River Dargle Flood Scheme, Bray, Co. Wicklow: P1240961_a
River Dargle Flood Defence Scheme.
These images were taken during the second week of March 2017.
These are the critical stabilisation works at the Silverbridge site, adjacent to the N11 dual-carriageway:
Back in November 2014, we'd 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’ had 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 were 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).
=================================================
Previously the guys drilled and sunk 4+metre deep reinforced tubing and rods along a newly laid concrete base. Those stubs were then used to attach steel rod cradles -- which, in turn, were filled with poured concrete. Result - the wall quickly rises. Variation on the method they've used elsewhere along this stretch of the river.
A continuous stretch of protective wall has now been poured, and joined up with the section originally erected back in 2014.
As we can see from the side-on shot, the base of the wall has pre-cut openings for the retaining pins that have been driven into the side wall of the roadside cliff. These have been sealed and capped.
Progress has been rapid, the full stretch of wall is completed, and the guys are now working on back-filling the empty space between the protective wall and the roadside rock face. You don't just throw in a few trucks loads of soil and hope for the best. You load, layer, level and compress.
By now the guys had clearing away material used to build access ramps down into the riverbed.
The thought crossed had my mind -- in doing so (removing the stone-filled gabions etc,) are they potentially exposing the river bank on that side to erosion, slippage etc?
We know the destructive force of fast running waters. Hell, this is precisely why the protective works have been carried out along the rest of the stretch, down to the Bray Harbour. Unless they have other plans to stabilise it, what is going to be left here is loose soil -- very close to the access road into the halting site itself.
Now that we can see the cleaned, exposed riverbank, we can see a substantial bedrock. Clearly this is not liable to subsidence. And there evidence that sections of the slope had already been 'nailed' * to prevent slippage. But, in talking to the guys there, it would seem that further 'nailing' might be required later in the year.
Some repair/reinforcing work is going on here to protect the (old) buttress that supports the pipework carrying water to the Bray region.
*
Soil nailing is a construction technique that can be used as a remedial measure to treat unstable natural soil slopes or as a construction technique that allows the safe over-steepening of new or existing soil slopes.
The technique involves the insertion of relatively slender reinforcing elements into the slope – often general purpose reinforcing bars (rebar) although proprietary solid or hollow-system bars are also available.
Solid bars are usually installed into pre-drilled holes and then grouted into place using a separate grout line, whereas hollow bars may be drilled and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down the hollow bar as drilling progresses.
River Dargle Flood Scheme, Bray, Co. Wicklow: P1240961_a
River Dargle Flood Defence Scheme.
These images were taken during the second week of March 2017.
These are the critical stabilisation works at the Silverbridge site, adjacent to the N11 dual-carriageway:
Back in November 2014, we'd 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’ had 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 were 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).
=================================================
Previously the guys drilled and sunk 4+metre deep reinforced tubing and rods along a newly laid concrete base. Those stubs were then used to attach steel rod cradles -- which, in turn, were filled with poured concrete. Result - the wall quickly rises. Variation on the method they've used elsewhere along this stretch of the river.
A continuous stretch of protective wall has now been poured, and joined up with the section originally erected back in 2014.
As we can see from the side-on shot, the base of the wall has pre-cut openings for the retaining pins that have been driven into the side wall of the roadside cliff. These have been sealed and capped.
Progress has been rapid, the full stretch of wall is completed, and the guys are now working on back-filling the empty space between the protective wall and the roadside rock face. You don't just throw in a few trucks loads of soil and hope for the best. You load, layer, level and compress.
By now the guys had clearing away material used to build access ramps down into the riverbed.
The thought crossed had my mind -- in doing so (removing the stone-filled gabions etc,) are they potentially exposing the river bank on that side to erosion, slippage etc?
We know the destructive force of fast running waters. Hell, this is precisely why the protective works have been carried out along the rest of the stretch, down to the Bray Harbour. Unless they have other plans to stabilise it, what is going to be left here is loose soil -- very close to the access road into the halting site itself.
Now that we can see the cleaned, exposed riverbank, we can see a substantial bedrock. Clearly this is not liable to subsidence. And there evidence that sections of the slope had already been 'nailed' * to prevent slippage. But, in talking to the guys there, it would seem that further 'nailing' might be required later in the year.
Some repair/reinforcing work is going on here to protect the (old) buttress that supports the pipework carrying water to the Bray region.
*
Soil nailing is a construction technique that can be used as a remedial measure to treat unstable natural soil slopes or as a construction technique that allows the safe over-steepening of new or existing soil slopes.
The technique involves the insertion of relatively slender reinforcing elements into the slope – often general purpose reinforcing bars (rebar) although proprietary solid or hollow-system bars are also available.
Solid bars are usually installed into pre-drilled holes and then grouted into place using a separate grout line, whereas hollow bars may be drilled and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down the hollow bar as drilling progresses.