Seymour Falls Dam Seismic Upgrade

ACEC Award of Excellence

The Seymour Falls Dam is a key component in the water supply for the Greater Vancouver region. It is a composite structure consisting of a slab and buttress concrete section, an earthfill embankment and an extensive impervious upstream blanket. The dam was constructed in 1961 to a height of 30 m, with provision for future raising of 17.4 m. Even though the dam was in excellent condition after 40 years of service, it did not meet new criteria for earthquake safety.

 

“A particular challenge was the explosive compaction, detonating a total of over 33,000 kg of explosives at the toe of a fully operational water reservoir on a liquefiable foundation. Every blast was carefully checked and re-checked before detonation.”

-Neil Singh, Resident Engineer

Challenges

  • Concrete and earthfill sections were considered potentially unstable under a maximum credible earthquake with up to 0.5 g peak ground acceleration.
  • Loose, liquefiable fan deposits in the dam foundations
  • Existing dam and reservoir had to remain fully functional during construction to provide water supply to Greater Vancouver.
  • A major earthquake could significantly increase seepage beneath the dam in the event of disruption of the impervious lining on the bottom of the reservoir.

Solutions

  • Preliminary designs and capital cost estimates for remedial works, and design for the rehabilitation of the dam’s earthfill portion
  • Foundation densification was undertaken between upstream berm and downstream toe of earthfill section to prevent liquefaction shear failure
  • In-situ densification achieved with a combination of explosive and dynamic compaction
  • Cable anchors and continuously reinforced concrete shear walls stabilize the slab and buttress dam
  • New internal drainage zones with pressure relief wells were installed after the foundation soils were densified.

Successes

  • New earthfill dam constructed on the new earthquake resistant foundation, tied into the core of the existing dam and connected to the concrete dam by means of an extension to the concrete gravity transition block
  • Reservoir remained in service throughout the construction period
  • The new earthfill and concrete structure is meets safety requirements, both Provincial and industry standards.

Papers:

Elliott, R.J., B. Gohl, N.K. Singh and F. Huber. 2009. “Explosive Compaction of Foundation Soils for the Seismic Upgrade of the Seymour Falls Dam,” in: 35th Annual Conference on Explosives and Blasting Technique, Denver, Colorado, February 8-11, 2009. Cleveland, Ohio: International Society of Explosives Engineers.

Thavaraj, T., L. Murray, N. Singh, F. Huber and M. Gant. 2012. “Seismic Deformation Analyses of Seymour Falls Dam,” in: GeoManitoba, Building on the Past, 65th Canadian Geotechnical Conference, Winnipeg, Manitoba, September 30-October 3, 2012. Toronto: Canadian Geotechnical Society.

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