ADOT takes high-tech approach when freeway needs a lift

PHOENIX ‒ When a section of freeway settles a bit, taking a high-tech approach to the repair work allows the Arizona Department of Transportation to give the roadway a lift without digging up the pavement.

That’s now the case along the Loop 101 (Pima Freeway) in the Scottsdale area, where ADOT is injecting a foam that hardens as it expands to stabilize the soil and lift the pavement. Crews have removed a minor roadway dip without the disruption of digging up and replacing part of the freeway.

The foam injections are being done as part of the ongoing ADOT project to widen and improve Loop 101 between Shea Boulevard and Loop 202 (Red Mountain Freeway). Repairing the depression in the freeway’s northbound lanes near McDonald Drive is one of the project team’s last work items before completing the addition of a new layer of smooth rubberized asphalt in that area.

“This is certainly less disruptive than digging up the freeway to do reconstruction work,” said Steve Boschen, director of ADOT’s Infrastructure Delivery and Operations Division. “It is a high-tech fix when it comes to long-term ground settlement beneath a freeway. Expansion foam isn’t the answer in all cases, but we’ve had some great success in offsetting the effects of ground settlement.”

Over time, ADOT and contractors have used the expansion foam at other freeway locations where the ground and pavement have settled. It has been used a number of times to lift concrete slabs on either end of freeway bridges. As the foam is injected beneath the freeway, it hardens as it expands and lifts the pavement while stabilizing the soil to guard against future settlement.

“It’s already made a noticeable difference with the dip that drivers may have noticed as they traveled northbound on Loop 101 near the Arizona Canal crossing north of McDonald Drive,” said Dan Haskins, ADOT's resident engineer on the Loop 101 widening project. “We’re able to work during overnight hours with lane closures. The contractor drills very small holes in the freeway pavement. Crews are then able to run narrow hoses to a depth underground where open space in the soil can be filled with the expansion foam. In this case we’re going as far as 30 feet beneath the freeway.”

Before the foam injection is scheduled, ADOT geotechnical staff members have the job of examining the area where the ground beneath the freeway has settled to determine if the use of the foam is the recommended course of action. More advanced soil testing is then done using equipment to map the ground where settling has occurred. That helps give crews the information they need to inject the foam and stabilize the soil.

The Loop 101 widening project between Shea Boulevard and Loop 202 is adding new outside lanes and other improvements along an 11-mile stretch of the freeway. In addition to the current soil-stabilization work near the McDonald Drive interchange, crews are adding a new top layer of smooth rubberized asphalt along the freeway in a series of weekend closures. The entire project is scheduled for completion by this fall.