WEAVER — The hole in the Chief Ladiga Trail started small five or so weeks ago, Jacksonville Parks and Recreation Department director Janis Burns said Friday.
Heavy rain earlier this week changed that.
“The guys found this Wednesday morning when they were checking the trail,” Burns said, standing a few feet from the 30-foot-wide sinkhole that has swallowed sections of the trail just north of Weaver.
There are two separate holes along the trail as it enters Weaver near Warren Drive, and Jacksonville officials Wednesday morning took to social media to warn walkers away from the section. It’s been closed “indefinitely,” caution tape and orange traffic cones posted at the section’s north and south ends.
Burns did not say Friday when she expects the trail repaired. An independent engineer who checked the sinkholes then said there’s no way to know how long it will take to fill the holes without testing the area’s soil.
“It’s the same area we’d fixed earlier, which indicates to us there could be more of a problem there,” Burns said during a phone interview Friday morning. “We’re taking extra time and precautions to make sure it’s safe for the long haul.”
The city called geotechnical engineering firm Building & Earth for help determining how deep the holes might be, and if they’re done growing.
“There’s no way to predict if that will or will not happen,” Joey Jones, a project engineer with the Birmingham-based firm, said Friday, after evaluating the sinkholes with Jacksonville’s city engineer, Mark Stephens.
Jones will return to drill for soil samples in the next two weeks, looking for the bedrock beneath and evidence that the hole won’t grow. That’s the first step in finding a fix, he said.
But drilling, depending on what’s beneath the surface, could make the problem worse, Rona Donahoe said Friday.
A professor of environmental geochemistry at the University of Alabama, Donahoe said such drilling could cause other, deeper underground caves to collapse — the likely cause of the current problem.
Limestone is the most common bedrock in which sinkholes develop, Donahoe said. Composed of soluble calcium, limestone will dissolve as rainwater percolates down through the soil’s subsurface.
As the water flows, “it follows the path of least resistance,” Donahoe said, such as fissures in the rock. Those fissures, over time, become larger and larger.
“They actually become pipes,” the professor said, and “over time, they can join to form an underground cavern.”
Depending on how water flows through the earth around the current sinkholes, she said, there could be more underground caverns in the same area.