The collapse of an I-295 retaining wall under construction in Bellmawr was caused by a partial collapse of a below ground support system after heavy rains, state DOT officials said in a letter to District 5 legislators who’ve been pressing for answers about the March incident.
The retaining wall is part of the larger $900 million Direct Connection project to ease traffic congestion and reduce crashes at the junction of I-295, I-76 and Route 42 in areas of Bellmawr, Mount Ephraim and Gloucester City. The massive project has been under construction in phases since 2014. The wall partially collapsed sometime between the evening of March 24 and early March 25 of this year.
“After requesting an update on the NJDOT’s forensic investigation into the Direct Connect project’s retaining wall collapse, Commissioner (Diane) Gutierrez-Scaccetti provided me with a synopsis of their preliminary findings,” said Assemblyman William F. Moen Jr., D-Camden. “We are now aware of several possible contributing factors, and have been assured by the Commissioner that the public will be informed of any new information as it becomes available.”
Moen and District 5 legislators pressed the DOT for answers, and Gutierrez-Scaccetti lead an April 7 virtual hearing about the incident.
The additional information was detailed in a Sept. 15 letter from the commissioner to the lawmakers that was obtained by NJ Advance Media.
The letter revealed findings made so far by engineering firm Hardesty and Hanover, hired by the DOT last spring for $282,000 to conduct a forensic engineering investigation into the collapse. NJDOT is also investigating the cause of the collapse of the structure, known as Wall 22, with its contractors, designers, consultants and in-house staff.
As part of the forensic investigation, H&H has been deconstructing the wall, the letter said. They found that there was a partial collapse of a column-supported embankment system.
That system uses columns or piles spaced close to together to provide additional support when soils are deemed too soft to support an embankment or road.
“It appears Wall 22′s collapse involved both vertical and lateral displacements of the embankment fill materials and showed the partial collapse extended through the Column Supported Embankment System,” the DOT letter said.
The letter also said a high ground water condition and heavy precipitation on March 24 exacerbated the condition, “affecting the embankment material and the column supported embankment system. The high ground water condition appears to have compromised the subsurface soil conditions.”
In July, an NJDOT spokesman told NJ Advance Media that that excessive groundwater played a part in the collapse of the Wall 22.
In such situations, the excess groundwater weakens the soil to the point where it can’t carry the load placed on it, said Professor Nenad Gucuniski, Rutgers University civil and environmental engineering department chairman, in July, when NJ Advance Media asked him to examine photos of the collapsed wall.
“Once the soil is saturated, that water pressure reduces the frictional resistance and it (the soil) loses strength,” he said. “That leads to soil weakening.”
Officials were alerted about two years before the incident by U.S. Rep. Donald Norcross, D-NJ, that some of the retaining wall tiles started to bulge, Gutierrez-Scaccetti said in April. That was because water got behind the wall, froze and pushed out walls, an issue that was addressed with the DOT’s project contractor, she said.
The Sept. 15 letter cautions that until the forensic investigation has been finalized, “definitive causes of the partial wall collapse can’t be ascertained.”
Failures of other similarly-constructed retaining walls have occurred in other states. Most recently, a Route 7 pedestrian bridge was closed in May 2020 after a retaining wall leading to the Duck River bridge in Marietta, Ohio collapsed in a similar fashion to Wall 22.
Officials blamed a “land slip” behind that retaining wall that bucked parts of the wall and ripped apart asphalt on the pedestrian walkway. That wall has not been repaired a year later, according to the Marietta Times.
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Larry Higgs may be reached at lhiggs@njadvancemedia.com.
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I-295 wall collapsed after heavy rains undermined supports, initial probe reveals - NJ.com
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