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Dec. 21, 2016

FOR IMMEDIATE RELEASE

Report Calls for Improved Methods to Assess Earthquake-Caused Soil Liquefaction

WASHINGTON – Several strong earthquakes around the world have resulted in a phenomenon called soil liquefaction, the seismic generation of excess porewater pressures and softening of granular soils, often to the point that they may not be able to support the foundations of buildings and other infrastructure. The November 2016 earthquake in New Zealand, for example, resulted in liquefaction that caused serious damage to the Port of Wellington, which contributes approximately $1.75 billion to the country’s annual GDP. An estimated 40 percent of the U.S. is subject to ground motions severe enough to cause liquefaction and associated damage to infrastructure.

Effectively engineering infrastructure to protect life and to mitigate the economic, environmental, and social impacts of liquefaction requires the ability to accurately assess the likelihood of liquefaction and its consequences. A new report by the National Academies of Sciences, Engineering, and Medicine evaluates existing field, laboratory, physical model, and analytical methods for assessing liquefaction and its consequences, and recommends how to account for and reduce the uncertainties associated with the use of these methods.

When liquefaction occurs, wet granular materials such as sands and some silts and gravels can behave in a manner similar to a liquid. The most commonly used approaches to estimate the likelihood of liquefaction are empirical case-history-based methods initially developed more than 45 years ago. Since then, variations to these methods have been suggested based not only on case historical data but also informed by laboratory and physical model tests and numerical analyses.   Many of the variations are in use, but there is no consensus regarding their accuracy. As a result, infrastructure design often incurs additional costs to provide the desired confidence that the effects of liquefaction are properly mitigated.

The report evaluates existing methods for assessing the potential consequences of liquefaction, which are not as mature as those for assessing the likelihood of liquefaction occurring. Improved understanding of the consequences of liquefaction will become more important as earthquake engineering moves more toward performance-based design.

“The engineering community wrestles with the differences among the various approaches used to predict what triggers liquefaction and to forecast its consequences,” said Edward Kavazanjian, Ira A. Fulton Professor of Geotechnical Engineering and Regents' Professor at Arizona State University and chair of the committee that conducted the study and wrote the report. “It’s important for the geotechnical earthquake engineering community to consider new, more robust methods to assess the potential impacts of liquefaction.”

The committee called for greater use of principles of geology, seismology, and soil mechanics to improve the geotechnical understanding of case histories, project sites, and the likelihood and consequences of liquefaction. The committee also emphasized the need for explicit consideration of the uncertainties associated with data used in assessments as well as the uncertainties in the assessment procedures.

The report recommends establishing standardized and publicly accessible databases of liquefaction case histories that could be used to develop and validate methods for assessing liquefaction and its consequences. Further, the committee suggested establishing observatories for gathering data before, during, and after an earthquake at sites with a high likelihood of liquefaction. This would allow better understanding of the processes of liquefaction and the characteristics and behavior of the soils that liquefied. Data from these sites could be used to develop and validate assessment procedures.

The study was sponsored by the Bureau of Reclamation, the Federal Highway Administration, the U.S. Nuclear Regulatory Commission, American Society of Civil Engineers and the ASCE's Geo-Institute, the Los Angeles Department of Water and Power, the Port of Long Beach, and the Port of Los Angeles. The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit http://national-academies.org.  A roster follows.

 

Contacts:

Riya V. Anandwala, Media Relations Officer Rebecca Ray, Media Relations Assistant Office of News and Public Information 202-334-2138; e-mail news@nas.edu national-academies.org/newsroom

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Copies of State of the Art and Practice in the Assessment of Earthquake-Induced Soil Liquefaction and Consequences are available at www.nap.edu or by calling 202-334-3313 or 1-800-624-6242. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).

 

THE NATIONAL ACADEMIES OF SCIENCES, ENGINEERING, AND MEDICINE

Division on Earth and Life Studies

Board on Earth Science and Resources

 

Committee on the State of the Art and Practice in Earthquake Induced Soil Liquefaction Assessment

 

Edward Kavazanjian Jr.1 (chair)

Regents Professor and Ira A. Fulton Professor of Geotechnical Engineering

School of Sustainable Engineering and the Built Environment

Arizona State University

Tempe

 

Jose E. Andrade

Professor of Civil and Mechanical Engineering

California Institute of Technology

Pasadena

 

Kandiah Arulmoli

President and Principal Engineer

Earth Mechanics Inc.

Fountain Valley, Calif.

 

Brian F. Atwater2

Geologist

U.S. Geological Survey, and

Affiliate Professor

Department of Earth and Space Sciences

University of Washington

Seattle

 

John T. Christian1

Consulting Engineer, and

Professor

Department of Environmental and Civil Engineering

University of Massachusetts, Lowell

Burlington

 

Russell Green

Professor of Civil and Environmental Engineering

Department of Civil and Environmental Engineering

Virginia Polytechnic Institute and State University

Blacksburg

 

Steven L. Kramer

Professor

Civil and Environmental Engineering

University of Washington

Seattle

 

Lelio Mejia

Principal Engineer and Vice President

AECOM

Oakland, CA

 

James Mitchell1,2

University Distinguished Professor Emeritus

Virginia Polytechnic Institute and State University

Blacksburg

 

Ellen Rathje

Associate Professor

Department of Civil, Architectural, and Environmental Engineering

University of Texas

Austin

 

James R. Rice1,2

Mallinckrodt Professor of Engineering Sciences and Geophysics

Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences

Harvard University

Cambridge, Mass.

 

Yumei Wang

Geohazards Engineer

Oregon Department of Geology and Mineral Industry

Portland

 

STAFF

 

Sammantha L. Magsino

Study Director

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1Member, National Academy of Engineering

2Member, National Academy of Sciences