Evaluating the probability of failure of an earth dam by seismically induced liquefaction

Existing dams rarely if ever were designed to meet modern seismic safety criteria. During the past 20 years, earthquake design parameters have generally increased at all sites and now exceed the original design standards, sometimes by a significant margin. That is not to say that all dams that have not been upgraded to meet these standards will actually fail if subjected to an earthquake of present day design magnitudes and/or peak ground accelerations. The apparently continuous increase in the expected sizes of earthquakes poses the following question: ''Is it absolutely necessary to continually strengthen all dams to meet these ever increasing earthquake loading conditions?''. This paper describes the methodology to determine the probability of failure of an earth dam by liquefaction. Included is a description of the one and two dimensional analysis methods used to evaluate the extent of liquefaction, the probability of liquefaction and the probability of dam failure given liquefaction.