Evaluation of Earthquake-Induced Liquefaction Damage Potential to Infrastructure

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

The recent earthquakes in New Zealand, Chile, and Japan highlight the damaging effects of earthquake-induced liquefaction on both the natural and built environments. For example the 2010-2011 Canterbury, New Zealand, earthquake sequence resulted in approximately $35 billion in damage to buried utilities, roads, buildings, and other infrastructure in Christchurch, with much of the damage being a direct consequence of liquefaction. "Turning disaster into knowledge," this award supports the development of a framework to assess liquefaction damage potential on infrastructure using the wealth of field performance data from the recent earthquakes, as well as data from well-documented historic liquefaction case histories and supplemental computer simulations. This research project is motivated by the need to properly account for triggering and damage within a framework that respects their fundamental differences, systematically classifies the severity of liquefaction and relates it to the response of the entire soil profile, removes much of the subjectivity in interpreting liquefaction case histories used to develop triggering curves, and avoids the double counting of factors that influence liquefaction damage potential. The results of this award will help minimize losses from earthquakes by improving the current methods for liquefaction risk assessment. Furthermore, the educational impacts will not only result from the increased technical understanding of the subject matter, but will also result from the international collaborations with colleagues in New Zealand, Chile, and Japan. The distinction between liquefaction triggering and the resulting damage is blurred by subjectivity in current approaches used to develop liquefaction "triggering" curves. The reason for this is that liquefaction "triggering" curves are primarily based on observed severity of surface manifestation data. As a result, the purported simplified liquefaction "triggering" curves are actually combined "triggering" and "surface manifestation" curves. Consequently, the use of these curves within current liquefaction damage potential index frameworks inherently double counts factors that influence liquefaction damage potential. This is particularly an issue for reliably assessing the risk due to liquefaction. This award supports the development of a liquefaction triggering curve and damage potential index within a consistent framework that provides a clear separation and proper accounting of liquefaction triggering and liquefaction damage potential. Most notably, this framework avoids the need to tie liquefaction occurrence to a specific layer within a profile; instead, this framework integrates information from the entire profile for each case history. The classification of manifestation severity will follow a detailed rubric such that a unified and objective approach for liquefaction hazard assessment is formed. The field performance data will be analyzed using the Bayesian updating technique to develop a probabilistically based "true" liquefaction triggering curve. This technique will also be used to determine the damage potential index values that correspond to different probabilities of liquefaction severity, where liquefaction severity is used as a proxy for damage potential. However, this framework will preserve the elegance and simplicity of the simplified liquefaction triggering evaluation procedure and Liquefaction Potential Index formulation because of their familiarity to practicing engineers.