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Abstract

Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H.B. Seed and I.M. Idriss developed and published the basic "simplified procedure" for evaluating liquefaction resistance of soils. The procedure, which is largely empirical, evolved over the decades, primarily through summary papers by H.B. Seed and his colleagues, until it has now established itself as the the standard of practice in North America and throughout much of the world.

In 1985, Professor Robert V. Whitman convened a workshop on behalf of the National Research Council (NRC) in which thirty-six experts reviewed the state-of-knowledge and the state-of-the-art for assessing liquefaction hazard. No general review or update of the simplified procedures has occurred since that time.

The purpose of this 1996 workshop, sponsored by the National Center for Earthquake Engineering Research (NCEER), was to convene a group of experts to review developments and gain consensus for further augmentations to the procedure. To keep the workshop focused and the content tractable, the scope was limited to evaluation of liquefaction resistance. Post-liquefaction phenomena, such as soil deformation and ground failure, although equally or more important, were beyond the scope of this workshop.

The participants developed consensus recommendations on the following topics:

  • Use of the standard and cone penetration tests for evaluation of liquefaction resistance
  • Use of shear wave velocity measurements for evaluation of liquefaction resistance
  • Use of the Becker penetration test for gravelly soils
  • magnitude scaling factors
  • correction factors K1 and KaX
  • evaluation of seismic factors required for the evaluation procedure.

Probabilistic analysis and seismic energy considerations were also reviewed. Seismic energy concepts were judged to be insufficiently developed to make recommendations for engineering practice. Probabilistic methods have been used in some risk analyses, but are still outside the mainstream of standard practice.

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