Questions/Inquiries
e-mail Sarah Berry Cook @
skberry@u.washington.edu
Conference Chair
Steve Kramer
University of Washington
Civil Engineering Dept.
Box 352700
Seattle WA 98195
kramer@u.washington.edu
Conference Management
Engineering Professional Programs
University of Washington
3201 Fremont Ave N
Seattle WA 98103-8866
tel: 206.543.5539
attn: Sarah Berry Cook @
skberry@u.washington.edu
| Invited Speakers |
The conference will feature an outstanding group of invited speakers, all of whom are internationally recognized as leading experts in their individual fields. These speakers have been asked to prepare "emerging art" papers and presentations that focus on developments in important technical areas within the past 10 years and on anticipated developments in the next 10 years. This innovative approach promises to produce a tremendous amount of up-to-date, useful information with a wide range of applications in geotechnical engineering practice.
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Post-Triggering Response of Liquefied Soil in the Free Field and Near Foundations
Ricardo Dobry
The paper focusses on the post-triggering behavior of liquefied soil and its implications for evaluations of the engineering effects of liquefaction. While new tools and refinements have been developed, and some important problems still remain, triggering of liquefaction is generally well understood and reliable evaluation methods exist. On the other hand, the basic nature and characteristics of the liquefied soil after triggering - which determine most of the engineering effects of liquefaction - are complex and remain poorly understood. The paper reviews some of the evidence from the field, and centrifuge shaking experiments, as well as its implications for the modeling and evaluation of liquefaction effects. The different behavior of lateral spreads versus flow slides is emphasized. The importance of soil layering in the free field and as a factor determining damage to pile foundations is discussed in some detail.
Seismic Safety of Embankment Dams Developments in Research and Practice 1988-1998
W.D. Liam Finn
Developments in the procedures for evaluating the seismic response and safety of embankment dams since the last decennial conference, Earthquake Engineering and Soil Dynamics II, in 1988 are reviewed. There are three major developments. First is the extensive research on the factors controlling the residual strength of potentially liquefiable sands and the selection of strengths for use in design. The second is the use of displacement as a criterion for assessing the seismic performance of embankment dams and planning remediation measures, especially when there is a potential for liquefaction in the dam itself or in the foundation. This requires large strain analysis. The third development is the emergence of seismic risk and reliability analysis as an aid to determining the dominant failure modes of the dam, the probability of occurrence of unacceptable damage, and the associated probabilities of both economic losses and loss of life.
Recent Trends and Future Prospects in Seismic Hazard Analysis
Arthur Frankel and Erdal Safak
Over the past fifteen years or so, probabilistic seismic hazard analysis (PSHA) has undergone a transformation from a process based mainly on seismological input to an integration of geophysical, geological, and seismological information. Recent studies have focused on characterizing the uncertainties in the input data (sources and .ground motions) and differences in interpretation by using alternative models, logic trees, and Monte Carlo simulations. In the western U.S., geologic slip rates and paleoseismic information for faults have been used to estimate earthquake recurrence times on faults for hazard assessment. In the Central and Eastern U.S. (CEUS), dating of paleoliquefaction associated with large prehistoric earthquakes has been critical for assessing hazard. A global characterization of seismicity- of rifted continental margins has been useful for delineating hazard in the CEUS. There is a trend of using- the spatially-smoothed historical. seismicity directly as one model of future seismicity, in- addition to a real source zones. In the near-future, detailed seismic hazard maps incorporating site response will be produced for high seismic risk urban areas. Future improvements will be the application- of new, measures of ground motions in hazard analysis which include duration information and near-field effects such as pulses of ground motion from directivity. One key frontier is the use of entire time histories in PSHA, including 3-D basin effects and nonlinear site response. These improvements can be incorporated into performance-based design. We propose a method to directly use earthquake time histories in probabilistic assessments of building damage. The display of seismic hazard in terms of magnitude and distance contributions (de-aggregation) has become an important tool for specifying design earthquakes. Future frontiers in source characterization include a better understanding of earthquake recurrence on faults, time-dependent hazard based on the time of the previous event on a fault, the relationship between geodetically-measured deformation and long-term seismicity rate, earthquake clustering in time and space, and stress changes from large earthquakes that can affect earthquake occurrence on surrounding faults.
Seismic Soil-Structure Interaction: New Evidence and Emerging Issues
George Gazetas & George Mylonakis
Key phenomena associated with the seismic interplay between soil, foundation, and structure are introduced and the available methods briefly explained. Emphasis is given to deep foundations (piles and caissons), but a comprehensive review of the subject is beyond our scope. Instead, we have chosen for discussion five special topics which satisfy one or both of the following criteria : new field evidence on their significance has accumulated ; renewed practical interest has been demonstrated.
Specifically : (a) The role of dynamic soil-structure interaction (SSI) on the response of pile-suppported structures is re-explored, and the failure of Hanshin Expressway Route 3 in Kobe (1995) is analysed to show the detrimental role of SSI on the fatal behavior of the bridge. This and additional similar evidence contradict the currently prevailing fallacy in structural engineering for the "beneficial" role of SSI. (b) For the kinematic distress of piles (under stable soil conditions) recent solutions are outlined and validated through two case histories involving actual measurements of bending strains. Among the unresolved issues : modeling large deformations of the surrounding soil due to lateral spreading or other instabilities. Caisson-type foundations have resisted successfully, and in fact restricted, such large deformations. (c) Pile-to-pile interaction under dynamic loading has a substantial effect on the stiffness of a large group of piles. The response of such groups can practically be obtained with the superposition method using simplified analytically-expressed interaction factors between two piles. The sensitivity of such factors to soil layering and soil nonlinearity complicates the task, as illustrated with examples from the recent literature. (d) Inclined piles had suffered disproportionately in earthquakes of the past and their seismic role has been widely viewed as detrimental; their use has been discouraged in seismic regulations. New theoreical work and some recent field evidence strongly suggest that the opposite may be the case. (e) The issue of structural yielding and inelastic bending of piles is being explored. Such action may be practically unavoidable (especially under bridge piers) and, in fact, it may not be detrimental; but its consequences on the overall ductility demand imposed to the pier cannot presently be readily assessed.
The aim of the paper is not to provide complete solutions to these problems but only to highlight the issues, outline new results or field evidence, and raise the questions of practical significance.
Seismic Analysis and Performance of Retaining Structures
Susumu Iai
Many of the assumptions made in the conventional sliding block approach, successfully applied to retaining walls with dry soil, become questionable when the soil is submerged. Adequate characterization of the undrained behavior of sand under transient and cyclic loads is needed for reliable and economical design of waterfront retaining structures. This paper discusses how the undrained behavior of sand affects the deformation/failure mode and degree of deformation of the waterfront retaining structures, through an effective stress analysis based on recent case histories during earthquakes. The retaining structures discussed include gravity and sheet pile walls, and a pile-supported wharf.
An Overview of the Current and Emerging State of the Art of Site Response During Earthquakes
I.M. Idriss
Site response analyses are influenced by input motion, by the characteristics
the site (including layering and dynamic properties) and by the method of
analysis. These three factors are examined, in this paper, in terms of the
current state of the art and what appears to be the emerging state of the
art for each. The increase in available case histories that are most relevant
to assessing site response (e.g., downhole arrays; centrifuge tests; large
shaking table tests) is providing the means to examine these three factors
far more carefully than had been possible in the past. These examinations
will lead to improved means for assessing site response during earthquakes.
Problems Associated with Liquefaction and Lateral Spreading During Earthquakes
Kenji Ishihara and Misko Cubrinovski
New problems arising from liquefaction and lateral spreading during recent large earthquakes are addressed with some preliminary thoughts and suggestions. First, importance is stressed for dynamic property characterization of soils having wide range of grain composition such as gravel-containing silty sands. Second, uncertainty and lack of information are pointed out regarding correlations between in-situ measured parameters and laboratory-determined soil properties on undisturbed samples. Thus there are needs to fill the gap of knowledge concerning the link between these two kinds of parameters. Third, great interest has been kindled for performances of piles subjected to lateral spreading of the ground. The soil-pile interaction in the course of large soil deformation has been recognized as an issue of considerable importance in relation to renovation in the design philosophy and its practice. Somewhat detailed account on the above three unexplored areas is given in this paper.
Design Considerations in Ground Improvement for Seismic Risk Mitigation
James K. Mitchell, Harry G. Cooke , and Jennifer A. Schaeffer
Several types of ground improvement have been used extensively for mitigation of earthquake-induced liquefaction and lateral spreading, and new methods and strategies for site remediation are continually being developed. From experiences in several earthquakes in Japan, especially the 1995 earthquake in Kobe, and in the U.S., especially the 1989 Loma Prieta earthquake, it is known that these methods are effective in preventing or significantly reducing ground deformations and damage to structures and facilities. In this paper, ground improvement methods are summarized in two categories; namely, those best suited for use at large, open, undeveloped sites, and those most suitable for constrained or developed sites. Several anticipated or needed future developments in the design of ground improvement projects and in the execution of the methods themselves are noted. A general approach to the design of ground improvement for a specific site is outlined. Several uncertainties which impact the design and performance prediction are reviewed, including the effect -of ground treatment on ground motions, pore pressure plume migration, forces exerted on improved ground and structures by liquefied soil, soil-structure interaction, and the impacts of these issues on the analysis of stability and deformation of treated ground. Studies that address these problems are described briefly, and some tentative design recommendations are given.
An Overview of Geotechnical and Lifeline Earthquake Engineering
T.D. O'Rourke
This paper presents an overview of lifeline systems and geotechnical earthquake hazards. Sources of permanent ground deformation (PGD) are reviewed with reference to recent North American and Japanese eart