There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the ''simplified procedure'' for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmen- tations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommen- dations were formulated.

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Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils

A study on the influence of the plasticity index (PI) on the cyclic stress‐strain parameters of saturated soils needed for site‐response evaluations and seismic microzonation is presented. Ready‐to‐use charts are included, showing the effect of PI on the location of the modulus reduction curve G/Gmax versus cyclic shear strain γc, and on the material damping ratio λ versus γc curve. The charts are based on experimental data from 16 publications encompassing normally and overconsolidated clays (OCR=1-15), as well as sands. It is shown that PI is the main factor controlling G/Gmax and λ for a wide variety of soils; if for a given γc PI increases, G/Gmax rises and λ is reduced. Similar evidence is presented showing the influence of PI on the rate of modulus degradation with the number of cycles in normally consolidated clays. It is concluded that soils with higher plasticity tend to have a more linear cyclic stress‐strain response at small strains and to degrade less at larger γc than soils with a lower PI. ...

Effect of Soil Plasticity on Cyclic Response

Two aspects of seismically-induced liquefaction are discussed which are of vital engineering significance: the triggering condition and the consequences of liquefaction. The triggering condition is examined with respect to liquefaction analysis, note being taken of the onset condition which is governed by cyclic strength. Consequences of liquefaction are discussed with respect to post-seismic stability analysis, in which the residual strength plays a major role. Procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced, and the applicability of this method for estimating associated ground settlements is discussed. The evaluation of residual strength requires a better understanding of undrained sand behaviour. Results of extensive laboratory rests on Japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better. The results of laboratory tests on silty sands are examined in the same way. AH the results are...

Liquefaction and flow failure during earthquakes.

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=5754&context=engpapers

Guidelines for landslide susceptibility, hazard and risk zoning for land-use planning

Significant factors affecting the liquefaction (or cyclic mobility) potential of sands during earthquakes are identified, and a simplified procedure for evaluating liquefaction potential which will take these factors into account is presented Available field data concerning the liquefaction or nonliquefaction behavior of sands during earthquakes is assembled and compared with evaluations of performance using the simplified procedure It is suggested that even the limited available field data can provide a useful guide to the probable performance of other sand deposits, that the proposed method of presenting the data provides a useful framework for evaluating past experiences of sand liquefaction during earthquakes and that the simplified evaluation procedure provides a reasonably good means for extending previous field observations to new situations When greater accuracy is justified, the simplified liquefaction evaluation procedure can readily be supplemented by test data on particular soils or by ground response analyses to provide more definitive evaluations

Simplified procedure for evaluating soil liquefaction potential

Data are presented concerning the shear modulus and damping ratios of sands and gravelly soils as determined by laboratory and field tests. A simple relationship is proposed to relate the shear modulus of a cohesionless soil to a modulus stiffness coefficient, which is a soil property and depends on the characteristics of the soil, and the effective mean principal stress at any point in the soil. Values for the modulus coefficient at low strains are suggested, and it is shown that these values for sands can be estimated from the standard penetration resistance of the sand. Values for gravels are generally greater than those for sands by factors ranging from 1.35–2.5. Suggestions are also made for determining the variation of shear modulus with shear strain and the damping ratios for both sandy and gravelly soils.

Moduli and Damping Factors for Dynamic Analyses of Cohesionless Soils

The evolution of a simplified procedure for evaluating the liquefaction potential of sand deposits using data obtained from standard penetration tests is reviewed. Field data for sites which are known to have liquefied or not liquefied during earthquakes in the United States, Japan, China, Guatemala, Argentina, and other countries are presented to establish a criterion for evaluating the liquefaction potential of sands in Magnitude 7‐1/2 earthquakes. The results of this study are then extended to other magnitude earthquakes using a combination of laboratory and field data. Available information on the liquefaction resistance of silty sands is also reviewed and a simple procedure for considering the influence of silt content is proposed. A method is presented for using the field data to evaluate the possible magnitude of pore water pressure generation in sands and silty sands which remain stable during earthquake shaking. Finally, the applicability of other in situ field tests, such as the static cone pene...

Izzat M. Idriss

Papers

Simplified procedure for evaluating soil liquefaction potential

Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils

Moduli and Damping Factors for Dynamic Analyses of Cohesionless Soils

Evaluation of Liquefaction Potential Using Field Performance Data

Semi-empirical procedures for evaluating liquefaction potential during earthquakes