Nationally and internationally-recognized seismologists, geologists and engineers recommended Wednesday that a subway station in Century City should be built under the intersection of Constellation Boulevard and Avenue of the Stars to avoid two earthquake faults in the area.
Speaking to the Metro Board of Directors Planning Committee, experts also said that tunneling under parts of the Beverly Hills High School campus would not compromise the structural integrity of existing structures, interfere with future building plans or create perceptible noise or vibrations on school grounds.
“The Project is not expected to pose new threats to the students, faculty, or community as a result of its construction and operation,” states the Executive Summary of one of the two written reports by the experts on tunneling and seismic issues in the Beverly Hills, Century City and Westwood areas. The Executive Summaries can be viewed here and the Powerpoint presentation given to the Board committee here. Metro is working to get the full reports posted to this same website by tomorrow.
In addition, experts said that drilling and tests performed by Metro in the Beverly Hills, Century City and Westwood areas found less methane and hydrogen sulfide than along parts of the existing subway in downtown Los Angeles and other parts of the proposed line. Field work and research failed to detect any active or inactive oil wells on the school campus that would be in the path of potential subway tunnels.
The information contained in these reports will be used by Metro staff to develop their recommendation for a subway route and Century City station location as part of the Westside Subway Extension’s Final Environmental Impact Statement/Report (Final EIS/EIR), which is scheduled to be released this winter. The final decision on the subway’s route will be made by the Metro Board of Directors, likely in early 2012.
Some of the world’s leading seismologists and tunneling engineers were involved in preparing the reports or independently reviewing them for Metro and Parsons Brinckerhoff, the primary contractor hired by the agency to help plan and perform preliminary design for the subway alignment.
Among the experts was Dr. James Dolan of USC, who performed pioneering research on blind-thrust faults in the Los Angeles area. Among the reviewers was Dr. Lucy Jones of the U.S. Geological Survey and the California Institute of Technology. Both spoke to the Board on Wednesday. Biographies of the scientists involved will be posted here shortly.
Two other experts who spoke today were Dr. Harvey Parker, an engineer and former President of the International Tunneling Association, and Dr. Paul C. Jennings, a Professor of Civil Engineering and Applied Mechanics, Emeritus, at the California Institute of Technology.
The reports were compiled as part of the ongoing Final EIS/EIR for the Westside Subway Extension, which will extend the Purple Line for nine miles to the Veterans Affairs Hospital in Westwood. The project is funded in part by the Measure R sales tax increase approved by 68 percent of Los Angeles County voters in 2008.
Although most of the subway’s route was approved by the Board last year, the Board requested more geotechnical and engineering studies before finalizing the Century City station location and the subway’s alignment between Beverly Hills and Westwood.
As part of those studies, Metro planners have been working to precisely map the location of two known earthquake faults in the Century City area, the Santa Monica Fault and the West Beverly Hills Lineament, now considered to be the northern extension of the Newport-Inglewood Fault Zone.
Two potential alignments for the subway between Beverly Hills and Century City remain under study. One would follow Wilshire Boulevard and then continue west under Santa Monica Boulevard. The other would be located to the south and tunnel beneath parts of the Beverly Hills High School campus before turning west to a subway station at the intersection of Constellation Boulevard and Avenue of the Stars.
The approximate locations of the Santa Monica Fault and the West Beverly Hills Lineament have been known for years, but the exact location had not been evaluated through underground investigations. To generate the needed data, Metro contractors drilled over 200 boreholes and penetrometer tests in Century City, Beverly Hills and Westwood, as well as other tests using sound waves to develop profiles of the area’s underlying geology.
Experts found that strands of the active Santa Monica Fault are under the intersection of Santa Monica Boulevard and Avenue of the Stars.
An alternative station location on Santa Monica Boulevard and Century Park East, studied as a part of the Final EIS/EIR, is located within the West Beverly Hills Lineament fault zone, an extension of the Newport-Inglewood Fault that triggered the 1933 Long Beach earthquake.
The fault report concluded that there is no unequivocal evidence of a long enough section of Santa Monica Boulevard to accommodate a station in the Century City area outside of an active fault zone.
According to the executive summary of the report, released on Wednesday:
“No evidence of faulting was found on the proposed Constellation Boulevard Station site. Based on the results of these fault investigations, there is clear evidence that the proposed station locations on Santa Monica Boulevard (both east and west) would be in active fault zones, and are not viable options for station locations. The proposed station on Constellation Boulevard would not be within an active fault zone.”
Experts said that because stations are continuously occupied by people, they should not be built in active fault zones because such stations are difficult to design and faults are places where ground deformation will occur.
However, experts reported that there is evidence from Los Angeles and around the world that subway tunnels can perform well during earthquakes because tunnels tend to move with the ground rather than sway like buildings. Metro’s subway returned to service quickly after the 1994 Northridge quake, as did BART trains following the 1989 Loma Prieta quake in the Bay Area. In both earthquakes, freeway bridges collapsed.
The Westside Subway Extension will have to cross two active fault zones. “There are numerous proven designs and construction means and methods to safely build a tunnel through fault zones,” states the Executive Summary of the tunneling report. “Design methods include building a larger diameter tunnel and/or a very strong but flexible lining to withstand several feet of movement without collapse and still be repairable.”
Experts also explained that it’s best for tunnels to cross faults at sharp angles to minimize exposure to them.
Other issues covered in the reports in greater detail included:
•The top of the twin subway tunnels for the project is expected to be 55 feet to 70 feet below the Beverly Hills High School campus. The tunnels are expected to pass under the Beverly Hills Unified School District administration building, the high school’s tennis courts, the southern wing Building B and the school’s lacrosse fields.
•There is not expected to be any damage to campus buildings as a result of ground settlement from tunneling, which will be done with pressurized closed-face tunnel boring machines that provide support to the ground as they dig. These types of machines were successfully used to dig the tunnel on the Metro Gold Line Eastside Extension.
•Only one abandoned oil well was mapped to lie within the tunnel alignment — and is beneath a parking garage in Century City. This one “anomaly” that could be related to old oil well infrastructure was found underground on the school campus in the area near the lacrosse field and was outside the proposed tunnel alignments. Further exploration of the tunnel alignment to confirm that it is clear of oil wells is planned.