The Arizona Department of Transportation (ADOT) has adopted new foam injection technology to combat subsidence without digging up road surface, thereby saving time.

The department has used this new technique to combat subsidence along Loop 101 (Pima Freeway) in the Scottsdale area, where it has injected foam.

The foam hardens as it expands and stabilises the soil, lifting the sunken section of road surface.

"Expansion foam isn’t the answer in all cases, but we’ve had some great success in offsetting the effects of ground settlement."

This work has been taken up 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 last work items before a new layer of smooth rubberised asphalt is added.

As well as the present soil-stabilisation work, the Loop 101 widening project includes laying of new lanes and other improvements along an 17.7km stretch of the freeway.

The complete project is expected to be completed by this year.

ADOT infrastructure delivery and operations division director Steve Boschen said: "This is certainly less disruptive than digging up the freeway to do reconstruction work.

"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."