Use of Tunnel Vibration Monitoring to Predict Vibration in Buildings

Hugh SaurenmanATS Consulting

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Background

• University of Washington Seattle Campus, a world-class research facilities with a considerable amount of vibration sensitive equipment

• Negotiated agreement on maximum vibration levels in 24 buildings that includes potential liquidated damages (up to $100k/day!!)

• Agreement to install monitoring system in tunnel• Need to predict vibration in buildings based on

vibration in tunnel:VAE = Vibration Adjustment Estimate

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Sensitive Buildings, 24 Identified by UW

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740 ft

916 ft

840 ft

593 ft

Vibration Measurement Locations (A)

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Vibration Measurement Locations (B)

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Vibration Measurement Locations (C)

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MIA Limits (Master Implementation Agreement)

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MIA Limit vs. Ambient Vibration, UWMC

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Challenges

• Distance, 600 to 1000 ft.• Number of structures in path including parking

structure, buildings, utilities, etc.• Stakeholders have been discussing (negotiating,

arguing, …) for over 15 years.• Train vibration less than ambient inside buildings.• Vibration mitigation measures at crossover (soft

fasteners, low impact frogs).• Limited time to perform measurements and provide

results.• UW & Sound Transit needed to agree on results before

system opened.

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Testing Approach

• Multiple measurement stations with all recorders synchronized.

• When possible use data from monitoring system (8-sec rms vibration at 1-second intervals).

• Compare vibration levels during test train events with ambient immediately before and after train events.

• Impact tests of transfer mobility to supplement train vibration datao Outside to inside buildingso Tunnel to surface

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Intended Approach

• Extract level vs. distance from test train measurements

• Use impact testing to estimate outdoor-to-indoor change

• Adjust as necessary

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Actual Approach

• Extract level vs. distance from test train

• Extrapolate to buildings

• Use impact testing to estimate outdoor-to-indoor change

• Adjust as necessaryo To avoid false alarms cause by ambiento To provide realistic levels in buildings

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More on Adjustments

1. If train vibration causes apparent increase in ambient vibration, force predicted vibration at building to match train vibration.

2. When ambient vibration from traffic exceeds train vibration at low frequencies, which leads to false alarms, adjust to remove false positives.

3. If train vibration cannot be seen to change ambient, train vibration is at least:

𝐿𝐿𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑀𝑀𝑀𝑀𝑀𝑀 ≤ 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 − 10

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Comparison of Train Vibration and Traffic Vibration

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Example of Final VAEs (CHDD)

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Conclusions

• Train vibration at buildings was not measurable. Therefore we can only predict an upper bound for VAEs.

• Low frequency vibration (<10 Hz) propagates poorly from the tunnel.

• Low frequency vibration from traffic often exceeded train vibration at monitors.

• Estimated vibration in all buildings is well below the MIA limit.

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Increase in Train Vibration Required for Fault

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Lessons…

• Low frequency vibration is not an issue for U-Link.• Researchers tend to over estimate the sensitivity of

their equipment to vibration.• Low frequency vibration from traffic is often greater

than train vibration, even in the U-Link tunnel.• It is not clear how widely this observation is

applicable because of the effects of geologic conditions.

• It is critical to obtain detailed data on existing ambient vibration for future projects where interference with sensitive research equipment is an issue.

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Thank You!

Questions?