Darlington project wall collapse: Construction union says photos show inadequate reinforcing

A network of lasers is monitoring any new movement in a 220m section of the crumbling Darlington roadworks retaining wall as experts begin to examine what went wrong.

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A network of lasers is monitoring any new movement in a 220m section of the crumbling Darlington roadworks retaining wall as experts begin to piece together what went wrong on the $620 million taxpayer funded project.

As soon as rains ease – predicted to be early Friday – workers will excavate dirt from two sections of the embankment which have slumped through a non-structural concrete retaining wall.

Engineers and officials at the site of the collapsed concrete along the Darlington upgrade. Picture: Tricia Watkinson

Transport Minister Stephan Knoll visited the site late Thursday afternoon for a briefing from six geotechnical engineers. He said traffic restrictions would continue, initially set at six weeks, but with no end date until the cause was identified.

Transport Minister Stephan Knoll at the Darlington roadworks site yesterday. Picture: State Government

“Again we want to apologise to motorists frustrated by the traffic restrictions,’’ he said. The upgrading work is to widen 3.3km of Main South Rd to create a non-stop motorway between the Southern Expressway and Tonsley Boulevard.

One of the team of experts briefed Mr Knoll that the laser system – designed to detect even minute movements of slopes to provide warning of large landslides – had not recorded any new movement since it was installed yesterday.

Inspections of the shape of the landslips have also revealed that the water source which pushed the slurry of dirt through the retaining wall is close to the surface.

Part of the background briefing to the State Government states: “Initial investigations suggest it is a shallow slip from the face of the retaining wall’’.

Mr Knoll said the team of experts had detailed knowledge of Adelaide’s reactive clay soils which expand and contract in wet and dry weather, but would not be drawn on whether this was a possible cause of the drama.

A photo taken during construction of the Darlington road project when the union complained about unsafe shotcrete work practices on site. Picture: CFMMEU

Photographs taken by construction workers showing a waterlogged Darlington roadworks site and unreinforced concrete being applied. Picture: CFMEU

Meanwhile, CFMMEU secretary Andrew Sutherland released photographs taken by workers which he said raised serious concerns that no reinforcing had been used in the concreting.

Mr Sutherland said that for several months workers at the site had raised concerns about the way the construction company was applying the spray-on concrete, designed as a retaining wall for the dirt embankment.

Photographs taken by construction workers showing a waterlogged Darlington roadworks site. Picture: CFMMEU

“You can tell from the way the soil has now washed out that there is no strength in the concrete, and the dirt may not have been compacted properly,’’ he said.

Three union organisers visited the site on Wednesday and are due to report their findings, Mr Sutherland said.