Geosynthetics October/November 2020 - 11

Case Study

Reinforced embankments
for the causeway for a
North Wales bridge project
By Patricia Guerra-Escobar

T

he Pont Briwet Project in Penrhyndeudraeth, North Wales,
U.K., consisted of the replacement of a historic timber
trestle bridge with a new 446-foot (136-m) long concrete viaduct and the upgrade of the approach road to the north and
south of the crossing (Figure 1). The site is set within the
floodplain of the Afon Dwyryd (River Dwyryd), at the boundary of Snowdonia National Park, with tidal levels up to 15 feet
(4.6 m). The existing 22-span wooden viaduct dated back to the
1860s and carried the single-track Cambrian Coast Railway and
a single-lane road (Figure 2 on page 12). It had served the area
well for 160 years but was no longer suitable for modern transport requirements. The new viaduct provides a wider rail and
a two-lane road, as well as links the local footway and cycleway
networks on either side of the estuary. A key challenge of the
project was building the viaduct within the tidal estuary while
meeting the requirements on flood risk and water quality within
an Area of Conservation of Natural Resources Wales.
The new viaduct comprises seven 66-foot (20-m) integral
spans, formed from pre-stressed beams supported on concrete
crossheads and large diameter concrete piles installed into the
estuarine sands and gravels. For the causeway and ramps, it was
necessary to find a solution to construct temporary embankments to gain access for the construction of the foundations of
the viaduct within the river. The initial design considered permanent sheet-pile retaining walls; however, this solution would
have required a large amount of work to take place within the
tidal river and would have had a significant impact on the cost
of the project and the environment.

PROJECT HIGHLIGHTS
THE PONT BRIWET
BRIDGE PROJECT
CLIENT

Cyngor Gwynedd
LOCATION

Penrhyndeudraeth, Gwynedd,
North Wales, U.K.
GENERAL CONTRACTOR

Hochtief UK
PRINCIPAL DESIGNER

Hewson Consulting Engineers
SPECIALIST DESIGNER

Geosynthetics Ltd.
GEOSYNTHETICS MANUFACTURES
AND PRODUCTS

Tenax: Uniaxial Geogrid TT and
Biaxial Geogrid LBO HM: Tenax
Rhyno: Woven Geotextile

Patricia Guerra-Escobar is a principal
engineer for Geosynthetics Ltd. based
in Hinckley, Leicestershire, U.K.
All figures courtesy of the author.

www.GeosyntheticsMagazine.com

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Geosynthetics October/November 2020

Table of Contents for the Digital Edition of Geosynthetics October/November 2020

Geosynthetics October/November 2020 - Cover1
Geosynthetics October/November 2020 - Cover2
Geosynthetics October/November 2020 - 1
Geosynthetics October/November 2020 - 2
Geosynthetics October/November 2020 - 3
Geosynthetics October/November 2020 - 4
Geosynthetics October/November 2020 - 5
Geosynthetics October/November 2020 - 6
Geosynthetics October/November 2020 - 7
Geosynthetics October/November 2020 - 8
Geosynthetics October/November 2020 - 9
Geosynthetics October/November 2020 - 10
Geosynthetics October/November 2020 - 11
Geosynthetics October/November 2020 - 12
Geosynthetics October/November 2020 - 13
Geosynthetics October/November 2020 - 14
Geosynthetics October/November 2020 - 15
Geosynthetics October/November 2020 - 16
Geosynthetics October/November 2020 - 17
Geosynthetics October/November 2020 - 18
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Geosynthetics October/November 2020 - Cover3
Geosynthetics October/November 2020 - Cover4
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 1
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Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 3
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Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 8
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