Principle of Cutter Replacement for TBM

Category: News

Time: 2026-10-22

Summary:

1. High-Temperature Resistant Cutters
During the TBM (Tunnel Boring Machine) excavation process, the disc cutter generates frictional heat due to friction with the rock. This causes its internal temperature to rise, resulting in temperature gradients and uneven thermal expansion. The continuous rolling pressure of the cutter against the rock creates alternating internal thermal stress and strain. This highly easily leads to fatigue damage of the cutter, causing the cutter ring to fracture. At the same time, micro-cracks generated in the surface layer of the cutter ring by the alternating thermal stress and strain will also accelerate cutter ring wear. Furthermore, as the temperature rises, the performance of internal components such as bearings and seals will be significantly affected. This causes a decrease in the viscosity of the lubricating oil, potentially leading to lubricant failure, reducing the load-bearing capacity of the cutter, and shortening its service life. The high-temperature resistance of high-temperature resistant cutters primarily depends on the high-temperature capabilities of the internal floating seals and lubricating media within the cutter.
2. High Water-Pressure Resistant Cutters
With the extensive development of underground space in recent years, shield tunneling operations have gradually increased, particularly for river-crossing and sea-crossing tunnels. Currently, deep-buried, high-water-pressure shield operations—such as the Shiziyang Tunnel, Wuhan Sanyang Road Tunnel, Shantou Bay Tunnel, and Mawan Tunnel—have seen maximum water pressures exceeding 10 bar. The pressure differential capacity of conventional disc cutters is 3 bar. When operating in high-water-pressure environments, high-pressure resistant cutters must be used. Cutters suitable for high-water-pressure environments primarily require high stability of the cutter's sealing performance under external high-pressure conditions to ensure normal operation. The key focus is to break through the sealing technology of disc cutters under high-water-pressure environments.
2.1 Principle of High Water-Pressure Disc Cutters
A cavity is created at the center of the cutter shaft, which communicates with the interior of the disc cutter. At the same time, a movable piston is installed inside the cavity. When the disc cutter operates in a high-water-pressure environment, the internal pressure of the cutter is modified by adjusting the volume of internal air. This achieves a dynamic balance with the environmental pressure of the excavation working face, ensuring the operational stability of the cutter's rotation. According to the PVT (Pressure-Volume-Temperature) properties of gases, by adjusting the internal volume of the cutter the required internal pressure of the disc cutter is obtained. This ensures that the pressure differential between the inside and outside of the cutter does not exceed the limit of the seal's pressure differential capacity. When installing this type of disc cutter, it is generally required that the internal cavity of the cutter be fully filled with lubricating oil.
2.2 Types of High Water-Pressure Disc Cutters
High water-pressure disc cutters mainly come in two types: the movable piston type and the inflatable bladder type. The movable piston type can achieve a maximum internal pressurization of 6 bar. Combined with the floating seal's ability to withstand a safe pressure differential of 3 bar, this type of high water-pressure disc cutter can meet the environmental requirements of excavation conditions up to 9 bar.
• 刀圈: Cutter Ring • 磁铁: Magnet • 刀毂: Cutter Hub • 端盖: End Cap • 刀轴: Cutter Shaft • 挡圈: Retaining Ring • 轴承: Bearing • 密封座: Seal Seat • 浮动密封: Floating Seal • 堵丝: Screw Plug • 大螺母: Large Nut • 阀芯: Valve Core • 轴承隔环: Bearing Spacer Ring • 阀芯堵头: Valve Core Plug
  • 刀圈: Cutter Ring
  • 磁铁: Magnet
  • 刀毂: Cutter Hub
  • 端盖: End Cap
  • 刀轴: Cutter Shaft
  • 挡圈: Retaining Ring
  • 轴承: Bearing
  • 密封座: Seal Seat
  • 浮动密封: Floating Seal
  • 堵丝: Screw Plug
  • 大螺母: Large Nut
  • 阀芯: Valve Core
  • 轴承隔环: Bearing Spacer Ring
  • 阀芯堵头: Valve Core Plug
2.3 Chamber Opening under Pressure Technology in High Water Pressure-Highly Permeable Strata
In shield tunnels crossing rivers and seas, when the shield machine is shut down, it is often located in complex strata with high water pressure (>0.5 MPa) and high permeability (permeability coefficient >10⁻² cm/s). Such strata do not possess the conditions for atmospheric chamber opening operations. Therefore, it is impossible to avoid intervention operations inside the chamber under pressure. Changing cutters under pressure carries high risks, slow progress, and poses significant health hazards to personnel. Chamber interventions under pressure can be divided into two types: conventional compressed air operations and saturation diving operations under pressure. The former is suitable for conditions with shallow depths, relatively low pressures, and short operating durations. The latter is suitable for conditions with great depths, high air pressures, and long operating durations.
2.3.1 Conventional Compressed Air Chamber Interventions under Pressure
The Nanjing Yangtze River Tunnel is a typical early project in China that adopted conventional compressed air chamber opening and cutter changing under pressure technology. When the shield tunneled to a depth of 53.25 m beneath the riverbed, severe wear on the cutterhead and cutters occurred, making further excavation impossible. To ensure the gas-tightness of the stratum during compressed air operations, the project first allowed a large amount of low-density, low-viscosity pure bentonite slurry to penetrate the excavation face. Then, the slurry inside the pressure chamber was replaced with a mixed slurry of bentonite and clay to form a dense, gas-tight slurry cake. After the slurry cake formed, the slurry level was lowered by 3 m and replaced with compressed air. Before replacing the cutters, the operators entered the man lock to undergo pressurization, and subsequently performed the cutter replacement work inside the slurry chamber. The effective operation time for each session was 45 to 60 minutes, with a working efficiency of approximately 50%.
Additionally, the prevention and treatment of decompression sickness (barotrauma/bends) among operators under pneumatic conditions is another key issue for this technology. Since cutter replacement via chamber opening under pressure requires operators to undergo a pressurization process (generally 10–20 min) for every task, they must also undergo a decompression process (generally 2–3 h) inside the man lock before exiting after completing cutterhead and cutter inspection and replacement. Frequently undergoing pressurization and decompression processes easily leads to decompression symptoms in operators. Therefore, conventional compressed air chamber opening and cutter changing technology is not very suitable for cutter replacement operations with a large workload.
2.3.2 Saturation Diving Chamber Interventions under Pressure
Cutter replacement via saturation diving requires specific equipment on the shield machine, such as a saturation hyperbaric living chamber and a personnel transfer lock (shuttle). During the cutter replacement period, operators only need to undergo a single pressurization process. They rest and wait in the hyperbaric living chamber and perform work in front of the cutterhead excavation face. After the work is completed, they likewise only need to undergo a single decompression process to return to atmospheric pressure. Therefore, compared to conventional compressed air cutter replacement, saturation diving cutter replacement is applicable to strata with higher water and earth pressures. At the same time, it eliminates the need for multiple pressurizations and decompressions, significantly improving work efficiency. When using saturation diving for cutter replacement operations, a single working shift can last up to 6 to 8 hours. The working efficiency is 8 to 10 times that of conventional operations under pressure. Furthermore, the saturation chamber can accommodate personnel for about 3 weeks, effectively reducing the probability of contracting decompression sickness.

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