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Nose Creek Sanitary Sewer Trunk Phase 2

Nose Creek Sanitary Sewer Trunk Phase 2
Date: 2015

The City of Calgary planned the installation of a 2.4 m wide sewer tunnel under 32 nd Avenue and Deerfoot Highway. The specifications stated that the installation was to be trenchless. AGRA Foundations Limited was contracted by Volker Stevin for the design and construction of a Tunnel Boring Machine retrieval pit.
This pit was to be 9 m deep with a clear span of at least 6.6 m x 6.6 m. The TBM also required a concrete wall to bore and exit through. A live telecommunications wire in the excavation area had to be considered during the design and execution of the works.
Ground conditions on site consisted of fill underlain by silty clay, followed by stiff clay.

Solution:

AGRA constructed a secant pile wall to support the 9 m excavation on the TBM exit side using wide-flange H-beams spaced at 3 m to allow for enough clearance for the TBM machine to go through. The other three sides were supported by beam and timber lagging. The timber lagging infill allowed to avoid the live wire. The walls were propped using an internal frame system to provide the required clearance.