Nova Scotia's Highway 104 is the main artery for vehicular traffic connecting Cape Breton with Truro and all points in between. As part of their mandate, Nova Scotia Transportation and Infrastructure Renewal (TIR) is methodically converting the original 2-lane right of way into 4 lanes of divided highway. One of the last few stretches of Hwy 104 not yet expanded is located near Antigonish, Nova Scotia, and includes the West River Bridge. The bridge, being constructed by Dexter Construction Company Limited, consists of twin 2-span bridges, with 2 lanes eastbound and 2 lanes westbound. Geo-Foundations spent the summer and fall of 2011 constructing 152 micropiles for the permanent deep foundations of the bridges' 4 abutments and 2 centre piers.
Micropiles were selected by TIR for this site for two principal reasons. First, the overburden thickness varies greatly and the overburden layer is rife with cobbles and boulders. Second, the soft mudstone bedrock contains lenses and layers of highly varying thickness of much harder anhydrite. The small diameter, percussive drilling process involved in constructing micropiles proved well suited to overcoming both of these design and constructability challenges.
The deepest micropiles, at the northwest abutment, are over 30 metres deep. Abutment micropiles have factored axial compressive loading of 1214 kN; pier micropiles 1586 kN. All micropiles feature 75 mm / 517 MPa threadbar central reinforcement over their full embedment depth and 273 mm permanent casings throughout their overburden embedment. Rock socket diameter is 340 mm; bond length is 10 m at abutment micropiles and 12 m at pier micropiles. A total of 14 static tension tests were performed: 2 pre-production verification tests and 12 proof tests. The micropiles were completed in October 2011 and the bridge is due to be complete and ready for traffic in June 2012.
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