Overview
Mixshield and slurry-balance tunnel boring machines (TBMs) drive subway lines, under-river crossings and long-distance utility tunnels. The density difference between supply slurry (fresh) and return slurry (with cuttings) reflects spoil volume and excavation chamber pressure — the primary monitoring parameter for slurry TBM operators worldwide.
Process challenges
- Return slurry carries cobbles and rock chips — extremely abrasive; intrusive sensors wear out fast
- Supply line operates at 1-6 bar — sensors need high-pressure rating
- Compact installation space in shield cab — sensors must be slim
- Ground formations switch abruptly (soil / sand / cobble / rock) — millisecond response required
- Confined-space tunnels make radioactive gauges hard to license
Recommended solutions
| Measurement point | Principle | Models |
|---|---|---|
| Supply (fresh slurry) line | Ultrasonic acoustic impedance | PS7000 |
| Return slurry line | Ultrasonic acoustic impedance + abrasion shield | PS7000 |
| Spoil separator outlet | Ultrasonic | PS7000 |