Prior to 2008, Toronto's Morningside Avenue was restricted by a decades-old, single lane underpass at its crossing of the Canadian Pacific Railway (CPR). A grade separation to create a six-lane subway beneath the CPR necessitated construction of seven new, deep-founded structures: 2 abutments, 1 pier and 4 retaining walls. These structures are all supported by micropile foundations designed and constructed by Geo-Foundations.
Micropiles were proposed post-tender to prime contractor Soncin Corporation as an alternative to the specified 324 mm driven tube piles. The site is underlain by a significant aquifer under artesian head, and the tendered scheme was predicated on terminating the piles at a pre-determined, safe distance above the top of the aquifer. The proposed - and eventually accepted - micropile scheme was based on using 5 micropiles for roughly every 3 driven piles in order to reduce the unit loading on individual micropiles to acceptably low loads so that no micropile had to be embedded any lower than 5.6 metres beneath the underside of any structure.
In order to support the staging necessary to keep both the CPR tracks and Morningside Ave. open throughout construction, the micropiles were constructed inside 8 metre wide excavations with several overhead obstructions reducing the working headroom to just 6 metres.
A total of 357 Titan 52/26 micropiles were installed in place of the 223 specified driven piles. Five load tests were performed: 2 sacrificial, pre-production load tests and 3 proof tests. Typical magnitude of applied test loading was 720 kN, and the locations of the load tests were spread across the three bridge foundations - 2 tests at the east abutment, 1 test at the centre pier and 2 tests at the west abutment. Production micropile construction was completed in 4 weeks.
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