ACT WorkSafe has closed a lane and footpath on Eastern Valley Way after Engineers Australia raised the potential for a more serious collapse than the partial subsiding over the weekend.
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WorkSafe had already stopped work near the wall on the site of an $80 million units project on the corner of College Street and Eastern Valley Way, Belconnen.
A photograph on canberratimes.com.au of a workman at the base of the excavation alarmed Engineers Australia.
Canberra division president Andrew Montgomery spotted the danger immediately, because the freshly cut wall is unprotected.
The photo was taken before the two-storey embankment collapsed.
Based on a diagram from a work health and safety code of practice, Mr Montgomery's diagram shows the ''zone of influence'' of the excavation extends under the road, which is used by heavy trucks as well as cars.
''That whole section, the dotted line at 45 degrees and red lines 1 to 1, (representing a one-to-one slope in the diagram), that slab can cave in.''
After ACT WorkSafe commissioner Mark McCabe spoke with Mr Montgomery on Tuesday afternoon he arranged with Roads ACT to close Eastern Valley Way between College Street and Cameron Avenue as an immediate precaution while more investigations take place.
Mr McCabe could not say how long the road would be partially closed.
Mr Montgomery said the collapse and ones like it were caused by not having a project specific design by professional engineers.
Professional engineers should also inspect all critical aspects of construction and certification.
Mr Montgomery said the photograph of the wall showed grey shotcrete on the left and right to stabilise ground.
But if not reinforced, all it would do was stabilise very loose pieces of earth.
''If this [wall] is clay, which I suspect, those walls of shotcrete would have to act as a structural member, that means there would need to be serious reinforcing in that concrete to make it act as a retaining wall.''
Mr Montgomery said the Construction, Forestry, Mining and Energy Union was right to warn of the danger.
''As a matter or urgency that footpath and that part of the road should be blocked off and that wall stabilised, or an investigation carried out by a competent person to make sure it is okay.''
