Slope failures caused by earthquakes have had a significant impact on the design of slopes and earth retention systems in areas of strong seismicity. It commonly is assumed that the stability of clay deposits can be evaluated through the residual undrained strength that is applicable at large deformations. This conservative assumption does not explicitly account for the magnitude and duration of the seismic shaking and neglects the role of the inherent natural structure of clay, thus preventing a mechanistic description of initiation of failure in clays. This effort proposes a new approach for quantifying the strength degradation and destructuration of natural clays exposed to cyclic loading. It will combine experimental and theoretical findings to predict the onset of seismically-induced failure in natural clay deposits. Experiments will be conducted on high quality samples of Bootlegger Cove Formation (BCF) of varying degrees of sensitivity. Very sensitive clays in this formation triggered the catastrophic slides that took place in Anchorage during the 1964 earthquake. Northwestern will collaborate with GeoEngineers, Inc. in this effort. The experimental program will include monotonic and cyclic tests on intact and reconstituted samples. Results will elucidate the role of material nonlinearity, stress-paths, consolidation history and cyclic loading. The modeling activities will use this evidence to formulate a plasticity-based non-linear constitutive model reproducing the effect of destructuration in pore pressure build-up and cyclically generated failure. The approach will include the development of specific bifurcation criteria for assessing the cyclic strength degradation as a function of stress conditions and number of cycles. The model will be numerically implemented in computer programs for coupled dynamic analysis of geotechnical problems.
|Effective start/end date||9/1/14 → 8/31/18|
- National Science Foundation (CMMI-1434876 001)
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