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Valley Rapid Transit Project (BART Extension to San Jose)
LOCATION
San Jose, California
CLIENT
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mitigation might be based on outdated information.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.
Click here for a copy of the paper presented by Hugh Saurenman at the Eight
International Workshop on Railway Noise in September 2004.
