Seeing What Can’t Be Seen
Concrete GPR’s use of subsurface imaging provides quality, state-of-the-art solutions
When Jeff Sohlstrom and Reid Davis left their jobs working for a ground-penetrating radar provider, neither had any intention of starting their own company. “We were both unemployed, but wanted to figure out how to make a living doing what we are good at,” says Sohlstrom, Co-Owner of Concrete GPR LLC in Albany, Oregon. “At the time, we had nearly two decades of combined technical experience with ground-penetrating radar (GPR) scanning. As we were exploring employment options, the idea of starting our own company kept surfacing. Even though neither of us had any prior experience running a company, we raised enough capital and decided to make a go of it.”
Davis and Sohlstrom shared the same vision when creating their company: Focus on the customer first. “We felt there was a void among high-level GPR providers that were committed to delivering quality customer service,” says Davis, also a Co-Owner. “Our goal is to make sure clients are getting the best care possible for their needs, both in the field as well as in any follow-up service.”
It’s a tenet that has served them well. Since its founding in 2016, Concrete GPR has become a leading specialist in providing nondestructive concrete and underground imaging services using GPR.
“After [more than] three years in business, the company is well established, and our brand is well built in the area,” Davis says. “Of the highest-profile projects in Portland, Oregon, Concrete GPR is active on at least half of them. And while most of our clients are in the Pacific Northwest, we will travel nationwide or internationally, on demand. We’ve done projects as close as the Midwest and as far away as the Middle East.”
Measure Twice, Cut Once
The biggest market that Concrete GPR serves is the concrete world. “Clients hire us to image reinforced concrete to locate steel rebar, post-tension or pre-stressed cables, or electrical conduits,” Sohlstrom explains. Using two-dimensional (2D) line scans, field technicians can analyze a project by interpreting the reflection files from a GPR unit and mark the findings directly onto the concrete in real time as a scan is underway. “Pinpointing the exact locations of cables or conduits helps companies keep their employees safe before they start to drill,” he adds.
But 2D line scans aren’t always appropriate for every project. In those instances, the company offers its advanced three-dimensional (3D) grid-scanning service because it produces better data quality and it can overcome obstructed site access. These 3D grid scans also provide permanent documentation for insurance and inspection purposes.
“With a 3D grid scan, we can create a high-density grid of ground-penetrating radar data that gets processed back in our office,” Davis says. “This allows us to evaluate a project in precise detail. Because we’re working with a 3D data model, we report our findings in detailed reports.”
Concrete GPR is equally adept when performing underground imaging. “We are highly experienced in scanning a wide range of underground conditions, including utilities, storage tanks, voids, sinkholes and tree roots,” Sohlstrom says. “When building a new structure or renovating an old building, there are numerous subsurface hazards that need to be accounted for prior to excavation, core drilling or saw cutting.”
Although not as commonly requested, GPR is also useful in archaeological investigations, including finding unmarked graves or time capsules. “After an area has been dug and backfilled, the edges and fill material are identifiable against the native layering for many years,” Sohlstrom explains. “Our staff has years of experience discerning human-impacted areas of the ground from naturally occurring artifacts.”
Scanning for Success
Rising on the west bank of the Willamette River in Portland is the new 17-story Multnomah County Central Courthouse. The 461,000-square-foot building features 44 courtrooms and replaces the original Multnomah County courthouse that was built between 1909 and 1914. The new building is scheduled for completion this fall. It is considered a flagship project for the region and is one of Concrete GPR’s largest projects to date.
“Hoffman Construction Company, the general contractor, reached out to us in August 2018 after the first seven floors had been poured,” Davis explains. “We provided the highly accurate results that Hoffman needed for a project of this magnitude, and we’ve been on the job ever since.”
Concrete GPR has provided 2D scanning on every level of the building, including the roof, and the team has worked for many of the subcontractors involved on the project. “There have been times when we’ve been alongside the workers putting on exterior stone or with crews installing clips to hold the giant windows,” Davis says. “We’ve also worked for the subcontractor installing the electronics inside the holding cells, as well as the masonry contractor. And we’ve worked with the project engineers to help fine-tune slab edges in tight tolerances.”
Davis went on to explain that it’s not uncommon for changes to be made while new construction is underway. Human error, field conditions and design changes can all result in the need for adjustments after concrete has cured. Project schedules can be so aggressive that design and engineering need to happen in real time, concurrent with construction. In these instances, GPR is a proactive application that can prevent costly delays or change orders.
“When we’re on-site scanning, we leave our findings directly on the surface,” Davis says. “The engineer can walk up to the drawings on the concrete, see exactly what’s going on underneath and make any necessary adjustments. 2D scans allow the work to proceed as soon as possible.”
Another project that highlights Concrete GPR’s capabilities is an expansion that will more than double the size of an existing campus for a major sportswear manufacturer. Construction began in 2018 on three new buildings, including two three-story buildings and a five-story structure, totaling 425,000 square feet.
“The five-story structure is being built on top of an existing parking garage that wasn’t originally designed to have a building on it,” Sohlstrom says. “The engineers needed to strengthen the shear walls and enlarge 13 existing columns from 2 feet in diameter to 4 feet to allow the weight of the new building to transfer into the ground.”
Sohlstrom further explained that each of the columns needed six cores to allow rebar to pass through the levels. “Columns have a lot of cable running in multiple directions,” he adds. “It’s a very tight and technical procedure to safely drill the holes. The project also involved cutting a new elevator shaft through the roof of the parking structure. In some instances, we were laying out safe drill holes where there was only a one-quarter to one-eighth-inch tolerance.”
“Early in the project, general contractor Turner Construction Company brought out traditional X-ray technology from another service provider and contrasted our findings with theirs,” Davis says. “They put both of us in the same locations and compared the quality and reliability of the findings, as well as the cost benefit. A lot of people have a misconception that X-ray can see everything, but in a head-to-head matchup, Concrete GPR won out. We’re really proud of that fact.”