The recent collapse of a wall along an unfinished stretch of I-75 has prompted more extensive repairs and could delay the opening of 30 miles of toll lanes in Cobb and Cherokee counties, documents exclusively obtained by The Atlanta Journal-Constitution show.
An engineer’s report shows design and installation problems likely led to the collapse of the wall along the lanes near Windy Hill Road in June. But the problem may not be limited to the section that collapsed, and workers must now fix other walls along the Northwest Corridor Express Lanes.
The report also found the recent incident wasn’t the first sign of trouble. Another section of the same wall collapsed in July 2017, but that incident did not prompt a full investigation.
Construction workers look over a section of the Northwest Corridor Express Lanes project on Interstate 75 South close to Windy Hill Road, near where a wall collapsed recently in Cobb County. Curtis Comptonfirstname.lastname@example.org
Photo: The Atlanta Journal-Constitution
The Georgia Department of Transportation did take steps to address the problem last year. But the full extent of the problem was not discovered until this year’s collapse prompted the agency and the project’s general contractor to seek an independent engineering firm to determine the cause of the wall collapse.
It’s unclear how long the repairs will take and when the new lanes will open. GDOT spokeswoman Natalie Dale said that if the lanes open by the end of September the project would still be on schedule.
However, GDOT could offer no timetable for completion of the $834 million project Monday. The agency had been planning to open the lanes by the end of August.
Dale said wall repairs aren’t the only factor in the schedule. Paving, striping, equipment testing and safety training all must be finished before the lanes open to the public.
“We won’t open the system until there is a safe and complete system for motorists, so the opening may be in the fall,” Dale said. “We have not yet set a groundbreaking date.”
A delay would be bad news for motorists seeking relief on a stretch of highway traveled by more than 300,000 vehicles a day.
When they open, the Northwest Corridor Express Lanes will allow motorists to drive along at speeds of 45 mph or more – if they’re willing to pay a toll of 10 cents to 90 cents a mile. They’re part of a planned 120-mile network of toll lanes – some of them already open – that GDOT says will help ease metro Atlanta’s awful traffic.
Construction of the Northwest Corridor has been hindered before. Last year’s collapse of I-85 in Buckhead prompted a halt to construction on I-75 as state officials sought to manage the resulting traffic nightmare. GDOT estimated that set back construction of the new I-75 lanes by up to six weeks.
‘The failure was localized’
Then in June, a section of wall collapsed near Windy Hill Road. The lanes are not yet open to traffic, and no one was injured in the incident.
The wall that collapsed was a facade wall in front of a sturdier retaining wall. The walls are connected by a series of large “soil nails” – reinforcing bars driven through the walls and into the soil. The crushed stone used as fill between the walls spilled out onto the unfinished lanes when the facade wall collapsed.
Afterward, general contractor Northwest Express Roadbuilders asked the engineering firm Wiss, Janney, Elstner Associates (WJE) to investigate.
WJE’s July 26 report, obtained by the AJC through an Open Records Act request, concluded that the primary cause of the collapse was the inadequate design of the system connecting the facade wall to the retaining wall. Installation of tie rods at excessive angles also may have contributed, the report found.
Ken Golski, corporate counsel for the company that designed the wall, Reinforced Earth Company, said other reviews of this year’s incident are ongoing and point to other causes. He said he could not elaborate.
“I feel very confident in our product and in our design,” Golski said.
The general contractor, Northwest Express Roadbuilders, could not immediately be reached for comment.
According to the WSB 24-hour Traffic Center, a wall collapsed along an unfinished portion of the Northwest Corridor Express Lanes project.
Photo: Channel 2 Action News
WJE’s report also disclosed the previous incident from 2017, when a section of the same wall collapsed. Although “a full forensic investigation” was not done, a “non-conformance review” found evidence similar to those discovered after this year’s incident, the report found. Those included fractured or bent soil nails.
Last year’s incident prompted GDOT to suspend work on the walls. It increased inspection of walls built afterward, the report found. But the portion of wall that collapsed this year had already been built.
In written responses to AJC questions, GDOT said the agency and Northwest Express Roadbuilders also inspected the wall sections that had already been built. It said the contractor “concluded the failure was localized, and a repair procedure was recommended and implemented” by the contractor.
“The assessment recommended increased inspection for the remaining similar walls, which GDOT had no reason to believe was not the appropriate action at that time,” GDOT said.
The agency noted that “over 85 percent of the soil nail walls were completed without incident when the first failure occurred in July 2017,” including the section that failed this year.
Now that the problem has been discovered, WJE recommended retrofitting similarly constructed retaining walls along the Northwest Corridor with new soil nails to sufficiently anchor the facade wall.
GDOT said only 14 of the 69 retaining walls along the 30-mile corridor are similar to the wall that collapsed – about 1.75 miles of walls. Northwest Express Roadbuilders has told GDOT it will complete the repairs later this month.
The agency said that – under the terms of its contract – it’s the contractor’s responsibility to repair the walls and bear the cost.
It’s too soon to tell whether GDOT will penalize Northwest Express Roadbuilders or Reinforced Earth Company, officials said.
“GDOT reserves the right to ensure all concerns are addressed and the project is being delivered appropriately,” it said.