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 specimen preparation procedure is presented that offers an improved method of preparing reconstituted sand specimens for cyclic triaxial testing. The method leads to more consistent and repeatable test results. This procedure (1) minimizes particle segregation, (2) can be used for compacting most types of sands having a wide range in relative densities, and (3) permits determination of the optimum cyclic strength of a given sand at a given dry unit weight.

Preparing Test Specimens Using Undercompaction

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Seismic design and analysis of underground structures

Preface Acknowledgements 1. Introduction 2. Atmospheric structure, composition and thermodynamics 3. The continuity and thermodynamic energy equations 4. The momentum equation in Cartesian and spherical coordinates 5. Vertical-coordinate conversions 6. Numerical solutions to partial differential equations 7. Finite-differencing the equations of atmospheric dynamics 8. Boundary-layer and surface processes 9. Radiative energy transfer 10. Gas-phase species, chemical reactions and reaction rates 11. Urban, free-tropospheric and stratospheric chemistry 12. Methods of solving chemical ordinary differential equations 13. Particle components, size distributions and size structures 14. Aerosol emission and nucleation 15. Coagulation 16. Condensation, evaporation, deposition and sublimation 17. Chemical equilibrium and dissolution processes 18. Cloud thermodynamics and dynamics 19. Irreversible aqueous chemistry 20. Sedimentation, dry deposition and air-sea exchange 21. Model design, application and testing Appendix A. Conversions and constants Appendix B. Tables References Index.

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Fundamentals of atmospheric modeling

PART 1 DEALS WITH THE DYNAMIC ASPECTS OF THE SUBJECT: MATHEMATICAL ANALYSIS OF SYSTEMS SUBJECTED TO INDEPENDENT VIBRATIONS BY MEANS OF MATHEMATICAL MODELS. THE ANALYTICAL SYSTEMS USED ARE NON-LINEAR SYSTEMS, HYDRODYNAMICS AND NUMERICAL METHODS. PART 2 EXAMINES SEISMIC MOVEMENTS, THE DYNAMIC BEHAVIOUR OF STRUCTURES AND THE BASIC CONCEPTS OF THE SEISMIC DESIGN OF STRUCTURES.

Fundamentals of earthquake engineering

The important factors affecting the dynamic response of saturated sand layers to earthquake motions are: (1)The initial shear modulus in situ; (2)the variation of shear modulus with shear strain; (3)contemporaneous generation and dissipation of pore-water pressures; (4)changes in effective mean normal stress; (5)damping; and (6)hardening. Constitutive relations are formulated that take all these factors into account and these are incorporated into a nonlinear method for the dynamic effective stress analysis of saturated sands. The method predicts the phenomenological features of the dynamic response of saturated sand layers that commonly occur as the pore-water pressure rises in the sand during earthquake shaking. It allows the distribution of pore-water pressure and the effects that drainage and internal flow have on the location and time of liquefaction to be determined quantitatively.

An Effective Stress Model for Liquefaction

The resistance of a saturated sand to liquefaction under cyclic loading has been assumed to depend only on the void ratio, effective stress system and intensity of cyclic loading. The effect of strain history on the resistance to liquefaction is investigated here by means of triaxial and simple shear tests. The resistance of a saturated sand to liquefaction as measured in laboratory tests is very much influenced by the previous strain history. Partial liquefaction which occurs at small shear strains greatly increases the resistance to liquefaction in subsequent tests. Cycles of large shear strains, or quasi-static shear strains > 7.5%, reduces the resistance to liquefaction. The increase in resistance to liquefaction created by a very small shear strain may result from the elimination of small local instabilities in the original sand structure. The loss of resistance caused by larger shear strains is thought to be due to either the creation of a uniform metastable structure or the development of a nonuniform structure.

Effect of strain history on liquefaction of sand

Data from cyclic loading simple shear and triaxial tests indicate that the important variable controlling the incidence of liquefaction in a given number of cycles in a saturated sand at a particular void ratio is the initial effective stress ratio; the ratio of the peak alternating shear stress to the initial effective mean normal stress. Contrary to previously published results, equal resistances to liquefaction are obtained in both kinds of tests. This agreement is considered to be due to three things: (1) Representation of the confining pressure in the simple shear test by the mean normal stress in the plane of deformation; (2) the improved model of the simple shear apparatus used; and (3) the use of experimental techniques which insures the development of uniform strains in the simple shear test. The experimental techniques used evolved from a fundamental study of the deformation of samples in the simple shear apparatus.

W. D. Liam Finn

Papers

An Effective Stress Model for Liquefaction

Effect of strain history on liquefaction of sand

Sand Liquefaction in Triaxial and Simple Shear Tests

Seismic Design Guidelines For Port Structures

Finite elements incorporating characteristics for one-dimensional diffusion-convection equation