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Proceedings of a workshop on Seismic Performance and Simulation of Pile Foundations in Liquefied and Laterally Spreading Ground, held in Davis, California, March 16-18, 2005. Sponsored by the Pacific Earthquake Engineering Research Center; University of California at Berkeley; Center for Urban Earthquake Engineering; Tokyo Institute of Technology; Geo-Institute of ASCE. This collection contains 25 papers that discuss physical measurements and observations from earthquake case histories, field tests in blast-liquefied ground, dynamic centrifuge model studies, and large-scale shaking table studies. Papers contain recent findings on fundamental soil-pile interaction mechanisms, numerical analysis methods, and reviews and evaluations of existing and emerging design methodologies. This proceeding provides comprehensive coverage of a major issue in earthquake engineering practice and hazard mitigation efforts.

Proceedings of Geo-Frontiers 2005, held in Austin, Texas, January 24-26, 2005. Sponsored by the Geo-Institute of ASCE. This Geotechnical Special Publication contains 34 papers on earthquake engineering and soil dynamics. Topics include: advances in earthquake engineering through the experimental capabilities of the George E. Brown, Jr. Network for Earthquake Engineering Simulation; geophysics; impact of liquefaction on stability of geo-structures; liquefaction evaluation and mitigation for performance-based earthquake engineering; soil liquefaction; and seismic analysis and design of MSE walls.

Nonlinear dynamic analyses using the finite element (FE) method are compared to the results of dynamic centrifuge model tests of pile-supported structures in liquefying sand profiles. The FE models utilized soil spring elements that connect pile elements to one- or two-dimensional meshes of a soil profile. Development and implementation of the soil spring materials models in the OpenSees FE platform are described. Single element examples are used to illustrate the behavior of the soil and soil spring material models. Comparisons of FE analysis to centrifuge test data of pile-supported structures in liquefying sand profiles suggest that these FE methods can reasonably approximate the essential features of soil and structural response.

Down-drag loads on pile foundations can be an important design consideration when earthquake-induced liquefaction is expected to cause ground settlements. A modified neutral plane solution for liquefaction-induced down-drag on vertical piles is described that accounts for the variation in excess pore pressures and ground settlements over time as a liquefied layer reconsolidates, the dependence of sand compressibility on excess pore pressure ratio, and the dependence of shaft skin friction on the excess pore pressure ratio. A worked example illustrates the role of various parameters on peak pile loads and settlements. The modified solution predicts substantially smaller pile settlements than obtained from a traditional neutral plane solution for end-of-consolidation conditions. Recommendations for design practice are presented.

The authors’ study provides valuable insight into the stress-strain behavior of fine-grained soils silts and clays under monotonic and cyclic undrained loading. The distinct behavioral features of sands versus clays under the aforementioned types of loading are first identified with regard to the shape of the hysteresis loops, the value of excess pore-water pressure ratio, and the magnitude of developed strains. Then, a classification of fine-grained soils into two classes of materials is proposed, namely, “sand-like” materials that are susceptible to liquefaction in the classical meaning of the term , and “clay-like” materials that are susceptible to cyclic softening. In addition, the authors emphasize the critical importance of using the appropriate procedure for evaluating the cyclic strength for each class of material. Following the establishment of the above framework, the authors review a database of test results compiled from the literature and found that the plasticity index, PI, of fines is the single most important parameter for distinguishing between the two types of behavior. They propose the use of a limit value of PI 7 as follows: 1. for PI 7, the material is susceptible to liquefaction i.e., exhibits “sand-like” behavior and its liquefaction resistance should be evaluated using the available procedures for sands; 2. for PI 7, the soil behaves as a ‘clay-like’ material and its behavior should be analyzed using the procedures available for evaluating the cyclic strength of cohesive soils. A transition zone of plasticity index from 3 to 8 is proposed by the authors, who also suggest discontinuing the use of the Chinese criteria of liquefaction susceptibility. Finally, the authors discuss the applicability of the liquefaction criterion proposed in the paper to soils containing less than 50% fines coarse-grained materials . They argue that as long as the amount of fines is greater than a threshold value, FCthr which is the limit above which the fine grains constitute the loading-carrying matrix of soil , their criterion could be extended to fines content FC 50%. The discussers have recently presented results of cyclic triaxial tests on saturated mixtures of sand with different amounts of nonplastic silt Xenaki and Athanasopoulos 2003 . The tests were conducted to investigate the effect of fines content on the liquefaction resistance of sand-silt mixtures. In view of the authors’ study and other recently published data, the discussers would like to present some related data not included in their previous publication and compare them to the findings reported in the paper.

Working Group 34 was formed by the International Navigation Association ‘‘to focus international attention on the devastating effects of earthquakes on port facilities.’’ The Working Group subsequently prepared this book of seismic design guidelines with the hope that it would have broad international support and, through continued revisions, will contribute to mitigating seismic disasters in ports worldwide.