended at the new position to realize the steering of the machine body. For shielded TBMs, the steering method combines the control of the shield propulsion jacks and the adjustment of the support shoe positions, similar to the steering method of shield machines. By controlling the actions of jacks at different positions, the tunneling direction can be changed.