The Rideau Transit Group (RTG) has released the results of its study into why a sinkhole opened up at the site of the LRT tunnel on Waller Street on February 21.
They say the root cause was a "previously excavated construction pit" that was deeper than anyone was aware of and went below the utilities the group knew were in the area, including sewer and storm water pipes.
The pit could have dated back to projects in the 1980s when the Transitway was built. City officials don’t know and won’t be further investigating how the pit came to be filled with “poor quality, un-compacted backfill.”
Crews building the LRT unknowingly dug into that pit, bringing the tunnel and the pit together, causing the collapse.
The report confirms the crews followed all procedures, used the right tools and materials and installed the right supports as they worked.
The unexpected eight metre by eight metre metre pit was big enough to cause the sinkhole but didn't show up during tests conducted by both the city and the RTG.
Despite a massive chunk of the road opening up, RTG's technical director, Peter Lauch, insisted on Friday the project isn't losing momentum.
"We've got people with years and years and years of engineering experience, tunnel specific experience. The people doing the actual mining are well experience as well. So I really don't consider it a setback in the overall scheme."
He said tunnelling at the other two portals is slightly ahead of schedule and that the completion date remains unchanged.
Deputy City Manager Nancy Schepers pledged that taxpayers won't foot the bill.
"Essentially, in a nutshell, RTG has assumed the site conditions as is. And so anything that they encounter as part of the site conditions, they're responsible for. Pure and simple."
Lauch said he doesn't know what the final expense related to the sinkhole will be as that's still being sorted out with the consortium's insurance brokers.
Schepers said the city gave RTG the green light to resume work on that particular section after having experts that the city retains for an on call basis review the plan.