NORTH AMERICA | REPORT
the bluffs along the western side of the Mississippi River are riddled with caves and karstic crevices,” says Allen Muehlher, assistant director of engineering. The TBM was recovered in late July this year after
a 205ft (62.5m)-deep recovery shaft was built and a 200ft (61m) tunnel was hand-mined back to the TBM. A replacement TBM is now being prepared. “A 13.5ft (4.1m)-diameter TBM with the capability of
probing and grouting through its face is currently being refurbished by Robbins,” says Muehlher. Tunnelling is expected to resume in January 2022 with completion scheduled for July. In addition to the launch and retrieval shaft, there are
14 bored shafts for drop pipes, vent pipes and fibre-optic conduits. “These shafts passed through a karstic zone located below the level of the Mississippi River but above the tunnel so they were blind bored,” says Muehlher.
MORE PROJECT CLEAR The next tunnel in Project Clear is the 10.9km Lower Meramec. The contractor is currently excavating the starter tunnel, drilling the drop and vent shafts, and installing the secant pile excavation system for the TBM retrieval shaft. Tunnelling is expected to be completed sometime in early 2025 and details of the TBM have not yet been finalised. Deer Creek was lined with a 12in-thick (304mm)
cast in situ concrete liner. Jefferson Barracks will have an 84in (2.13m) glass fibre-reinforced thermosetting resin sewer pipe with cellular concrete placed to fill the annulus between the pipe and the tunnel sidewall, while the Lower Meramec will have a 96in (2.44m) glass fibre- reinforced thermosetting resin sewer pipe. Other excavations for Project Clear include the largest
– the 14.4km, 30ft (9.1m)-diameter Lower and Middle River Des Peres storage tunnel, which will start in 2027; the three-mile River Des Peres Tributaries CSO tunnel; and the 3.2km, 22ft (6.7m)-diameter Upper River Des Peres CSO storage tunnel, which is due to start in 2032. In Seattle, Webuild Group’s US subsidiary, Lane, began
excavating the 4.2km, 5.5m-diameter storage tunnel for the Ship Canal Water Quality Project in June. The tunnel will prevent up to 75 million gallons (284m lit) of CSOs from flowing into the Lake Washington Ship Canal, Salmon Bay and Lake Union every year.
SECOND NARROWS WATER SUPPLY TUNNEL Further north, Metro Vancouver is undertaking five water supply tunnels that will meet current seismic standards. Excavation on the 1.1km-long Second Narrows tunnel, under Burrard Inlet was completed in early October 2021 (see box). Meanwhile, work on the 2.3km Annacis Water Supply Tunnel, which will run under the Fraser River, and the 1.4km Stanley Park Water Supply tunnel, is due to start in 2022. See box below for further information.
OTHER PROJECTS, TOO Water projects may currently be in abundance but other sector projects are also in progress or planned.
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