Environmental Science & Engineering - www.esemag.com - January 2004
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Mountain stream bridged on Olympic route in British Columbia
By Philip Carroll, P.Eng.,Armtec Ltd.
Highway No. 99 in British
Colombia represents the critical
transportation route between
the City of Vancouver
and the Resort Municipality of
Whistler, the sites of the 2010 Winter
Olympics. After years of study, public
input and preliminary design by UMA
Engineering Limited, the existing
route was divided into various sections
and awarded to consulting teams for
detailed design assignments under the
supervision of SNC Lavalin Inc.
Detailed design for the 7.2 km road
section between Culliton Bridge and
Cheakumus Canyon (approximately a
half hour drive north of Squamish and
south of Whistler), was prepared by
Earth Tech Canada Limited, widening
the road to three lanes and straightening
its vertical and horizontal alignment
to improve driver safety. Conroy
Creek, a mountain stream, home to a
resident population of Rainbow Trout,
crosses Highway No. 99 in this section
of highway via an existing Multi-Plate
Pipe Arch, measuring approximately
2.4m wide x 2.1m high.
As part of the design process,
Armtec provided pre-design technical
support to Earth Tech by offering a
Bridge-Plate cross-section shape suitable
for the span, rise, cover and
hydraulic end requirements for the
crossing. To provide improved fish
passage, the structure was designed to
be on a flat gradient, having an open
bottom arch design with a span of
10.247m and rise of 4.843m.
As part of the tender and quotation process, Armtec prepared
and distributed a set of preliminary installation and
assembly drawings for a 30.08m long Bridge-Plate
Structure along with a preliminary design for cast-in-place
concrete footings and gravity end walls. Following award
of the $18.2 million dollar construction contract to Bel
Contracting Limited, Armtec provided input on how the
structure could be lengthened to reduce and/or eliminate
the need for the end walls.
After detailed analysis by Bel and Armtec, the structure
was lengthened to 33.68m and the upstream end wall was
eliminated in favour of a rip-rap/non-woven geotextile
(Armtec 350) slope and cast-in-place end collar. The downstream
end was redesigned with a cast-in-place end collar
in conjunction with Lock-Block wingwalls, reinforced with
Armtec Mirafi 8XT Polyester Geogrid.
Armtec retained McElhanney Consulting Services to
offer detailed design and field certification services for the
cast-in-place concrete footings, downstream end wall and
upstream slope treatments. McElhanney also conducted an
overall geometry check of how the roadway fill slopes tied
into the end walls.
Following installation of the 2m wide x 0.5m high footings
by Newport Structures Limited, the 28 ring Bridge-
Plate was assembled in approximately four days, with one
and a half days extra for tightening.
With the support of an Armtec engineer to provide onsite
quality control, Bel crews started installation of the
critical backfill gravel compacting in 200mm high lifts on
either side of the structure. Within four and a half days, Bel
finished the majority of the backfill placement to approximately
1m above the crown of the structure. The Bridge-
Plate Structure was assembled, tightened and backfilled in
under 10 working days, making it possible to finish the
project by the fish window deadline.
During the backfill process, Armtec provided continuous
monitoring of the structure by installing six monitoring
stations and logging chord measurements using a handheld
electronic distance measurement (EDM) tool. Gravel
quality and compaction tests were also monitored on an
ongoing basis.
To armour the footings inside the structure without having
to place large boulders against the Bridge-Plate and
risking damage, Bel installed 25kg rip-rap directly above
the footings and pumped concrete into the voids. To mimic
a natural stream bed, the design also called for the placement
of a 300mm thick layer of fish gravel above the riprap
layer.
Following the removal of the stream diversion and
restoration of the creek flow through the structure, Conroy
Creek assumed the look of a pool area within the confines
of the structure, a great resting place for the resident population
of Rainbow Trout.
After a few weeks, the drainage area was subjected to a
flood event of historical proportions and the Conroy Creek
structure ran at/near its hydraulic capacity. With the concrete
collars and end treatment design in place, the structure
was able to accommodate the flood flows.
Philip Carroll is Armtec’s BC Region Engineer. Contact
e-mail: pcarroll@armtec.com.
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