PUC case study: defective gearbox blamed for tunnel-boring failure; contractor covered extraction costs

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 California Department of Fish and Game granted an extension of the October 15 permit deadline to November 30 to allow recovery work.

Labonte said the machine was extracted and inspected in a shop; engineers found the gearbox defective and replaced it. Tunneling resumed nine days later and completed “well before the new deadline” established by the permitting agency. To speed resolution, staff entered an early cost-sharing agreement with the contractor but reported that the contractor has covered the actual extraction and repair costs to date.

Commissioners probed liability and cost allocation. Labonte said staff’s assessment attributed the failure to a defective gearbox and the contractor’s equipment; the PUC has directed its team to be ready for any contractor change order but had not yet received one. Assistant General Manager Harlan Kelly noted the city is self-insured and that claims tied to differing site conditions could transfer costs to the city if demonstrated, but staff emphasized their conclusion that the contractor bears responsibility for the gearbox defect.

Why it matters: The project is a seismic reliability ‘lifeline’ across the Calaveras Fault; Labonte stressed the importance of the project to maintain service west of the Irvington Tunnel in the event of a seismic event. Staff also emphasized that pre-established procedures, a construction management information system (CMIS) and an escalation ladder allowed for a rapid, collaborative response.

Next steps: Staff said they will seek approval in April for contract change-orders exceeding 10% for four contracts related to other work; they also plan a formal lessons-learned review and may tweak specifications to reduce future risk, including reviewing contractor capacity and prequalification criteria.