Collaborative Research: Dynamic Behavior of Slickensided Surfaces

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"Slickensides" are surfaces of weakness formed in stiff clays as a result of large shear displacements - on the order of 50 mm to 250 mm - concentrated on a discrete surface of sliding. Platy clay particles become aligned parallel to the surface of sliding, resulting in the formation of a smooth surface with shear strength that is much lower than the strength of the adjacent clay through which the slickensided surface forms.As a result of this low shear strength in comparison with the adjacent clay, slickensided rupture surfaces are likely loci of displacements during earthquakes. However, there have been no studies of the behavior of slickensided surfaces when subjected to the rapid cyclic loading that occurs during earthquakes. As a result, engineers must rely on assumption and judgment when estimating strengths for seismic deformation analyses, and these vary considerably among practicing engineers. For example, for one particular project in northern California, the difference of opinion regarding the shear strength that should be used resulted in recommendations for stabilization of the slopes that differed in cost by a factor of ten. At present, there is no way to determine whether one of these designs was dangerously inadequate, or the other was wasteful overkill.The broader impacts of this research program include opportunities for undergraduate and graduate students to participate in the laboratory experiments at Virginia Tech, and for freshman through senior-level students to observe the centrifuge experiments at UC Davis, and to work as assistants in preparing the centrifuge models. Both UC Davis and Virginia Tech have very active programs to recruit minority students to participate in research through the Minority Opportunities for Research in Engineering at UC Davis, and the Office of Minority Engineering Programs and coalition with Historically Black Colleges and Universities at Virginia Tech. The project also involves an active collaboration with Dr. Binod Tiwari of Niigata University, who has considerable experience in the types of experiments involved and will spend time at Virginia Tech and UC Davis, which will help to establish closer relationships between researchers in Japan and in the United States.