A spokesman for the developers, Geocon, said the company was unwilling to comment until it had received the engineering assessment.

Ground subsidence as a result of Canberra's recent heavy rainfall was suspected to be the cause for the spectacular collapse of a concrete wall at the site of the old Woden Tradies Club on the corner of Melrose Drive and Launceston Street.

The site is being redeveloped as Wova, described by Geocon as "a thriving residential and mixed-use community precinct". When finished, it will boast alfresco cafes, "cascading terraces" for its apartments, and a lap pool.

Geocon bought the site in 2017 for $16 million.

The side wall to the below-ground excavation site collapsed at about 2.30pm on Saturday. No-one was injured in the incident.

The 970-space, multi-storey carpark, with a Club Lime gym beneath it, is one of the largest in Woden and its closure has led to significant issues for people working in the area.

Concerns have now arisen over whether the collapse of the 15-metre high 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 adjacent carpark.

A huge deluge of rain hit Canberra on Friday and then returned intermittently throughout Saturday, coming after major falls recorded a few days earlier. WorkSafe ACT is investigating the incident and has placed a "prohibition and non-disturbance notice" on the site "until it is safe".

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The Construction, Forestry, Maritime, Mining and Energy ACT branch secretary Zachary Smith said the union also was conducting its own investigation and brushed off speculation that heavy rain had caused the collapse, saying excavations should be designed to handle weather events.

"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.

"There is obviously either a failure of design or construction or both that has led to this incident.

"It isn't good enough just to say, 'Oh, we had a bit of rain and that's resulted in this collapse'."

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