Newlands Cross Upgrade EIS - European Investment Bank

South Dublin County Council N7 Newlands Cross Upgrade
Environmental Impact Statement
Arup Consulting Engineers
Many of the items listed above are similar to both of the proposed schemes and therefore are
not discussed in this report. Those issues which are not similiar to both schemes are addressed
in the following sections.
3.7.2 Construction Methodology
The following sections describe how both of these options would be constructed.
3.7.2.1 Option 1 – Overpass
The Overpass option would be constructed in seven stages as follows as depicted in Figures
4.10 – 4.16 inclusive:
Stage 1: Temporary traffic diversions will be constructed offline and to the south of the
proposed overbridge location. This will include the construction of as much of the permanent
works as is feasible. The temporary diversions will facilitate the diversion of the Naas Road
(N7) from its current alignment and enable construction works to commence to the north of
the scheme. Temporary traffic lights and road markings will also be installed for traffic
management purposes at this time.
Stage 2: The abutment walls and the bridge piers in the central island will be constructed.
Reinforced soil approach embankments will also be constructed at this time.
Stage 3: Precast beams will be lifted into place during a series of overnight road closures.
Glass fibre reinforced concrete permanent formwork will be placed between precast beams, to
enable the construction of the deck slab to proceed above the live traffic on the
Fonthill/Belgard Road (R113) beneath.
Stage 4: The Reinforced Concrete deck slab and parapet edge beams will be cast. Deck
surfacing, lighting and drainage will be added to the overbridge structure
The road pavement on the approach embankments will be constructed together with the
drainage, lighting, noise barriers (where required) and central reserve vertical concrete barrier.
Stage 5: Traffic will be redirected onto the overbridge structure. The temporary westbound
diversion to the south of the overbridge will be removed and the final highway arrangement
for the westbound merge and diverge lanes will be constructed. The highway arrangement to
the north of the overbridge structure will also be constructed.
Stage 6: All remaining highway upgrade works will be completed including the landscaping,
lighting and drainage elements.
Stage 7: Final Highway Scheme Arrangement
3.7.2.2 Option 2 – Underpass
This Underpass would be constructed in seven stages as follows:
Stage 1: Construct the temporary road diversion to the south of the underpass to facilitate the
temporary diversions of the eastbound and westbound carriageways. Traffic management
measures will also be addressed at this time.
Stage 2: Construct a Secant Piled Wall to the underpass. The bridge deck to carry the
Fonthill/Belgard Road (R113) over the underpass is to be built in two stages and the
excavation is to use the top-down construction method.
Excavation for the underpass will commence at the remote eastern and western ends of the
project. At these locations the underpass will be constructed in open cut and utilise reinforced
concrete retaining walls. As much of the excavation as possible will take place within the
vicinity of the Secant Piled Walls but stopping within a safe distance of the bridge structure.
December 2007 Page 21