PLYMOUTH – A pile of rubble stands on Route 7 where the Maine Department of Transportation’s salt and sand shed stood near the Interstate 95 exit at Plymouth. One week ago, the 13-year-old dome-shaped building came tumbling down, apparently without any witnesses.

On Wednesday, crews were working to lift the debris and remove a 1989 dump truck from the interior.

According to Jerry Hathaway, MDOT Supervisor at Plymouth, the building was intact when workers left work last Thursday at about 3:30 p.m. When the night patrol checked in around 10 p.m., the roof was caved in.

“We’d been watching it every year, taking survey shots of the settlement,” Brian Pickard, MDOT highway maintenance engineer in Augusta, said. “It just came down sooner than we expected.”

The Plymouth building is the second dome-shaped shed to collapse under the weight of snow, Pickard said. In 1993, the largest MDOT dome in the state collapsed in West Enfield.

Pickard explained the buildings are designed for weight to be evenly distributed, but a miscalculation between the foundation base and walls allowed the structures to settle more than anticipated. Settling into the foundation causes the building to tip and put the weight distribution off balance.

“There may have been five feet of snow on the back side of that roof,” Pickard said of his observations at the Plymouth collapse. “It caused a disproportionate load on that side.”

The state no longer uses the dome design for salt and sand sheds, he said. The original structure cost $150,000 to construct, but could cost $300,000 to replace with the new Quonset-style design. The Quonset building is made of corrugated metal over laminated arches.

The new design causes virtually unlimited capacity, Pickard said.

“You just make the building longer,” he said.

The Plymouth building was insured for $135,000 under the state’s self-insured risk management plan. Pickard expected the building might be replaced before next winter, but he was not sure if funding was available for the balance of the project.