Last August, the area was hit by numerous large slips that severed a vital Northland transport link. A remote 13-kilometre stretch of road now bristles with 200+ sensors, forming one of the most concentrated sensor networks ever deployed by WSP.
Eighty-four locations have been equipped with ground movement sensors. Sixteen locations monitor soil moisture. Rain gauges measure volume and intensity of rainfall. Every day, this extensive network of sensors registers seven million data points, which feed into a Trigger Action Response Plan (TARP) that calculates the real-time risk of ground movement.
WSP principal instrumentation engineer Mike Lusby says the sensor information is vital for contractors and geotechnical engineers involved in repairing six critical slips along the route.
"We've developed the TARP system to send electronic alerts and activate loud warning sirens. The TARP is colour-coded, with blue indicating low risk, orange being medium risk, and red high risk. The lights are at start of each location, letting workers know the risk level before entering. Sirens sound whenever the colour changes, alerting workers to changing conditions."
Since going live last October, Mike says the sirens have sounded multiple times, including one instance when a tension crack formed near a sensor. If there’s been 50mm or more of rain within a 24-hour period, the TARP level is automatically raised. If a sensor detects significant ground movement between readings, the sirens will sound.
Sending data out from the remote and inhospitable area is challenging due to the lack of cell phone coverage and power. But shortly after the gorge was closed, WSP's instrumentation team successfully set up real-time data transmission using advanced wireless techniques.
The sensors deployed in the area were prototyped in-house at WSP. Developed for slip movement projects and slope monitoring along railway lines, WSP collaborates with an Australian-based sensor manufacturer. Mike says this partnership lets WSP's instrumentation team focus on developing innovative sensor technology.
"We’re proud of how our sensor innovations are enhancing site safety and providing geotechnical engineers with up-to-date ground movement data. This project illustrates the practical application of the technology."
WSP's involvement in the project is spearheaded by a crack team of geotechnical specialists. Led by principal geotechnical engineer Shaun Grieve, the team includes geotechnical engineers Dwayne Classen and Matt Legget, project manager and site engineer Kathleen McMullan, and Kyle Gillingham and Daniel Moore, cadets in WSP's Whangārei office. Mike, Drew Yan, and Kate Chamberlin from WSP’s instrumentation team are supporting with the sensors and ground movement system.
More information about the Far North Road Resilience Programme is on Waka Kotahi's website.
