Reaching Greater Rock Coring Depths

Not even five years ago, Catawba Valley Engineering and Testing — a full-service geotechnical engineering, environmental engineering, and materials testing firm in North Carolina — bought their first 7822DT to bring all exploration in-house doing hollow stem auger and SPT drilling. As they’ve grown to 20 employees the past few years, they added another 7822DT to do work for other companies. So when they had the opportunity to do higher-level rock coring for mineral exploration in Virginia they looked to Geoprobe^® for the solution.

“We were in Salina getting training on our Geoprobe^® seismic CPT and saw the 3126GT. Once we secured the Virginia job, we thought it was a good opportunity to integrate the machine into our fleet of rigs,” David M. LeGrand Jr., P.E., owner, said. 

From purchasing their first rig in 2017 to do 15 to 20-foot SPT, to adding a second rig and doing 100-foot SPT, to integrating CPT and Geoprobe^® seismic CPT and MC5 Macro Core^® sampling, Catawba now has a larger set up for rock coring.

“We really just jumped in feet first and learned as we went. We never thought we’d be in the realm of needing a machine this size,” LeGrand said. “We were doing well with our 7822DTs and hadn’t gone down the avenue of anything bigger due to transportation and CDL regulations, but we have a driver with CDL and were able to pull together a new truck and trailer quickly to meet the Virginia project schedule."

On the exploration job looking for competent bedrock for mineral exploration purposes, LeGrand completed seven holes. In total they completed about 1500 feet of rock coring through granite/quartzite. Already LeGrand can see the advantages of the 3126GT.

“We have a 2020 7822DT set up to core confirmation rock core, but the difference between it and the 3126GT is remarkable. We wouldn’t be as deep as we are if we were running the 7822DT, it just doesn’t have quite as much juice,” LeGrand said. “We’re coring rock from 10-feet all the way down to 200-250 feet. Other than weather, we are on schedule.”

The biggest adjustment from the 7822DT to the 3126GT has been how to keep the RPMs above 700. But with the support of the Geoprobe^® service team, they identified how to utilize both hydraulic pumps after reaching 200 feet.

“Once we found the way to efficiently keep the bit running at the RPMs needed, we stayed on our goal of at least a foot every five minutes,” LeGrand said. “The coring interface shows RPMs, temperatures, and bit weight in hole versus doing it all by feel, providing visual indicators to show we’re doing as much with the machine as we can without forcing things downhole.”

The centerline head side shift and outriggers have also aided their efficiency.

“Shifting back and forth between different downhole tools, especially not swinging the auto drop hammer over, has been a huge time saver,” LeGrand said. “Our productivity has increased with the larger machine, larger winch, and ability to pull more rod directly out of the ground with the taller mast."

Because this client does a lot of mineral exploration, they anticipate being able to send the 3126GT to Virginia to work while still keeping up with the quantity of work in North Carolina by having their two 7822DTs running conventional SPT and CPT work.

“I was going to sell the second 7822DT, but business has been good enough and consistent enough that we are going to keep a fleet of three machines,” LeGrand said.

Based on the level of service and the performance of the machines, LeGrand doesn’t anticipate changing rig manufacturers.

“I’ve only ever run Geoprobe^®, but talking to guys I learned to drill from, the service is outstanding compared to other manufacturers. Every time we call up, if they don’t have the answer, they do in a short time. I can call a service technician who knows what they’re talking about to troubleshoot issues in the field,” LeGrand said. “The relationship is worth just as much as the machine performance to me.”