Construction company Grocon has been ordered to pay $250,000 after a wall on its building site in Melbourne collapsed killing three people last year.

French academic Marie-Faith Fiawoo, 33, and siblings Bridget and Alexander Jones, aged 18 and 19, died in March 2013 when the large brick wall blew over in strong winds at the site in Carlton.

Grocon had pleaded guilty to a single breach of a workplace safety law last week and expressed "deep regret" over the deaths.

In sentencing, Magistrate Charlie Rozencwajg said there was an extremely large number of people put at risk of serious injury or death.

He said the incident represented a significant failure of the company's duty, but acknowledged Grocon had since acted in the manner expected of a good corporate citizen.

Grocon was developing the site and was charged by the Victorian WorkCover Authority, along with sign company Aussie Signs.

The wall in Swanston Street had a large awning fixed on it.

Earlier an expert witness told the court that the wall would only be safe for five to 10 years without the hording attached, and only six to 12 months with the hording attached.

It heard the witness stated the wall was supposed to have been safe for 500 years.

The site in Carlton was formerly owned by Carlton and United Breweries before that company sold it to tertiary institution RMIT in 1998.

Union condemns 'slap on the wrist' fine

Daniel Grollo, the executive chairman of Grocon, said his thoughts and sympathies remained with those affected by the deaths.

"I personally, along with all of the directors and employees of Grocon, reiterate our deep regret at the tragic and untimely loss of Bridget and Alexander Jones and Marie-Faith Faiwoo," he said.

"In whatever small way, we hope that the timely conclusion of the proceedings today assists the families and friends affected by this tragedy."

But in a statement, the Construction, Forestry, Mining and Energy Union (CFMEU) said the fine was "no more than a slap on the wrist" for a company with "an appalling safety record".

John Setka, the state secretary of the CFMEU and who was one of the first people on the scene, said the incident was a "shocking reminder" of the need to fight for safety in the construction industry.

"Our industrial dispute with Grocon has always been about safety," he said.

"The union was recently fined $1.25 million for protesting against Grocon's safety record.

"That company has been fined a fraction of that after being convicted of a crime which contributed to the deaths of three innocent people."