No ‘smoking gun’ at south Dublin sinkhole, engineer tells councillors

No “smoking gun” has been identified in the investigation of the Sandymount sinkhole a senior Dublin City Council engineer has told councillors.

The sinkhole more than 1 metre deep, and covering an area of 5sq m, appeared at Sandymount Green in the road in front of the Mace shop just over one week ago.

Gardaí were quick to the scene, and council workers were summoned to undertake temporary safety works after the void in the heart of the south Dublin village was exposed on Wednesday of last week.

Roy O’Connor senior engineer, with the Protection of Water Bodies Office said staff had been working since then to fill the hole in Sandymount and fully reinstate the road.

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“Initial assessment of the cause appears to be that the void was formed over a prolonged period of time, whereby the sandy soils, typically to the Sandymount area, have slowly washed into the drainage network, forming the void which eventually undermined the structural integrity of the carriageway layer above,” he told councillors on Friday.

The council’s CCTV investigators were currently at the scene to try to establish the source of the seepage he said.

“We know that the water main didn’t contribute to it; we know that the sewer may have ultimately facilitated the carrying away of sands, but that is not necessarily the cause in itself; we do have a private sewer going through there as well, which looks like it has been broken for quite a while, but the CCTV crew has now arrived on site we are trying to confirm what the actual likely cause of the event is.”

However, he said: “There is no smoking gun in this situation.”

Labour councillor Dermot Lacey commended the swift response of the council staff and other services, but said people would be worried about the potential of another sinkhole occurring.

The Sandymount sinkhole, in terms of its scale, was “a very rare occurrence” Mr O’Connor said.

“I joined the drainage department in 2002 and I’ve spoken with the various engineers involved over the last two decades, and we would have had three or four sinkholes of this kind of scale in that time, and none of them in Sandymount.”

However, he said there were “tens of thousands of kilometres” of drainage infrastructure across the city “and that is not including all the private connections to every single private property and over 55,000 gullies that all connect into our drainage infrastructure”.

Determining if and when a sinkhole would again occur would be like finding “a needle in a haystack” he said. However, he said the risk of a void the size of the Sandymount sinkhole occurring “is very low”.

The reinstatement of the road is due to be completed by Sunday. Sinkholes have appeared in recent years in Dalkey, Clontarf, Dame Street and Dublin 7.

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