With its current park-and-ride facilities operating beyond capacity, Intercity Transit of Lacey, Wash., decided to make effective use of public land by developing a new park-and-ride facility atop a retired landfill.
A feasibility study conducted in 2008 confirmed that differential settlement would continue as waste materials further decomposed. Therefore, soil stabilization and pavement reinforcement were critical elements of the project.
Landfill surface heights ranged from 25 ft to 40 ft. Also, an aged and outdated methane gas collection system was in place, so temporary modifications were made to the collection system and to the existing landfill cover before preloading the site with 148,000 tons of fill.
Solution
The project was completed in two phases. Phase I (2009–2011) included site preparation, gas collection and subsurface compaction.
“We completed the preload in two phases,” said Bob Holcomb, P.E., project engineer and project manager at KPFF, the project’s design engineer. “One-half of the clean fill material was placed and allowed to settle for six months. The remaining half was then placed and allowed to settle for the same amount of time.”
Once compaction was complete, Phase II began in 2012 with layered construction using a geogrid-stabilized subgrade.
Holcomb said that a liner and fill had been placed when the landfill was closed nearly 25 years ago. “We had to maintain a 6-in. layer of fill between the original liner and the new geogrid as a cushion layer for the liner,” he said.
Completed in four phases to accommodate the most efficient movement of materials around the site, the geogrid installation was a “straightforward job,” said Chris Hansen, project manager for Scarsella Brothers.
John Jaggi, Scarsella project superintendent, had never worked with the product before, but, “On the second lift, it took my worries away. From beginning to end, installation was a smooth ride, without any wave action. It’s easier to pin and secure than a solid [geotextile] material.
“I was thoroughly impressed,” Jaggi said. “It was rock-solid how the layers linked together, like walking on a gravel pit floor.”
Holcomb had a similar observation. “Once the TriAx Geogrid went down, it was solid,” he said. “The vibrations ended.”
In areas supporting commuter lanes and parking, a single layer of TriAx Geogrid was installed. A 12-in. layer of fill was placed next, followed by a geomembrane liner, an additional 30 in. of fill and paving. The paving featured 4 in. of crushed surfacing topped with 3 in. of asphalt.
The areas supporting bus traffic were constructed differently: Twelve in. of fill were placed over the existing liner, followed by the geomembrane. Within the final 60 in. of fill, two layers of TriAx Geogrid, spaced 16 in. apart, were installed. Paving included a 3-in. layer of asphalt, reinforced with the GlasGrid System and topped with 3 in. of surface asphalt. While concrete is typically used in bus lanes and turnarounds, asphalt was specified for the entire project due to its flexibility in the event of differential settlement. Like the TriAx Geogrid, the GlasGrid System product was sourced through the Fife, Wash. office of ACF West, Tensar’s regional distributor.
A Scarsella crew of five installed the GlasGrid System with its pre-applied tack film. “I was skeptical,” Jaggi said, “but it tacked right down. It was easy to work with, and we didn’t have one spot that didn’t tack. On the second roll, it was as if the crew had been working with it forever.”
The crew completed the installation in about five hours.
Results
After five years of planning and development, the Hawk’s Prairie facility opened in January 2013. The lot increases the South Puget Sound region’s park-and-ride capacity by more than 75%, helps to relieve a heavily congested segment of Interstate 5 and makes effective, sustainable use of public land.
In May 2013, the American Public Works Association chose the Hawks Prairie facility as Washington State’s Project of the Year in the $5- to 25-million transportation category.
Criteria included construction management, safety performance, community relations, environmental vigilance and more.
