What lies beneath

What lies beneath

Looking below the surface of existing roads is important to avoid nasty surprises. Not only can construction projects unearth things that nobody expected to find, the delays can be costly.

That is according to Wayne Muller from radar company Earth Radar who says it is important that contractors are not guessing when it comes to building infrastructure projects.

“Details of existing roads may be incorrect, outdated or missing. This can lead to confusion during road upgrades regarding what is actually present,” Dr. Muller says.

“Digging a hole gives you an answer at one location, but is it representative of a longer length of road? If so, where is it representative to and from? Where should you dig trenches or cores for the greatest benefit? If it’s a busy road, traffic control can cost a lot and so it pays to target these investigations to the most representative locations,” he adds.

To handle that problem, Earth Radar developed Sparas – a trailer-mounted data collection system that incorporates 3D ground-penetrating radar (GPR) technology, which can detect and measure road subsurface details.

Dr. Muller says Earth Radar, as part of the VAC Group, specialises in the development of next-generation GPR technology.

He says being able to gather this information at highway speeds not only increases efficiency but also makes the roads safer.

“There’s little to no public disruption with this technology as we can move along with the traffic. As a result, expensive traffic control isn’t needed. We’re also able to cover most of the lane in one pass instead of many,” Dr. Muller says.

“By keeping up with traffic, we remove the need to inconvenience motorists with traffic control. It also lets us collect measurements across the road network and view them later, providing details of what’s within the road without having to travel to each site and dig holes.”

Innovative radar technology, combined with many antennas that remain near the road surface, is what lets Earth Radar achieve a high degree of measurement quality.

“We’ve designed the antennas within ‘pods’ that hug the road surface. This lets them get very close to the ground to get a better scan. Each pod normally works like a cart, but they can move out of the way if they hit ruts or bumps along the road. Shock absorbers make sure the pods don’t bounce and that they quickly return back to their correct positions,” Dr. Muller explains.

He adds that by collecting measurements close to the ground, the technology is able to see greater detail and penetrate to greater depths.

Over the past 10 years this radar technology has been used to scan more than 10,000 lane-kilometres of Australian roads. The measurements are then georeferenced using real time kinematic GPS positioning. GPR technology has been around for many years, but Dr. Muller says Earth Radar’s system uses a unique approach. Coded radar design lets Earth Radar capture 30 slices across the road covering a 2.4-metre width in a single pass. They can then use these measurements to see many different things below the road surface, including pavement layer boundaries, buried utilities and voids.

“To test the limits of the system, we ran a trial to see if we could distinguish individual reinforcing bars within a concrete bridge deck using 3D GPR measurements collected at highway-speeds, and we could,” he says.

The technology allows companies to survey the ground and find both metallic and non-metallic objects. “It’s important to find any nasty buried surprises early in the construction timeline, instead of on the day you start excavating. At that point you might have the wrong equipment on site and it becomes very expensive to change the design. Many of these problems could have been avoided or fixed if engineers had this additional information before completing their designs,” Dr. Muller says.

GPR is often used for investigating road or airport pavements and for locating buried utilities. It’s also useful for finding hidden defects within the road or infrastructure that was just buried instead of removed. It can all become very expensive and cause delays if you don’t know what’s underneath your project site, Dr. Muller says.

“If you can identify these potential problems early, changes can be included in the design leading to fewer project disruptions and blowouts of time and cost.

“The technology is also useful for detecting moisture infiltration to help with road upkeep. You can use GPR to locate where water is getting in, which is useful for targeting maintenance to the right areas and for ensuring we are applying the most appropriate treatments.

“There is an old saying about road maintenance, that there are three main things that wreck roads: Water, water and water. GPR gives us a non-invasive way of finding out where water is getting in, to help work out the location and size of any problems.”

A smaller push cart system, called Latro, is also available and is designed for utility locating. It is a more agile device and is most often used on footpaths, parking lots and open fields.

Dr. Muller says the names of the Sparas and Latro are shortened versions of the scientific name for Australian spiders, giving these home-grown machines a unique Aussie spin.