The city signed off on deep excavation plans for the Brooklyn construction site being eyed as the potential cause of this week’s deadly building collapse — even though it lacked key structural support, The Post has learned.

The Department of Buildings approved the allegedly shoddy plans in March for the excavation of the lot at 2625 Bedford Ave, where a developer was set to build a three-floor, 25,000-square-foot mixed-use building.

Records show the plans provided extensive and sophisticated shoring and bracing along the majority of the lot, including the backyard of 1321 Flatbush Ave. — the adjacent building that suddenly partially crumbled Wednesday, killing eight people and injuring nearly 20.

But the plans crucially did not include any hard reinforcements right alongside the now-collapsed building, according to records and experts.

Even a study submitted by contractor Townhouse Buildings in support of the excavation permit application noted that structural reinforcement would be necessary to shore up 1321 Flatbush Ave.

The geotechnical report from November 2025 explicitly noted that the three-story apartment building “would need underpinning” — a pricey process where a neighboring foundation is extended and reinforced from below to prevent it from collapsing during excavation.

According to the city-approved plans, that never happened.

Experts were shocked by the substandard plans — and the city greenlighting them.

Architect William Gati, a longtime professor of architecture at the New York Institute of Technology, said he and his team “would never in a million years have done it that way.”

“I would have absolutely underpinned the building,” said Gati, after reviewing the site’s filings. “I would have adhered closely to the geotechnical report.”

Another veteran architect, who asked for anonymity because they currently work for the city, called the plan “irresponsible,” and said it might even rise to “intentional incompetence.”

Rick Chandler, a former city DOB commissioner and engineer, said the approved plans sparked more questions about the tragic collapse.

“The geotechnical report made references to and assumed underpinning for adjacent buildings,” said Chandler, “but that the corresponding excavation plans don’t appear to show any underpinning.

“They only show the bracing of all the remaining portions of the lot, but it doesn’t even show bracing at the subject building at the collapsed building location,” he said.

New Jersey-based engineer Jieming Wang, who submitted the plans for approval earlier this year, did not respond to a list of questions, nor did the DOB.

The DOB approved another excavation permit for the site as recently as September, and the work was taking place there around 4 p.m. Wednesday when the adjoining apartment building crumbled into the lot.

Well before that, Townhouse Builders — owned by Mordchai Waisbrod — paid for the required geotechnical study of the soil at 2625 Bedford Ave.

Those investigations are required to find facts about the ground, including if the soil can support the proposed building, how deep the groundwater is, and how to prevent surrounding structures from collapsing when a giant pit is dug.

The resulting Nov. 21, 2025, geotechnical report originally assessed for a 10-story building, and revealed the site rested “over a geological deposit of beach and dune sands” that was “not well compacted” until 42 feet.

Additionally, the building aimed to dig about twice as deep as 1321 Flatbush Ave.’s foundation, listed as less than eight feet below the sidewalk.

Plus, like many old Brooklyn buildings, the foundation rested atop a “rubble” foundation wall, according to DOB filings.

“It is expected that the adjoining buildings abutting the lot line would need underpinning,” the report explicitly says — with the only question being how extensive the support work should be. 

More coverage on the deadly Brooklyn building collapse:

But when the plans were filed months later, underpinning was left off the table entirely.  

Instead of extending the neighboring building’s foundation down with concrete piers to prevent the soil from rushing out, the approved plans relied on benching, or an unbraced, stepped dirt slope.

Benching may have been risky in this project given the sandy soil composition and the plans to dig four feet below the “rubble” wall, experts said.

Still, DOB plan examiner Shahinaz Moubarek approved the plans on March 22, records show.

Gati, the veteran architect, said the idea that the project could avoid underpinning went against basic physics.

“If you have a rubble foundation, you don’t use a step footing,” he said. “What’s the point of a geotechnical report if you’re not going to follow it?”

Former DOB boss Chandler said the diagram for the benching appeared to be missing dimensions or slope ratios that typically are required on plans.

“Which seems at odds with the remainder of the drawing because those details seem to be fairly explicit, but they don’t seem to be explicit underneath this building,” he said. 

The developers sent in new plans for a larger, nine-story building with 64 low-income housing units, plus grocery and ambulatory services on the ground floor, in September, but the DOB never signed off.

DOB Commissioner Ahmed Tigani confirmed Friday that the builders were not digging for a larger, nine-story building.

The DOB is investigating the cause of the collapse, and Mayor Zohran Mamdani on Thursday also ordered a review of more than 100 other sites across the city linked to five entities involved in the construction.