Silicon Valley Rapid Transit Project (BART Extension to San Jose)
San Jose, California
Santa Clara Valley Transportation Authority (VTA)
As part of the proposed extension of the BART rapid-transit system to San Jose (known as SVRT), ATS completed an applied research project that studied ground-vibration mitigation measures. The overall goal of the project was to develop a strategy for mitigating the vibration impact from the proposed extension. Through detailed measurements of how existing vibration mitigation measures are performing on the BART system and preliminary computer modeling, ATS demonstrated that much less expensive measures would be just as effective as the originally proposed measures.
The extension of the BART rapid-transit system passes within 50 to 100 feet of numerous residences in Milpitas and north San Jose. Given that 800-foot long trains would be passing these residences at up to 70 mph, it was clear that keeping vibration levels below the impact threshold would be a technical and financial challenge.
As part of the EIS/EIR of the SVRT Project, ATS provided a third party, objective review of the noise and vibration analyses. Because of the close proximity of the alignment to residential areas and the high speed of the BART trains, particular attention was paid to the assumptions that influenced both the predicted vibration levels and the effectiveness of the recommended mitigation measures. One conclusion was that the projections were based on BART measurement data from early 1980s, which meant that millions of dollars of recommended mitigation might be based on outdated information.
As part of the conceptual design of the system, ATS was retained to develop a strategy for mitigating the expected impacts. The study included detailed measurements to characterize noise and vibration on the existing BART system and to determine how current mitigation measures are performing.
The study showed that the vibration velocity spectrum for the line-segment portions of this project typically will peak in the 16 to 25 Hz range. Although this makes the vibration difficult to mitigate, mitigation is feasible with “standard” measures such as heavy-weight floating slab (the expensive approach) and through innovative measures that involve stiffening the track support system with piers or a thick concrete slab.
Below are copies of the paper presented by Hugh Saurenman at the Eight International Workshop on Railway Noise in September 2004.