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									BC highway



Bridge plate structure
meets tight deadline
The Sea-to-Sky highway – B.C.
Highway 99 – is praised by many for
the beautiful landscapes it traverses.
The upgrading of the 7.2km section
between Culliton Bridge and Cheak-
umus Canyon called for widening the
road to three lanes and straightening
its vertical and horizontal alignment
to improve driver safety.
One consideration for contractors
was Conroy Creek, a mountain
stream hosting rainbow trout, which
crosses the highway via an existing
multi-plate pipe arch, measuring ap-
proximately 2.4 m wide by 2.1 m
high.
         Detailed design for the proj-
ect was prepared by Earth Tech Can-
ada Ltd., while Armtec provided pre-
design technical support by offering
a bridge-plate cross-section shape
suitable for the span, rise, cover and
hydraulic end requirements for the
crossing. To improve fish passage,
the structure was designed to be on a
flat gradient, having an open-bottom
arch design with a span of 10.247 m
and rise of 4.843 m.
         The $18.2-million dollar
contract was awarded to Bel Con-
tracting Ltd. After detailed analy-
sis, the structure was lengthened to
33.68 m and the upstream end wall
was eliminated in favour of a rip-rap
/ non-woven geotextile (Armtech
350) slope and cast-in-place end col-
lar. The downstream end was rede-
signed with a cast-in-place end col-
lar in conjunction with Lock-Block
wingwalls, reinforced with Armtec
Mirafi 8XT Polyester Geogrid.
         McElhanney        Consulting
Services provided detailed design
and field-certification services for
the cast-in-place concrete footings,
downstream end-wall and upstream
slope treatments. It also conducted
an overall geometry check of how
the roadway fill slopes tied into the
end walls.
                                         reprinted from On-Site March 2004 issue
e    The 28-ring bridge plate
      was assembled in about
    four days, with a half day
               for tightening.




                                 Following installation of the 2 m         To armour the footings inside the
                                 wide by 0.5 m high footings by            structure without having to place
                                 Newport Structures Ltd., the 28-ring      large boulders against the bridge
                                 bridge plate was assembled in ap-         plate and risk damage, Bel in-
                                 proximately four days, with one and       stalled 25-kg rip-rap directly above
                                 a half days extra for tightening.         the footings and pumped concrete
                                          Bel crews started installa-      into the voids. To mimic a natural
                                 tion of the critical backfill gravel,      stream bed, the Design also called
                                 compacting in 200-mm high lifts on        for the placement of a 300-mm thick
                                 either side of the structure. Within      layer of fish gravel above the rip-rap
                                 four and a half days, Bel finished the     layer.
                                 majority of the backfill placement                  Following the removal of
                                 to approximately one m above the          the stream diversion and restoration
                                 crown of the structure. The bridge-       of the creek flow through the struc-
                                 plate structure was assembled, tight-     ture, Conroy Creek assumed the look
                                 ened and backfilled in under 10            of a pool area within the confines of
                                 working days, making it possible to       the structure – a great resting place
                                 finish the project by the fish-window       for the resident population of rain-
                                 deadline.                                 bow trout.
                                          During the backfill process,               After a few weeks of the
                                 the structure was monitored contin-       structure being constructed, the
                                 uously by installing six monitoring       drainage area was subjected to a
                                 stations and logging chord measure-       serious flood event and the Conroy
                                 ments using a hand-held electronic        Creek structure ran at very near its
                                 distance-measurement tool. Armtec         hydraulic capacity. With the con-
                                 also monitored gravel quality and         crete collars and end treatment de-
                                 compaction tests on an ongoing ba-        sign in place, the structure was able
                                 sis and coordinated the inspection        to accommodate the flood flows.
                                 visits by McElhanney.
                                                                           This article was based on material
                                                                           provided by Armtec Ltd.

                                 reprinted from On-Site March 2004 issue

								
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