River Dargle Flood Defence Scheme.
These images were taken during the third week of November 2016.
These are the critical stabilisation works at the Silverbridge site, adjacent to the N11 dual-carriageway:
Back in November 2014, we observed bank stabilisation works here involving excavation, repair and building of a support wall structure — carried out by JONS Construction on behalf of the National Roads Authority.
We would occasionally catch sight of this work in the distance. Quite an impressive little piece of structural engineering.
Having built a retaining concave wall, backfilled for solidity, they were also drilling, fixing and sealing ground anchors to pin the entire structure together.
Now we see that further works are being undertaken.
Word has it that extra ‘stabilisation work’ has to be done to protect the integrity of the riverbank. At the section here we can see that there’s not much space between the edge of the rock face and the Armco at the side of the dual-carriageway.
Have yet to determine what precisely that will entail. Serious work to reinforce the side access ramp down to the river.
The N11 carriageway runs adjacent to this sunken side of the riverbank — barely 2 (large) paces divide the two. Even with twin strips of Armco along the roadside, it’s perilously close. Traffic speeds along this stretch (maximum speed 100 kmp). Only needs a touch from a heavy vehicle to cause secondary impact, which (worst possible scenario) could result in something going airborne.
Working in these confined spaces puts a premium of safety and communication.
The guys have hard-filled a working shelf on the riverbed, to allow machinery access to the rockface. Obviously some serious drilling is called for before a form of extra ‘pinning’ is put in place.
They have sunk a series of hollowed tubes/casings — obviously to form the foundations of a more extensive structure.
And some investigative work around the transverse buttress of the access bridge, parallel to the heavy-duty pipeline carrying water down from the Vartry reservoir.
At a (rough) guess — I’d say the foundations are sunk to a depth of approx 4+m.
With such secure foundations in place, they would then look to construct a substantial bank of material, and/or retaining wall (similar to that in place further along the roadside bank).
Work continues on filling the sunken foundation casings with liquid concrete solution.
They have abandoned the use of the extended boom to pump the liquid, and are simply using low-tech hose system.
Some secondary drilling also taking place into the bedrock.
Posted by O Suave Gigante on 2016-11-21 17:30:01
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