If you’ve ever been involved in tunnel boring operations, you know that everything underground has to be tough, especially the seals. But not every seal is the same—and not every part of the shield tunneling machine needs the same kind.
So, what kinds of seals are typically used in a TBM (Tunnel Boring Machine)? Let’s walk through it.
1. Main Bearing Seals
These are critical. The main bearing rotates
constantly and is exposed to soil, slurry, and pressure. Seals here usually
combine multiple lip structures with reinforced backing. Often made from
high-performance elastomers like FKM or HNBR, they also integrate spring
elements to maintain pressure against the shaft.
2. Tail Seals
Installed at the end of the shield machine, tail seals
prevent water and soil from entering the machine’s interior. These seals are
submerged in grout or grease and often use multi-stage sealing rings made of
rubber and metal. The combination of several sealing layers creates a barrier
even under uneven pressure.
3. Hydraulic System Seals
TBMs rely heavily on hydraulic actuators for
steering, thrust, and tool manipulation. These seals include O-rings, rod seals,
and wipers, typically made of NBR or polyurethane, designed to handle fluid
pressure and contamination.
4. Wire Brush Seals
Though not a “seal” in the traditional rubber sense,
wire brushes are installed around rotating parts like cutterheads. They help
prevent particles from reaching sensitive areas and often act as the first
barrier in a multi-sealing setup.
Common Questions From TBM Operators
Q1: Do all TBMs use the same seal
types?
Not always. The type and configuration depend on the size of the
machine, soil conditions, and project design. A slurry shield and an earth
pressure balance machine may differ in their sealing systems.
Q2: Why do seals fail underground?
Common causes include incorrect
material choice, improper installation, wear from abrasive soils, or loss of
grease. Monitoring and proper maintenance are key to longer service life.
Q3: Can seals be replaced without disassembling the whole machine?
Some
external seals like wire brushes or tail seal segments can be accessed during
maintenance windows. However, replacing internal seals like the main bearing
seal often requires more extensive procedures.
When specifying tunnel boring machine seals, it’s important to consider the operating environment, movement type, pressure, and fluid exposure. Choosing the appropriate sealing solution can help maintain machine efficiency and support safe tunneling progress from start to finish.
