Posted on October 4, 2023
The geotechnical team boarded the barge before sunrise during a shift change. As they climbed aboard, the drilling crew met them with good news.
“Looks like we’re ready to drill this morning,” the crew leader said.
The news offered optimism. They might expect the first sample of the day before lunch.
The marine crew had anchored a working barge on the Ohio River 150 feet downstream from Emsworth Locks and Dams. They had been on the river 24 hours a day since the beginning of July. For the past three months, they had moved the barge to different spots every few days, both upstream and downstream of the dam and inside one of the navigation lock chambers.
“We’ve laid out 52 boring site locations. We’re drilling for structure, and those 52 borings are going to take up more than three months to complete,” said Jim James, a geotechnical engineer and team lead for the U.S. Army Corps of Engineers Pittsburgh District.
The drilling phase helps the geotechnical team collect bedrock samples to study the structure beneath the river for stability. More than 15 specialists, including geologists and civil engineers, form Pittsburgh District’s Geotechnical Section. They contribute to projects like this one throughout the district’s 26,000 square miles of land, rivers, and lakes.
“We are still in the early phase of design to gather subsurface information,” James said.
The district plans on using the data to construct a new, larger navigation chamber at Emsworth in the coming years, which will benefit commercial navigation. The construction is part of the upper Ohio Navigation Project, a multi-year plan to upgrade the three Ohio River locking facilities closest to Pittsburgh. This part of the Ohio River passes 15 to 20 million tons of materials through its lock chambers annually.
The construction would not be possible without the preliminary boring phase.
“For every dollar we spend doing this sort of investigative work in the design phase, we save probably 10 dollars or more in construction later on,” James said.
The geotechnical team measures the permeability and stiffness of the bedrock layers directly in the drilled boreholes. The team also sent samples to a lab to identify the bedrock’s strength measurements.
“If we came here to build without investigating first, we would be flying blind,” James said. “We would not know exactly what we are going to encounter. What depth, what elevations, and how much strength do these materials provide? We would be making a lot of assumptions.”
Each boring sample comes out of the ground in a 5-foot metal tube, collected by the large, yellow, metallic contraption standing on the far end of the barge. The machine looked like a miniature crane, but it was a geotechnical drill.
“This drill is a CME-55,” said Andrew Aceves, one of the geologists on the team for the Pittsburgh District. “It’s typically on land, but they park it here on the barge, chain it down, and it will sit there all summer.”
A stack of pipes lay neatly beside the machine. A two-person crew worked the drill, occasionally attaching more pipes to the drilling line to bore deeper below the water and into the rocks beneath.
On this early fall morning, the plan was to bore at least 60 feet into the bedrock. On other days, they might drill only 25 feet or so, depending on the spot. As the work progressed and the chilly morning weather turned sunny and warm, the drill ran into some problems.
The crew worked their mechanical magic to switch out pipes and drill bits, but as they hit a pile of boulders at the bottom of the river, the shifting material caused them to drill again and again in the same spot. The hole they originally formed kept filling back up with debris.
The initial excitement and hope of collecting a morning sample crumbled away. It eventually took five hours to collect the first tube, except that the first sample was mostly limestone from rip rap: a layer of rocks placed at the bottom of the river to protect the riverbed from the water’s turbulence.
“That’s not what we were looking for,” one of the geotechnical team members said.
Regardless, James said all the information they find underwater will be helpful in one way or another. Engineers could repurpose some of the sand and gravel during construction or use lab results from the silt and clay to inform their design plans.
After nearly six hours of drilling, the group broke for lunch. The marine crew leader treated everyone to a meal of enormous hoagies brought onboard. The sandwiches were nearly as long as the boring sample they had just collected.
The meal seemed to revitalize the group, despite the long hours of waiting. The job often requires a lot of patience, but Aceves expressed a personal sense of enthusiasm for the work he does.
“I know the work I’m doing is going to last, and that’s exciting,” Aceves said. “Plus, I like being outdoors. I like being on the river, or near lakes. It’s beautiful out here. It’s a great place to work.”
Finally, after lunch and more than seven hours into the morning shift, the crew hit rock bottom: a good thing. The Pittsburgh District relies on the bedrock to build the locks and dams that serve the region.
“I’ve worked on a lot of projects, building foundations, nuclear power plants and dams,” said Aceves. “The thing about dams is they’re going to last for centuries. This is something that my grandkids can come and say, ‘Hey, Grandpa Andrew worked on this thing back in the 2000s.’ It’s going to be here 200 years from now. That’s a sense of permanence.”
A white plastic tube attached to the drill sucked water out of the drill line. It spat out water that turned the color of charcoal as black debris mixed with the liquid. The sludge made it look like the drill had just tapped into an oil well.
When they pulled out the boring sample this time, it was not ashy and light grey like the last one. The black cylinder looked like the charcoal filling of an enormous pencil left exposed.
“That’s coal and shale,” James said. “That’s what we expected.”
The geotechnical team hovered over the bedrock material, taking measurements, pointing fingers at the various changes in rock material, taking notes, and selecting pieces to send to the lab. Their conversation and excitement resembled scientists discovering a new mineral, although it was an earth sample they had seen hundreds of times before.
“If there’s anything that unifies us as a team, I guess, is a sense of purpose. This is a big deal that people all over the country, even from different parts of the world, will look at the work we’re doing here,” Aceves said. “We want to do a good job, and we’re all having fun doing this.”
The team bagged the samples and stored them in a wooden crate called a “core box.” Dozens of other boxes lay stacked to the side, each filled with boring samples from the previous months of digging. The boring phase is nearly complete at Emsworth, and soon, the data collected will help engineers design the new lock chamber for construction.
“We’re cutting into that uncertainty a little bit more each time,” James said. “That’s what excites me about the work, is seeing something I’ve done – the contribution of our team – being used by other engineers going forward. It provides a level of satisfaction and pride, frankly.”