Home > FAQs > The proposed project is a 40-foot diameter TBM that is tunneling 40 miles. There may be four TBMs, but the process is the same. What happens if the TBM gets stuck? What about safety in the tunnels?
There will be multiple TBMs on the project, and they are all expected to use a pressurized face method of excavation (i.e., earth pressure balance and/or slurry shield TBMs). Maintenance shaft spacing would be about every 5 miles and would be sized to allow for major repairs of the TBM at those locations, if necessary. Because the TBM would have major maintenance reviews and repairs approximately every 5 miles, it would not require major repairs between the shafts. The specifications would also require that many of the major TBM parts; like the main bearing, seals and other parts; would be replaceable from within the tunnel in case some repairs are necessary between shafts. This approach is actually more conservative than that recommended by the ITR. Worker safety in tunnels is dictated by the regulations provided under Cal/OSHA’s Tunnel Safety Orders, which are very prescriptive in terms of the working conditions for such essential items as adequate ventilation, illumination, ingress/egress and other items to comprehensively address worker safety.