Improving efficiency and customizing solutions for a large-scale tunnel excavation project

Thanks to the combined efforts of many key players, big and small, a new infrastructure project is about to make history.

Seattle’s infamous 2-mile-long tunnel project, built underneath its downtown area to replace the city’s State Route 99 Alaska Way Viaduct, is one step closer to completion. While it’s been a long road, “Bertha,” the largest tunnel boring machine (TBM) at the time that it was built, reached the end of its journey beneath the city in early April.

It took nearly four years for Bertha to break through to the opposite end of the tunnel, excavating approximately 28 dump-truck loads of soil every 25 minutes during the height of its operation.

The Emerald City’s project to replace the aging infrastructure — a major North/South connection through its downtown area — has been a work in progress for nine years. The 60-year-old structure has been suffering from decades of wear and tear, along with the effects of population growth and congestion. As a solution to alleviate some of the traffic, the city decided to replace the viaduct with a double-deck highway tunnel along Seattle’s waterfront.

To realize the vision of a 5-storey-tall underground tunnel, builders needed solutions suited to the demands of earth pressure balance (EPB) tunneling, both to seal the TBM from incoming water and soil and to condition the soils for efficient excavation. BASF contributed several primary products, tunneling expertise and logistics to that end.

As with all massive projects, there were many technical challenges. To overcome one such challenge, BASF teamed up with the Colorado School of Mines to initiate a research program, which aimed to replicate conditions in the Seattle environment by testing chemically enhanced soils. This procedure helped BASF better understand the project’s difficult tunneling conditions and customize the best solutions.

To help make the tunneling project a success, BASF contributed the following construction technologies, among others:

  • Soil conditioners: EPB tunneling requires the correct use of soil conditioners to reduce cutter-head torque and increase advance rates — in other words, the rate at which the TBM moves forward in the tunnel. The more efficiently it advances, the quicker the project can be completed.
  • Tail sealant greases: They are used for sealing against water, soil and annulus grout ingress into the TBM.
  • Annulus grout admixtures: When the segmental lining, made of precast concrete segments, is built inside the TBM, the space between the ground and the segments is called the annulus gap. BASF provided retarders used in the grouting process to affect the setting time of the grout.
  • Polymer injection systems: Injection grouting near the end of the tunnel drive was used for ground consolidation and water control to prevent water ingress into the tunnel and at the portal.
  • Precast concrete segments admixtures: High-performance concrete additives were used to ensure durability and efficient production of the precast concrete segments, such as the MasterGlenium® superplasticizer; MasterFinish®, a finish-enhancing admixture; and MasterLife®, a silica fume mineral admixture.

 

“We’re very excited to have been part of the world’s largest diameter tunnel,” said Jim Lindsay, Regional Business Segment Manager, Construction Chemicals N.A., BASF.

“The sheer magnitude of the project was a technical and logistical challenge, and BASF’s specialized tunneling expertise and logistical infrastructure made it possible to effectively meet the challenges of this landmark project.”

It will still be two years before the highway opens, as crews need to complete the double-decker lanes and other infrastructure inside the tunnel.

“We’re very excited to have been part of the world’s largest diameter tunnel,” said Jim Lindsay, Regional Business Segment Manager, Construction Chemicals N.A., BASF.

“The sheer magnitude of the project was a technical and logistical challenge, and BASF’s specialized tunneling expertise and logistical infrastructure made it possible to effectively meet the challenges of this landmark project.”

It will still be two years before the highway opens, as crews need to complete the double-decker lanes and other infrastructure inside the tunnel.

The Seattle tunnel project is a partnership between the Federal Highway Administration, the Washington State Department of Transportation, King County, the Port of Seattle and the City of Seattle.

If you’d like to learn more about BASF’s involvement in up-and-coming infrastructure projects, watch this video from the Atlantic Summit on Infrastructure and Transportation in Washington, DC.

 

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