NORTH AMERICA | REPORT
in a day, equating to 45m. The project is anticipated to be Canada’s largest wastewater outfall.
CLEARWATER PROJECT In late September, tunnelling was due to begin on the Clearwater Project, a new seven-mile tunnel for the Los Angeles County Sanitation District. Construction on the project, which addresses ageing infrastructure that falls short of current seismic standards, began in 2019. Tunnelling is expected to be completed in early 2025 and the project is scheduled to finish in 2027. The Herrenknecht slurry TBM, named Rachel, has
been equipped to deal with the varied geological conditions along the length of the tunnel and the two distinct geological settings at each end. “The northern section is predominantly silts, sands,
clays and gravels encompassing the Lakewood Formation and San Pedro Sands soil groups,” says Russ Vakharia, the District’s construction manager for the project. “The southern section is a predominantly ‘weak rock’ group with varied layers of siltstone, dolomite, claystone sandstone and less amounts of basalt that is characterised as ‘hard rock’.
Vakharia adds: “The varied lithologies specific to the
rock portion may create unbalanced loading during excavation. Additionally, consistent with many portions of the Los Angeles area, the alignment has been classified as ‘gassy’.” The tunnel has more than 30 curves and will
be excavated from a single shaft; there will be no intermediate shafts. To add to the complexity, two fault zones – the Palos
Verdes and the Cabrillo – transverse the alignment, and in the southern rock there are water pressures of up to 10bar, an overburden of more than 122m and squeezing ground conditions. To mitigate these challenges, the TBM has been fitted
with several features, including six large filter presses that augment the slurry treatment plant to handle fines separation from the slurry mixture. For the southern rock portion, the TBM can provide additional thrust capacity (up to 135MN), and has a tapered shield, equipment designed to operate at up to 10bar pressure, instrumentation and equipment to monitor and measure rock convergence, as well as the means to consolidate the ground ahead of the TBM.
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Above:
On MSD Project Clear in Missouri, the TBM broke through on the Deer Creek tunnel in January 2020 and work is now under way on the Jefferson Barracks and Lower Meramec tunnels
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