Seattle Tunnel Partners (TBM Bentonite Plant)



Seattle Tunnel Partners
SR99 Viaduct Replacement Tunnel Project
Seattle, WA

180 m3/hr



  • Conceptual Design
  • Mechanical Engineering
  • Fabrication of all Equipment
  • Commissioning
  • On-Site Training and Site Support


  • 108 m3 Capacity Bentonite Silo
  • Screw Conveyor
  • 20’ Heated Container
  • Bentonite Loss-In-Weight Feeder
  • Two 6×8-13 Centrifugal Water Pumps
  • 6” Venturi Mixer
  • Automated PLC/MCC Control System
  • Pneumatic System
  • Two 150 m3 Hydration Tanks with Circulation
  • Two 150 m3/hr Progressing Cavity Pumps

As a safety precaution to operating the world’s largest EPB tunnelling machine, Seattle Tunnel Partners wanted to be able to quickly flood the machines massive excavation chamber with hydrated bentonite if a hyperbaric intervention was required. Team Mixing Technologies Inc. was awarded the contract to design and supply this system.

The fully automated bentonite plant utilizes a 6” venturi mixer capable of producing 180 m3/hr of bentonite slurry. Two holding tanks, 150 m3 capacity each, allow the bentonite to hydrate. These tanks incorporate radial eductors along with a centrifugal pump to circulate the bentonite within the tank.

Each tank has a dedicated 150 m3/hr capacity progressing cavity pump to transfer the hydrated bentonite to the TBM’s holding tank via an 8” pipeline.

Hydrated bentonite is also pumped to the grout plant where it is used in the preparation of the “A” component grout. The use of hydrated bentonite significantly reduces grout bleed.