From Realtà Mapei n° 33 - 4/29/2021

Tunnel Teamwork

MAPEI UTT helps to complete Seattle’s Bellevue Tunnel
Overview: Three years ago, work began on constructing an underground light rail tunnel in downtown Bellevue, Washington. This project represented the first time that MAPEI’s Mapelastic TU System synthetic membrane was used for major tunnel construction in the United States. MAPEI was successfully chosen over the competitors, even though it had not worked on previous projects of its type in America. This project is also special as it was the last one that MAPEI’s Bill Allen worked on before his untimely passing.

The downtown Bellevue tunnel (E330) is a soft-ground, 1,985-foot (605-m), sequential excavation method (SEM) tunnel located in Bellevue, WA. The E330 is part of Sound Transit’s larger East Link program that provides 14 miles (22.5 km) of light rail connecting the southern part of Seattle to Redmond, WA.

Sound Transit awarded Guy Atkinson Construction a $121 million contract to construct an underground light rail tunnel (the E330) in downtown Bellevue. The E330 contract is one of multiple projects that will complete the East Link light rail extension, which will run from downtown Seattle to Redmond.

The downtown Bellevue tunnel begins at the south portal near 112th Avenue SE and Main Street. It then runs under 110th Avenue NE for about one-half of a mile (0.80 km) and turns east near NE 6th Street toward the north portal – immediately adjacent to Bellevue City Hall and the Bellevue Transit Center.

The E330 tunneling operation included about 1,985 linear feet (605 m) of SEM tunnel construction, as well as tunnel pre-support, groundwater control, waterproofing, final lining, tunnel walkways, a center dividing wall, embeds and conduits, and a mid-tunnel access shaft and adit.

MAPEI’s Underground Technology Team (UTT) – which is recognized for its worldwide expertise, its customized products, and its dedicated and professional staff – was awarded the design, bid and build contract for the tunnel.

MAPEI products on the jobsite

The MAPEI coordinator for the project was the late Bill Allen, who served as Business Development Manager for Tunneling for MAPEI UTT North America. He was not only a valued member of the UTT team and an expert in shotcrete, but he was also an American Concrete Institute examiner for nozzleman certification. Allen’s skills came in handy due to the tunnel specifications calling for the application of shotcrete over three layers of Mapelastic TU System synthetic membrane – the first time that this product was used in a commercial application in the United States.

From the very beginning, the job presented challenges. The substrate was not smooth and, although that was not a major issue, the water infiltration that plagued the site was. According to Allen’s report from November 2018, “It has been a struggle to deal with water ingress, water seepage and damp areas. We have learned that the substrate must be dry to successfully install Mapelastic TU.”

The general contractor, Guy Atkinson Construction, ran a crew of six to 10 per shift. MAPEI UTT was on site for the 2-p.m.-to-midnight shift, as that was when the patching operations were finished and the application work began.

The application process followed roughly the same schedule for the entire project, according to Monica Rourke, MAPEI UTT’s North America Chemical Grout Injection Manager – Waterproofing as well as Allen’s colleague on the team and the one who took over after his passing. Rourke said the general contractor would first patch the very rough, and many times wet, surface. Then Mapelastic TU was sprayed in three coats; the first coat was white, the second coat was blue/green, and the third coat was again white. Lastly, once Mapelastic TU had cured, the shotcrete was sprayed using a special two-component pump.

“The crew learned how to spot critical areas in the application – the water would darken the substrate – and used the colors to distinguish leaks coming through the sprayed surface,” Rourke explained. These areas were then marked and patched, and the process would begin again.

At one point in the installation, “the general contractor damaged the Mapelastic TU when pulling off the forms at the joint,” Rourke said. But, MAPEI had a solution. “The Mapelastic TU was patched using Mapeproof AL NA and also by patching over with a layer of Mapelastic TU,” she continued.

With MAPEI products waterproofing the invert and walls, the tunnel opened in the late summer of 2020. “This is not only the first use of Mapelastic TU in the U.S., but it is also such a lasting tribute to the hard work and dedication of our team member, Bill Allen,” Rourke said.

Technical data

East Link Light Rail, Bellevue Tunnel – Bellevue, WA, USA
Years of construction: 2017-2020
Years of MAPEI involvement: 2019-2020
MAPEI coordinators: Bill Allen (in memoriam), Monica Rourke and Enrico Pavese
Project owner: Sound Transit
General contractor: Guy Atkinson Construction
Installer company: F.D. Thomas, Inc.
Project manager: Bill Packs
Photographers: Monica Rourke and Stuart Isett
Project size: 1,985 linear feet (605 m) of tunnel construction
Where MAPEI products were used: Mapelastic TU System synthetic membrane was applied in three coats onto the walls of the tunnel. Mapeproof AL NA was used for any necessary patching.
Challenges: Loss of team member halfway through job; uneven substrate; damage caused by removal of forms
MAPEI Products: Mapelastic TU System and Mapeproof AL NA

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