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PUC case study: defective gearbox blamed for tunnel-boring failure; contractor covered extraction costs
Summary
Staff presented a case study of the Alameda Siphon No. 4 project where a tunnel-boring machine failed; after a rapid multi-option assessment the PUC extracted and repaired the MTBM, found a defective gearbox, and reported that the contractor has covered extraction and repair costs so far.
The San Francisco Public Utilities Commission reviewed on March 22 how staff and contractors handled a tunnel-boring machine failure on the Alameda Siphon No. 4 seismic reliability project.
Julie Labonte, VISTA director, described the $61 million project and recounted that the micro-tunneling boring machine lost the ability to rotate its cutter head 13 days into operations. Staff evaluated four options (open cut, abandon/re-sequence, smaller recovery shaft with in-situ repair, or a larger recovery shaft to extract and shop-repair the machine) and chose to dig a larger recovery shaft. The…
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