Palmdale-Burbank bullet train tunnel possible, study says
March 15, 2016
• Would hardly be the longest tunnel
• “The many long tunnels in use around the world today hold valuable lessons”
Drilling a tunnel 16 miles through the San Gabriel Mountains in Southern California for the proposed bullet train would not be anything exceptional in terms of engineering, suggests a new report Tuesday from the Mineta Transportation Institute at San Jose State University.
One route proposed for the high-speed passenger system to get to Los Angeles is through the mountain range from Palmdale to Burbank.
But it’s such a tough and costly project, the California High-Speed Rail Authority has switched its plans to first connect the Bay Area with the Bakersfield area and put off the getting-to-LA issue. The Mineta report (which can be downloaded from the link below) does not examine the costs of the tunnels.
But in his desktop study that compiled information from long tunnels worldwide for the Mineta Transportation Institute, Jae-Ho Pyeon, an assistant professor in the Department of Civil and Environmental Engineering at San José State University, found a number of tunnel projects worldwide that are engineered specifically for high-speed trains.
The study, Trend Analysis of Long Tunnels Worldwide, created a database that breaks down attributes of successful tunnels around the world, discussing what the trends are for feasibility of long tunnels, the optimal configurations for HSR tunnels that cover significant distances, and what safety features best protect passengers and first responders in case of emergencies.
“With advances in tunneling technology, the many long tunnels in use around the world today hold valuable lessons” for the California project, “particularly with respect to minimization of ground disturbance and improved passenger and operator safety,” says Mr. Pyeon.
The key findings include:
• Five HSR tunnels of the same length as – or longer than – the proposed Palmdale-Burbank connection have been built, worldwide. Another six are in the planning or construction stages.
• HSR tunnels have been built that exceed 30 miles; a tunnel longer than 16 miles is considered feasible by world engineering standards.
• The double-tube, single-track configuration is becoming standard in most areas because it is considered the safest. These are normally connected by cross-passages that assist with maintenance, improve ventilation, and can be used for escape in the event of emergencies. Refuge areas are often included in long tunnels as an added safety precaution.
• Both tunnel boring machines (TBMs) and conventional tunneling methods (drilling and blasting) are popular for rail tunnel projects. Many projects combine the two techniques. TBM is used because of its higher advance rates, and conventional means are employed in terrains that feature difficult rocks, highly variable rocks conditions, and enhanced risks of water inflow under high pressure.
• Tunnel excavation spoil management is usually critical in reducing the environmental impact of tunnel construction.