The state will probably opt for twin bores — one for each of two parallel tracks.
That means as many as 72 miles of tunneling before 2022. "No way," said Leon Silver, a Caltech geologist and a leading expert on the San Gabriel Mountains.
Morales said the state does not have a detailed schedule showing how those milestones will be met.
He said the task will be left to future contractors.
Boston's 3.5-mile Big Dig was finished in 2007 — nine years behind schedule and at nearly triple the estimated cost.
Digging stopped on the 2-mile Alaskan Way tunnel under Seattle when a boring machine broke down in December 2013 and had to be retrieved for repairs, causing a multiyear delay with an unknown cost overrun.
"From a civil engineering perspective it is very, very ambitious — to put it mildly."Thomas O'Rourke, a Cornell University tunnel expert, also has doubts."My first gut reaction is that it is doable, but given the complex geology it is optimistically biased," O'Rourke said. It is going to depend on the complexity of the geology and the ground conditions."Monsees, who retired in 2013 from Parsons Brinckerhoff as its senior vice president for tunneling, added, "They are behind and need to get off their rear end and move." The rail authority declined to make any of its tunneling engineers available for interviews.