Rideau Transit Group crews have filled a large sinkhole at the construction site where crews are digging the eastern entrance to Ottawa's light rail tunnel.

The City of Ottawa says the hole, which was eight metres wide and 12 metres deep, was filled with concrete overnight.

An exact cause has not been revealed, but the road collapse is believed to be connected to the tunnelling operation.

According to deputy city manager Nancy Schepers, the road collapsed after a digging crew in the tunnel first noticed dirt falling into the tunnel at about 10 p.m. ET Thursday.

That’s where the excavator — a roadheader called Crocodile Rouge — was gouging the earth, Schepers said during a technical briefing on Friday.

By 1 a.m., a large sinkhole had opened up on Waller Street. Nobody was injured.

Sewers still disconnected

On Saturday, workers are trying to restore power to traffic signals at the intersection of Laurier Avenue and the Transitway, and expect to complete that work by Saturday evening.

For now, police continue to direct traffic as vehicles are being rerouted and one eastbound lane of Laurier is closed between Queen Elizabeth Drive and Waller Street.

City staff said water is back at 50 Laurier Ave., but local sanitary and storm sewers won’t be reconnected until next week after workers are allowed to return underground.

Ottawa Sinkhole 20140221

The large sinkhole has halted tunnelling work on the east portal of Ottawa's LRT project. (Fred Chartrand/Canadian Press)

Crews had begun 24-hour tunnelling operations on Wednesday, but tunnelling operations remain suspended and the investigation into the road collapse continues.