Bill Parks has a simple, powerful reply to anyone who says shotcrete can’t be waterproofed:
“Alaskan Way Viaduct.”
This mammoth $3.1 billion project, set to deliver in late 2018, is transforming the waterfront of downtown Seattle with a series of 30 major interrelated construction projects. The headliner: a 2-mile-long highway tunnel carved under downtown Seattle. The project replaces the Alaskan Way Viaduct, an aging highway overpass vulnerable to earthquakes.
Pick Your Poison
Bill Parks, project manager for Sacramento, Calif.-based waterproofer F.D. Thomas, was tasked with several epic assignments, including waterproofing the south tunnel portal, a cut-and-cover section formed with shotcrete. The F.D. Thomas team faced a daunting series of issues, including:
- Meet specifications that called for a clay membrane waterproofing solution
- Work dozens of feet below the water table during one of the rainiest periods on record
- Comply with harsh warranty requirements for near-zero water leakage
- Maintain a hyper-aggressive project schedule.
Parks knew if they could clear one crucial hurdle—changing the original waterproofing specs—he and his team could meet the demanding expectations.
“They wanted us to use a clay-based waterproofing system right off the bat,” Parks recalls. “We said no. We insisted on the Preprufe® SCS system. We were fortunate they changed the specs. That was key. If we had used the other system, it would have been a disaster.”
The 60-foot-deep jobsite was virtually floating in water. Water fountains shooting four feet or higher routinely burst through the mud slab. Secant piles offered only token water resistance. And still it rained and rained.
Was Parks concerned? Not so much.
“As a West Coast company, we’ve put up millions of feet of the Preprufe SCS system up. We haven’t had any issues whatsoever with major leaks or system failure at any level,” Parks reports.
Parks sweeps aside notions that shotcrete cannot be waterproofed. “I’ve heard what the skeptics say. ‘You can’t solve the voids, shadows, and consolidation issues of shotcrete.’ I completely disagree. The Preprufe SCS system takes all those issues off the table,” Parks says.
Preprufe SCS is a pre-applied system engineered for shotcrete linings and is manufactured and sold by GCP Applied Technologies, formerly Grace Construction Products. The easy-to-apply membrane and injected grout bond creates a uniform and continuous waterproofing system, sealing off the structure with a resilient cover and ending lateral water migration.
“If a leak appears,” Parks says, “your chances of immediately stopping it are about 90 percent with Preprufe SCS. With another system you’re at 50-50. You could be chasing that leak for years because of the way water travels.”
While up to two years of work remains on tunnel boring and finishing, the south portal results are outstanding. F.D. Thomas has installed Preprufe SCS to about 400,000 square feet of walls. Verdict: a bone-dry tunnel.
“When waterproofed by an experienced team, shotcrete applications are completely waterproof,” Parks explains. “General contractors, owners, architects, and engineers can definitely specify watertight shotcrete with confidence.”
There’s a $3.1-billion project in Seattle that proves it.