SUMMARY
Considerable bridge‐ground interaction effects are involved in evaluating the consequences of liquefaction‐induced deformations. Due to seismic excitation, liquefied soil layers may result in substantial accumulated permanent deformation of sloping ground near the abutments. Ultimately, global response is dictated by the bridge‐ground interaction as an integral system. However, a holistic assessment of such response generally requires a highly demanding full three‐dimensional (3D) model of the bridge and surrounding ground. As such, in order to capture a number of the salient involved mechanisms, this study focuses on the longitudinal seismic performance of a simpler idealized configuration, motivated by details of an existing bridge‐ground configuration. In this model, a realistic multilayer soil profile is considered with interbedded liquefiable/nonliquefiable strata. The effect of the resulting liquefaction‐induced ground deformation is explored. Attention is given to overall deformation of the bridge structure due to lateral spreading in the vicinity of the abutments. The derived insights indicate a need for such global analysis techniques, when addressing the potential hazard of liquefaction and its consequences.
Dynamic ground and ground-structure responses are heavily dependent on the soil shear wave velocity. During seismic excitation, soil stiffness inferred from the shear wave velocity (Vs) might change significantly and affect the overall system response. In this study, an instrumentation and analysis framework was developed to allow for continuous estimation of Vs during dynamic/seismic excitation. The framework is presented along with representative applications during shake table testing of saturated sand strata. For that purpose, results from two different 1-g shake table tests conducted in a laminar soil container are examined and analyzed. In this context, evolution of the soil Vs profile during the shaking event is tracked and documented. The experimental setup, test procedure, and test results are described. Time histories of Vs at different depths within the sand strata are discussed. Overall, the developed techniques can be conveniently included in routine 1-g and centrifuge shake table experimentation efforts, when properly accounting for the differences between sizes of 1 g and centrifuge models.
Due to seismic response, accumulation of permanent ground deformation (lateral spreading) is an important mechanism of much practical significance. Such deformations typically occur near a ground slope, behind retaining structures such as sheet-pile and quay walls, and in mildly-sloping ground. In conducting a shake table test, the generation of permanent deformations further elucidates the underlying mechanisms and allows for related ground-foundation-structure response insights. In this paper, an approach for development of accumulated ground deformations is presented, in which asymmetric inertial loading results in a biased dynamic one-dimensional shear state of stress. As such, the proposed approach allows for further insights into the soil cyclic response and pore pressure build-up, with deformations accumulating in a preferred direction. In order to permit a virtually unlimited number of such loading cycles, focus is placed on motions that do not cause the shake-table actuator to accumulate displacement, in view of its possible limited stroke. Using this approach, representative experimental response is outlined and discussed. This experimental response can be used for calibration of numerical models to emulate the observed permanent strain accumulation profile and associated mechanisms. In addition to liquefaction-induced lateral spreading, this asymmetric shaking approach might be beneficial for a wide class of earthquake engineering shake table testing applications.
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