While the engineering analysis continues, property developer Geocon is not prepared to offer any comment as to the possible cause of the collapse, which occurred around 2.30pm on Saturday.

Work had stopped at the pit on Saturday after two days of rain, and fortunately no-one was injured in the incident.

WorkSafe ACT has slapped prohibition and non-disturbance notices on the site, with no access permitted. Several excavators sit idle at the base of the pit.

Hundreds of tonnes of earth and concrete, together with steel scaffolding and fencing, have cascaded into the deep excavation on the corner of Launceston Street and Melrose Drive.

The huge ground shear took out a large section of concrete roadway which was the vehicle exit road onto Melrose Drive for the seven-storey Sky Park carpark next door.

The excavation, which is some 20 metres deep, was for the multi-storey underground carpark which will underpin Geocon's massive new mullti-million four-tower WOVA residential and commercial development.

The site is that once held by the former Woden Tradies Club. The site was bought by Geocon in 2017 for $16 million.

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Concerns have now arisen over whether the collapse of the retaining wall, which had been held in place by reinforced steel piers encased in concrete and sprayed concrete render, now has implications for the structural rigidity of the privately owned car park, which remains closed.

WOVA is planned to have a "signature" 24-storey tower on Launceston Street, a 16-storey building behind it fronting Furzer Street, and two separate 12-storey buildings adjacent.

Facilities planned for the site include a cinema, gym, lap pool and spa, dining area, co-working area, yoga room, bar and lounge, and golf simulator. A sky bridge will connect two of the buildings.

A 63-room Abode hotel is planned to occupy the first and second floors of building 1.

WOVA will have 797 apartments and 967 car parking spaces.

The Woden wall collapse is one of four incidents which have affected construction sites owned by Geocon, a prolific Canberra property developer, in the past six years.

In 2016, a collapse occurred during the excavation for the Southport apartments in Tuggeranong, in 2018 prefabricated concrete panels inside a lift shaft collapsed and fell seven metres down the shaft during the construction of Geocon's Midnight apartments in Braddon, and in 2019 part of deck form collapsed at Republic, in Belconnen.

All incidents sparked WorkSafe ACT investigations.

WorkSafe ACT was unable to be reached on Tuesday for an update but Construction, Forestry, Maritime, Mining and Energy ACT branch secretary Zachary Smith has expressed his concern at this latest incident and says the union will conduct its own investigation.

"This is a very serious incident, if there had been workers working that on excavation, if it'd been a normal business day or occurred during business hours, we could be easily looking at multiple fatalities," Mr Smith said.

"These excavations should be and are in the normal course of business designed and constructed in such a way as to withhold what is a fairly normal weather event. Sixty millimetres of rain is not an extreme or freak weather event by any stretch of the imagination."

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