A recent Tennessee Department of Transportation (TDOT) study discovered that it was a 37-year-old retaining wall that failed, not the overpass bridge, on the 28th Avenue exit ramp at I-40, west of downtown Nashville.
There were no injuries and no vehicles were damaged when the 25-ft. high wall collapsed suddenly on Sept. 10, just before 11 a.m.
“It is important to remember that it was a retaining wall that failed, not a bridge. The adjoining bridge was inspected immediately and is structurally sound,” TDOT Commissioner Gerald Nicely said.
Referring to a three-page, detailed report drafted by the department’s engineers, Nicely outlined the reasons for the wall failure at a recent news conference.
“Our engineers have determined that there was a gap or void at the bottom of the wall where it attached to the footing. That gap, or defect, allowed water to seep in and cause the corrosion of the steel reinforcing bars,” he said.
Bill Moore, TDOT’s chief engineer, said that the defect in the wall’s base occurred when the concrete was poured. “We have determined that there was not a proper seal between the wall and the footing. There were also signs of other debris interfering with that initial seal, including mud and gravel.”
Moore went on to say that such a defect is difficult to detect. “We did see a slight amount of movement to the wall in our last inspection in October 2001. Such movement of a concrete wall is expected over time and didn’t warrant any immediate attention.”
TDOT has 112 inspectors in the field who are responsible for inspecting the nearly 19,500 bridges in Tennessee. There are 31 inspectors in middle Tennessee. All bridges are inspected every two years.
Prompted by the collapse of the 28th Avenue bridge, a state review of more than 485 walls adjoining bridges and overpasses showed that 11 other bridges need attention.
Inspectors determined that nine structures owned and operated by the state and two others require further investigation.
TDOT spokeswoman Kim Keelor said no problems were found with the bridges that adjoin the “bridge wing-walls.”
The 11 locations identified by the state are:
• Davidson County, James Avenue-Briley Parkway;
• Greeneville, Railroad Street-State Route 350;
• Henry County, State Route 76-East Blythe Street;
• Hickman County, State Route 48-Piney Fork Creek;
• Johnson City, Forge Road-Forge Creek;
• Knox County, Western Avenue-Interstate 40 and East Fifth Avenue-Interstate 40 westbound;
• Lincoln County, State Route 50-Pamplins Branch;
• Montgomery County, State Route 13-East Fork Creek;
• Roane County, State Route 61-Caney Creek;
• and Shelby County, Interstate 240 westbound exit ramp-Interstate 20.
“The follow-up investigations or the nine state-maintained structures is currently under way and will completed within 90 days,” said Keelor. “The bridge team will make recommendations on work needed to reinforce those walls at that time.”
She said that while a “small amount of movement can be expected over time, all wall distortions are now being investigated more intently since the recent wall failure.”
Keelor said TDOT was working to identify the original contractors. She said the work was done by a variety of contractors and there is “no pattern there, to our understanding.” She said the walls were built between 1936 and 1980 and many of the contractors have since gone out of business.
“For some of the earliest, we don’t even have blueprints for designs,” Keelor said.
She said any repairs would involve reinforcing the walls.
The wall problems are another sign that “our roads and bridges are aging. We are going to have lots of bridge repairs needed in the near future,” she said.
Nine percent of Tennessee’s bridges are structurally deficient – tying it with six other states for the 11th best among the 50 states, according to the Road Information Program, a Washington D.C.-based nonprofit organization that studies transportation issues.
(Information from the Associated Press is included in this article.)