Tunnel Teamwork

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.