Calculation of the seismic risk of an earth dam susceptible to liquefaction

This paper describes B.C. Hydro's most recent efforts to develop a credible and defensible analysis technique for dam safety decisions concerning seismically induced liquefaction. The work outlined herein is an improvement on the previously reported methodology (Hartford et al., 1997) which relied on slope stability methods to form the link between liquefaction triggering and deformation/damage of the dam. While the event tree structure is essentially the same as that reported previously, the slope stability approach proved to be unsatisfactory and this paper presents a deformation analysis approach to estimating the probability of breach/damage given liquefaction triggering. The paper identifies areas where available deterministic analysis techniques may not be sufficiently "well tuned" for adherence to the strict rules of probabilistic analysis. The paper also describes approximations in the approach to the probabilistic component necessary to make the analysis tractable. The paper demonstrates that despite these weaknesses in modern dam analysis and risk analysis practices, it is still possible to work towards a pragmatic interpretation of the outputs of these analyses and to complete a detailed probabilistic risk analysis for input into important and difficult risk-based decision-making processes.