INDUSTRY 11

Tunnel Boring (TBM)

11 / TUNNELING

Supply and return slurry density on mixshield / slurry-balance TBMs — monitors face support pressure and spoil separation efficiency.

1 applicable products 2 application cases

See cases Talk to an engineer

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

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

Slurry density comparison measurement for mud delivery/mud discharge · Excavation face balance control

In tunnel‑boring machine (TBM) construction, the density difference between the slurry supply and discharge lines is a critical parameter for assessing excavation face pressure balance and providing early warnings of blow‑ups or collapses. However, conventional differential‑pressure, tuning‑fork, and gamma‑ray concentration meters are prone to wear and clogging in abrasive, gravel‑laden slurries, pose radiation safety risks, and suffer from significant cumulative measurement errors in dual‑channel setups. The PS7000 series ultrasonic acoustic impedance slurry density meter is deployed in pairs, synchronously installed on both the supply and discharge pipelines; it is non‑nuclear, erosion‑resistant, and calibrated using the same model, delivering a density difference accuracy better than ±0.5% and enabling real‑time muck volume calculation and precise control of the excavation face.

View case

Slurry density meter · PS7000

On-line Cement Slurry Density Measurement in Oil-Well Cementing

Cementing operators struggled with real-time density control in narrow-pressure-window wells due to inaccurate Coriolis and hazardous radioactive meters. The PS7000 online slurry density meter delivers stable, accurate 1.0–3.0 g/cm³ measurement during on-the-fly mixing, enabling reliable automatic density control.

View case

Selection support for this industry

Guides

All guides →

Comparisons

All comparisons →

Industry FAQ

Which meter for TBM (tunnel boring machine) slurry balance?

The mud–water balance density measurement in tunnel boring machines is a key parameter for stabilizing the excavation face.

Typical operating conditions:

Inflow slurry density: 1.05–1.20 g/cm³;
Outflow slurry density: 1.20–1.40 g/cm³ (containing cuttings);
The slurry contains coarse sand and gravel with particle sizes ≤ 50 mm;
Severe on-site vibration, high humidity, and heavy condensation.

We recommend the PS7000 ultrasonic acoustic impedance concentration meter:

Flanged direct‑insertion design with a non‑contact probe, eliminating wear;
Sapphire probe resistant to sand and gravel erosion;
Chirp algorithm suppresses bubble interference;
IP65 rating; explosion‑proof ExdⅡCT6Gb optional;
4–20 mA + Modbus connectivity to the TBM’s main PLC, enabling real‑time feedback of the inflow–outflow density difference to support chamber pressure adjustment.

All FAQs

Other industries

Non-ferrous Mining Power Emission Control Chemical / Fine Chemical Pharma / Biotech