Ross W. Boulanger

Prof Ross W. Boulanger PhD, PE, NAE

Professor and Director, Center for Geotechnical Modeling. University of California at Davis, U.S.A.

Biography

Professor Ross W. Boulanger is the Director of the Center for Geotechnical Modeling in the Department of Civil and Environmental Engineering at the University of California, Davis. He received his PhD and MS degrees in Civil Engineering from the University of California at Berkeley, and his BASc degree in Civil Engineering from the University of British Columbia. His research and professional practice are primarily related to liquefaction and its remediation, seismic performance of dams and levees, and seismic soil-pile-structure interaction.

Over the past 25 years, he has produced over 250 publications and served as a technical specialist on over 50 seismic remediation and dam safety projects. His honors include the TK Hsieh Award from the Institution of Civil Engineers, the Ralph B. Peck Award, Norman Medal, Walter L. Huber Civil Engineering Research Prize, and Arthur Casagrande Professional Development Award from the American Society of Civil Engineers (ASCE), and election to the US National Academy of Engineering.

Abstract

Modeling slope instability due to undrained creep in clays and plastic silts

Ross W. Boulanger, PhD, PE, Professor, University of California at Davis, Davis, California, USA

Tyler J. Oathes, Graduate Student Researcher, University of California at Davis, Davis, California, USA

Undrained creep rupture in saturated silts and clays that are initially loose of critical state can lead to delayed slope instability after relatively minor changes in loading, and has been suspected as contributing to a number of static failures in tailings dams and other geotechnical structures. This paper illustrates the numerical modeling of undrained creep rupture for a hypothetical tailings dam using the two-dimensional finite difference program FLAC with a new user-defined strain-rate dependent constitutive model PM4SiltR. The constitutive model is introduced briefly, followed by single element simulations to illustrate its stress-strain responses under a range of loading conditions and strain rates. Simulations are then presented for the tailings dam with different initial seepage conditions and modest wetting-induced increases in loading. The analysis results illustrate the process of undrained creep rupture leading to slope instability, including the potential for small changes in loading to cause delayed instability. The numerical modeling approach and constitutive model are shown to provide reasonable approximations of undrained creep behaviors that can be important for static slope stability evaluations. Challenges in quantifying creep and progressive failure effects for static slope stability evaluations in practice are discussed.