david cole, dowl engineers may 1, 2008 -...
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David Cole, DOWL EngineersMay 1, 2008
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• Produced by Harding Lawson Associates, 1979
• Geotechnical Hazards Assessment Study
• Based on:o Geologic maps and soil data available at the time
o Effects of 1964 earthquake
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• Similar to 1964 earthquakeo Subduction zone evento M ≈ 9
• Return period not consideredo “Worst Case” event
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• No estimate of amount of ground displacement.
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New Ground Failure MapNew Ground Failure Map(2% probability in 50 years)(2% probability in 50 years)
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• LIDAR Mapping of Anchorage (5 ft cells)
• Geologic Map of Anchorage (USGS/DGGS)
• Two Ground Failure Maps ProducedoUSGS, P(E) = 10% in 50 years, PGA ≈ 0.43g
oUSGS, P(E) = 2% in 50 years, PGA ≈ 0.69g
• Newmark Slope Displacement Model
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• Rigid Block Slides on an Inclined Plane
αD f= f(a)
R f
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• Block has a known “critical” or yield acceleration (acrit) where the inertial forces developed in the block (Df) exceed the shear strength of the soil, (Rf)
• The analysis calculates the cumulative down-slope movement of the block as the critical acceleration is overcome by the ground shaking
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• Double integration of a ground acceleration record is conducted to determine the cumulative down-slope movement
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• The deep translational slide areas shown on the new map are based on the areas shown on the old map.
• No additional work was performed to evaluate the areas that could be affected or the amount of ground displacement.
• No estimate of lateral displacement included
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New Ground Failure MapNew Ground Failure Map(P(E) = 2% probability in 50 years)(P(E) = 2% probability in 50 years)
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Current Ground Failure MapCurrent Ground Failure Map
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Questions?Questions?