Practical Studies of the Seismic Response of a Rockfill Dam and a Tailings Impoundment

Two case studies from engineering practice are presented to demonstrate how useful a sophisticated finite element analysis can be in providing a comprehensive understanding of how dams behave during earthquakes. The first example involves determining, from the recorded performance of a rockfill dam, the volume change characteristics of the rockfill which cannot be measured directly. The second example covers the full range of current capability for analysis. It involves dynamic effective stress analysis of a tailings dam to check the triggering of liquefaction and the analysis of post-liquefaction flow deformations

Assessment of Liquefaction Potential and Post-Liquefaction Behavior of Earth Structures: Developments 1981-1991

Significant developments in procedures for evaluating liquefaction potential and the post-liquefaction behaviour of earth structures are reviewed for the period 1981-1991. Particular attention is paid to the re-valuation of the liquefaction induced slide in the San Fernando Dam following the 1971 earthquake. The findings of this study have had a major impact on engineering practice

Estimating Post-Liquefaction Displacements in Embankment Dams and Priorities Remediation Measures

Large displacement analysis is used to simulate the failures of flood protection dikes in Hokkaido, Japan, which occurred during the 1993 Kushiro-oki earthquake. These studies served to validate the method of analysis. The analysis was then used to predict displacements in dikes with potential for liquefaction by relating displacements to geometric characteristics of the dikes: height, slopes, and thickness of potentially liquefiable layer. The predictions were verified using dike displacement data from the Nansei-oki earthquake of 1994. The basis for reliable post-liquefaction analysis is a good estimate of the residual strength of the liquefied soils. For this reason, recent developments in evaluating residual strength are reviewed

Case Histories in Seismic Response Analysis

The reliability and utility of dynamic response analysis in geotechnical engineering is explored by a series of case histories. A detailed study of the seismic response of Mexico City sites during the 1985 earthquake shows clearly the limitations of present methods for estimating the appropriate input motions for analysis and the necessity of using a suite of representative input motions. Analyses of seismic soil-structure interaction are conducted on centrifuged models subjected to simulated earthquake loading. Finally the seismic response of a tailings dam is investigated using nonlinear dynamic effective stress analysis

The Impact of Low Probability Ground Motions on Canadian Geotechnical Engineering Practice

The adoption of design motions with a 2% rate of exceedance in 50 years in the National Building Code of Canada (NBCC 2005) has had a major impact on geotechnical engineering practice in Canada. The peak ground accelerations were doubled compared with the previous motions which had an exceedance rate of 10% in 50 years. The increase in accelerations has had a huge effect on assessments of liquefaction potential and slope stability, because the methods of assessment in common use depend on peak ground acceleration. This paper describes typical problems encountered in Canadian practice with use of the low probability motions and describes some measures for alleviating the impact on design, while maintaining the code objective of life safety

Deep Foundations in Liquefiable Soils: Case Histories, Centrifuge Tests and Methods of Analysis

This paper describes the performance of pile foundations in liquefied soils. Two different aspects of pile response are considered, seismic response to earthquake shaking and response to lateral spreading when the liquefied ground is sloping. The case histories show that piles can be designed economically to resist large lateral displacements and that most of the reported examples of damage from lateral spreading involve weak piles with little reinforcement which were installed to control vertical settlements and were not designed to be moment resistant. A quasi-3-D continuum method is presented for dynamic effective stress response analysis of pile groups in liquefiable soils. The method is validated using data from centrifuge tests. Methods are presented also for the analysis of piles due to lateral spreading

Keynote Lecture: Some Recent Developments in the Selection of Ground Motions for Design

This paper describes some recent developments in the selection of ground motions for design; the conditional mean spectrum approach and risk targeted ground motions. The conditional mean spectrum approach is just finding its way into practice and its application to a major dam is presented. Risk targeted ground motions are the basis for the next generation of building codes in the USA. The process of determining these motions is explained. Finally in the context of the retrofit of 800 schools in British Columbia, Canada, a performance based design procedure based on incremental dynamic analysis (IDA), with direct application to geotechnical earthquake engineering is presented. An interesting feature of this method is the segregation of hazard into subduction, sub-crustal and crustal earthquakes and the calculation of risk for each type independently and combining these risk components to obtain the total risk of violating the performance criterion