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TEMPORARY BRIDGE INNOVATION WAS THE KEY TO PROJECT’S SUCCESS

PROJECT: CROWSNEST PASS, ALBERTA BRIDGE

TEMPORARY BRIDGE INNOVATION WAS THE KEY TO PROJECT’S SUCCESS

Crowsnest Pass is a small community nestled in the lowlands of the Rocky Mountains just inside Alberta’s western border with British Columbia. Located about 250 kilometres southwest of Calgary and 166 kilometres east of Cranbrook, the pass is an important stop on Highway 3, a major transportation corridor that runs between southern Alberta and southeastern B.C.

A bridge located on a secondary road just north of Highway 3 and about eight kilometres from Coleman, Alberta needed replacing. The bridge crosses the Crowsnest River.

The project involved installation of a temporary bridge crossing, removal of the existing timber and concrete bridge, and installation of a new 20m span two-lane concrete structure, including new erosion protection and approach work.

M. Johnston Construction Ltd., based in Cranbrook B.C., was awarded the contract to replace the bridge. Stantec Consulting completed the bridge’s design and administered the contract.

Right away, it was clear to M. Johnston that bridge demolition and construction would need to be done with minimal impact to the environment. The Crowsnest River is a classified waterway supporting a sensitive ecosystem with a number of aquatic species, some of which have been identified as sensitive or under threat.

Minimal fill required

A conventional approach would have had the contractor depositing fill into the creek in order to build a temporary access bridge while the new bridge was being constructed.

Instead, M. Johnston chose to draw on its inventory of ready-made temporary bridge structures in order to avoid disturbing the creek. The company constructed a three-span temporary detour bridge using six modular bridge sections to be placed alongside the existing 18.2m, (60-foot) three-span bridge, making the need for fill unnecessary.

“Rather than employing a single 60-foot-long structure with an extensive amount of temporary fill to bring the road approaches out to either end of that bridge, we chose to install three sections of bridge, totaling 48.7 m (160 feet) in length. So we essentially built a three-span, temporary bridge in order to bypass this single-span new bridge that we were constructing,” explained Matt Trousdale, project manager with M. Johnston Construction. To ensure minimal creek disruption, the bridge pilings were installed several metres back from the water’s edge so that pilings would not have to be driven into the creek bed. The original bridge had two piers anchored into the creek supporting three spans.

Not much room to maneuver

The tight approach to the existing bridge eliminated the option of running the detour upsteam or downstream. That meant butting the detour bridge right up against the existing one; only about 0.5 metres (1.6 feet) separated the two structures from curb to curb.

The detour bridge was placed in two days using temporary lock block pier foundations between spans, built onto riprap – a form of erosion protection – that was intended to be part of the final bridge design.

Approaches complete, the temporary detour bridge was then moved into place using a pair of Link-Belt 2800 excavators. “Those temporary bridges are designed, and are of such a weight, that two 30-tonne-class excavators can install them and remove them quite handily,” said Trousdale. Traffic was rerouted onto the temporary bridge.

The old bridge was demolished using an excavator and a 60-tonne Kobelco BM600 crawler crane needed to lift off the girder sections and to pull the timber piles out. All timber piles were successfully removed in their entirety. “We endeavour, where possible, to remove these piles completely, ensuring no further leaching of wood preservative into the soil and water.”

No-splice piles save time

The next step was driving the 14 steel piles for the new bridge using the BM600 with vertical travel lead and Bermingham B-21 diesel pile driver. The h-piles were driven to refusal on bedrock, approximately 15 metres (49.2 feet) below grade. M. Johnston used 18.3-metre (60-foot) pile sections to avoid splicing, allowing them to drive the abutment piles in just three days.

“Splicing of piles is often inevitable and we are well equipped to undertake this with our mobile equipment and inhouse CWB certified welders; however, it is always beneficial when you have the capacity to handle and install longer pile lengths, as was the case at Crowsnest, (to avoid splicing),” said Trousdale.

Wingwall piles – which stop the road fill at either end of the bridge from sloughing into the water – were placed under the temporary bridge. Trousdale said the modular structure of the detour bridge made this part of the operation a snap.

“We had to pick up, with two excavators, a section of temporary bridge, lift it out of the way, drive the wingwall pile, cut the wingwall pile off and then, with the two excavators, replace the piece of temporary bridge, all within the time period that we were allowed to close the road,” he said. “We were able to do all that work in a matter of about two-and-a-half to three hours.”

The new bridge consisted of cast-inplace concrete abutments with pre-cast concrete box girders, supplied by Rapid- Span Structures, built on top. Curb box girders weighing over 40,000 kilograms (88,000 pounds) required the use of a 250-tonne Link-Belt 3275 hydraulic crane carrying 71,000 kilograms (156,000 pounds) of counterweight for erection. Careful preparation of the site was required to locate the crane sufficiently close to the new bridge for the lifts to be successful.

“We were able to install all the girders in about six hours because of the way we prepared the site and the capacity of that particular crane,” said Trousdale.

The bridge surface consisted of a 150 mm (5.9-inch) thick, high-performance concrete (HPC) deck with 6m (19.7-foot) long, 250 mm (9.8-inch) thick approach slabs on either side.

A GOMACO C-450 deck finisher was used to finish both the bridge deck and approach slabs. The work was performed by Randy’s Decks and Diggers, based in B.C.’s West Kootenay region, with the help of Crowsnest Concrete. A 32m (105-foot) concrete boom truck was used to place the concrete, eliminating the need to reposition as the pour advanced.

Bridge construction from start to finish took about three months and Trousdale credits the temporary bridge innovation as the key to the project’s success.

“The unique element for us was access to the north in a temporary bridge,” he said. “The three-span temporary [bridge] was a novel idea proposed by us that certainly, in the end, proved to be an asset throughout the duration of the project.” HEG

A GOMACO C-450 deck finisher was used to finish both the bridge deck and approach slabs.

The finished bridge.