Home > FAQs > The ITR report sought to determine if CEQA could have an approach for the unknowns. How can that comment be assimilated? The Big Bertha TBM used on the Alaska Way Viaduct got stuck 1,000 feet into the tunnel drive. How is that type of possibility going to be addressed from the engineering point of view?
During the ITR team review, it was discussed that use of maintenance shafts approximately every 5 miles with full maintenance procedures at those shafts would substantially reduce the probability of failure between shafts. In addition, it is understood that tunnel boring machine technology is continually evolving and many of the maintenance procedures can be completed from within the tunnel. The ITR team documented one case study that included a main bearing being replaced from inside the tunnel. Technology will continue to change significantly five years from now when the Delta Conveyance program is projected to be under construction. During the design phase, additional ITR reviews will be conducted to incorporate new technologies. DCA is being conservative in planning full maintenance shafts every 5 miles in order to avoid the need for an emergency shaft.