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Lafayette Reservoir Outlet Tower Seismic Retrofit Project - EBMUD


Key Features 


  • 170-foot high, reinforced concrete Outlet Tower built in 1927 extending 43 feet below grade, serving as the dam’s inlet/outlet conduit and housing the overflow spillway for the reservoir

  • Design and assessment of various retrofit alternatives for the Outlet Tower to address seismic, mechanical and electrical deficiencies


Geotechnical Challenges 


  • Compilation and review of pre-existing geotechnical reports, historical maps and drawings to assess data gaps and investigation requirements

  • Over-water 120-foot-deep geotechnical boring, soil sampling, bedrock coring and down-hole geophysical suspension logging in close vicinity of underground dam’s inlet/outlet conduits

  • Complying with CDFW environmental and permit requirements


Innovative Solutions


  • Assessment of seismic retrofit alternatives such as: through-wall post tensioning, external fiber wrapping, and tower shortening

  • Use of geophysical surveying to obtain shear wave velocity (Vs) measurements down to 100 feet below the bottom of the reservoir

  • Use of a barge-mounted rotary wash drill rig with sealed drill fluid system, operating with a “Tier Two” diesel engine and environmentally friendly “Clarity” (mineral) hydraulic oil

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