Tunnel Vision Issue 2 - JGL corporate newsletter - Flipbook - Page 17
SNOWDONIA VISUAL IMPACT PROJECT
Reducing the negative e昀昀ects of overhead electricity infrastructure within one
of the biggest National Parks in the UK.
As part of National Grid’s Snowdonia Visual
Improvement Project, Joseph Gallagher was appointed
to excavate and construct the Cilfor Shaft, a critical
component of the underground cable route designed
to reduce the visual impact of overhead electricity
infrastructure within Snowdonia.
The scope comprised the excavation of a 13.5m
diameter shaft to a depth of 60m below ground level,
providing reception facilities for a 4m diameter Tunnel
Boring Machine (TBM) advancing from the Garth site.
The shaft was constructed using a sprayed concrete
primary lining supported by 4m friction rock bolts
installed at 1.5m centres. Excavation progressed
through challenging hard mudstone geology using a
combination of hydraulic breaking and drill-and-blast
techniques.
The works also included waterproofing repairs to
secant piling installed by others and the construction
of a heavily reinforced concrete base slab to receive the
TBM breakthrough.
» Shaft excavated to 56.5m depth through hard
mudstone geology
» Successful adoption of drill-and-blast excavation
methodology
» Construction of heavily reinforced TBM reception
base slab
» Awarded subsequent contract for construction of
the permanent secondary shaft lining
» Delivery of a critical element of National Grid’s
Snowdonia Visual Improvement Project
Engineers before all else
josephgallagher.co.uk
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