The city of Wabush, in Labrador, is a bustling hub fuelled by the mining and pulp & paper industries, and traffic jams during rush hour are not uncommon. As part of the infrastructure expansion required to keep up with the town's growth, a grade separation was constructed in 2011 to create a 2-lane underpass for NL Route 500, with the Wabush Mines / Bloom Lake Railway passing above.
Geo-Foundations was hired by constructor Grey Rock Mining to drill, install and tension 59 post-grouted soil tie back anchors to laterally restrain a sheet pile shoring system installed to enable excavation to the underside of the proposed rail bridge footings. Once excavation was completed however, the bedrock that was presumed to be present at the underside of Abutment 2 was in fact 3 metres deeper across most of the abutment footing's footprint. Without the option of taking the sheet pile system any lower and with the depth to rock at most pile locations insufficient for appropriate development of driven piles, the foundation design was changed, in August 2011, to micropiles.
All 40 permanent micropiles featured 5 m deep upper 340 mm diameter casings, some of which were embedded as little as 1.2 metres into rock, some as much as 4.5 metres into rock. Bond zone depth was 5 m, and all micropiles were reinforced with single 75mm / 517 MPa bar. Three pre-production tension load tests were performed to verify design adhesion assumptions, and static compressive proof tests to 2500 kN were carried out on 2 production micropiles. Enduring floods and bad weather throughout, Geo-Foundations' crews were able to complete micropile construction, including pre-production and proof testing, in time for the abutment to be constructed and the bridge commissioned prior to the start of winter.
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