LA Times article on rail which infers the FS approval goes all the way.
...The bullet train will require about 20 miles of tunnels under the San Gabriel Mountains between Burbank and Palmdale, involving either a single tunnel of 13.8 miles or a series of shorter tunnels.
As many as 16 additional miles of tunnels would stretch under the Tehachapi Mountains from Palmdale to Bakersfield.
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.
Can it meet that schedule?
"No way," said Leon Silver, a Caltech geologist and a leading expert on the San Gabriel Mountains. "The range is far more complex than anything those people know."
Herbert Einstein, an MIT civil engineer and another of the nation's top tunneling experts, said, "I don't think it is possible."
"Having looked at a number of these long tunnels, [the California] plan is aggressive," said Einstein, who has consulted on a 35-mile-long tunnel under the Swiss Alps. "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. "There are a lot of unknowns. 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....
Silver, the Caltech geologist, said the San Gabriels' oldest rocks formed 1.7 billion years ago, 200 miles to the south. They became highly fractured as they were shoved north by movements of the Earth's crust.
Tunnelers will find that rock types change frequently, creating conditions that are among the most challenging for tunneling.
"If it were one single mass of granite, it would be easy to drill through and provide structural support," said Silver, who trained the Apollo astronauts in lunar geology and pioneered the dating of the San Gabriel Mountains. "But everything in the arc has been bent, shoved, stretched, compressed and metamorphosed."
The mountain range lies in a giant crescent between two major faults, the San Gabriel and the San Andreas, which separates the Mojave Desert on the North American tectonic plate from the Los Angeles Basin on the Pacific plate.
Between the two major faults are many secondary faults. Some are vertical strike-slip faults that move laterally, and some are thrust faults that move vertically. Some are horizontal, traveling through the ground at various depths.
"Every one is going to slow things down tremendously," said Monsees, the former Parsons Brinckerhoff tunnel expert.
A 2012 report by Parsons Brinckerhoff, obtained by The Times, warned the rail authority that the "seismotectonic complexity ... may be unprecedented" and that the rail route would be crossing faults classified as "hazardous."
The faults, changes in rock types and shattered rock cause many headaches, sometimes requiring changes in cutter heads. Doing so means stopping the machines while technicians crawl to the front to manually swap out as many as 40 to 60 cutter heads. A full swap of cutter heads can take an eight-hour shift, the engineers said.
Shattered rock causes additional problems in supporting the overhead formations, requiring workers to bore 10-foot-long holes into the ceiling and insert rock bolts that knit together blocks that weigh tons.
Morales, the rail agency chief executive, said he did not know what rates of advance will be possible. He said that will be determined by the contractors the state hires.
In good rock, such as limestone or chalk, TBMs can advance 100 to 200 feet a day. But in fractured mixed rock through fault zones, the advance rates can slow to 10 to 20 feet a day, Einstein of MIT said.
Einstein's estimate is endorsed by other engineers, including one who has worked closely on the bullet train project and told The Times that 10 feet a day is the likely rate of advance.
The schedule will depend in part on the number of TBMs and other smaller tunneling machines the state uses, with each machine and its crews adding to costs. The 36 miles of tunnels include a mix of short and long segments, dug by different methods.
The longest possible tunnel, described as one alternative in state documents, would stretch 13.8 miles under the Angeles National Forest. Assuming TBMs started at both ends and advanced at 20 feet a day for 261 days a year, the tunnel would take seven years to complete — finishing in 2026. At an advance rate of 10 feet a day, the time would double to 14 years.
The state is considering a different route under the national forest that would instead require a tunnel of just 7 miles. It would take 31/2 to seven years to dig, based on the same advance rates. But that route faces significant political opposition.
Only after the tunnels are dug can the next phase begin: installing track and other equipment in the 36 underground miles. By way of comparison, the Swiss are taking more than four years after tunneling to install track and equipment in the 35.4-mile-long Gotthard Base Tunnel through the Alps, a project spokesman said. Contractors will take an additional nine months to test the systems.
The route through the Tehachapi Mountains from Palmdale to Bakersfield, crossing several major faults, is at an even earlier level of planning.
The last formal analysis was issued more than three years ago. It said that as many as 16 miles of tunnels and as many as a dozen viaducts would be required. The possible routes were later found to be problematic because they are steep and would conflict with a massive wind farm. The agency is working on a new analysis....
