What are the procedures for handling pressurized slurry during cutterhead maintenance in a Slurry TBM?

Handling pressurized slurry during cutterhead maintenance in a Slurry TBM requires strict safety protocols and procedures to prevent uncontrolled releases, maintain face stability, and protect personnel. The first step is to reduce the slurry pressure in the excavation chamber to a safe level. This is typically done by gradually pumping the slurry out of the chamber while monitoring the face stability. The pressure is reduced to a point where it is safe for personnel to enter the chamber, but still sufficient to provide some support to the tunnel face. Next, the cutterhead is locked in place to prevent it from rotating during maintenance. Mechanical locking devices or hydraulic brakes are used to secure the cutterhead. After the cutterhead is locked, a sealed access chamber, or hyperbaric chamber, is connected to the cutterhead housing. This chamber allows personnel to enter the cutterhead area while maintaining a controlled pressure environment. The pressure inside the access chamber is gradually increased to match the slurry pressure in the cutterhead housing. This equalization of pressure prevents slurry from rushing into the access chamber when the access door is opened. Personnel entering the access chamber are equipped with specialized protective gear, including respirators and waterproof suits, to protect them from the slurry. Before opening the access door to the cutterhead, the slurry circulation system is shut down and isolated to prevent accidental start-up. Maintenance work is then performed on the cutterhead, such as replacing worn cutters or repairing damaged components. After the maintenance work is completed, the access door is closed and sealed. The pressure in the access chamber is gradually reduced to atmospheric pressure, allowing personnel to safely exit. The slurry circulation system is then restarted, and the TBM is ready to resume tunneling. 'Slurry TBM' is a type of tunnel boring machine that uses a slurry to support the excavation face. 'Cutterhead' refers to the rotating front part of the TBM fitted with disc cutters. 'Hyperbaric chamber' is a sealed chamber that can be pressurized to simulate the pressure conditions inside the TBM.