COMBINED EFFECTS OF LATERAL SPREADING AND SUPERSTRUCTURE INERTIA

Abstract

The seismic behavior of a RC pile with a diameter of 0.25 m subjected to liquefaction-induced lateral spreading was investigated using a shake table experiment that was conducted at the University of California, San Diego by Professor Ahmed Elgamal and Dr. Ahmed Ebeido (Ebeido and Elgamal 2019). A sinusoidal motion was applied at the base of a model that was inclined by 4 degrees. The loose and dense sand layers liquefied during the test, resulting in a permanent lateral spreading displacement of approximately 0.4 m (Figure E1). The pile was subjected to the combined effects of inertial loads from the acceleration of the superstructure mass and kinematic loads from the overlying nonliquefiable, dry crust. The dynamic responses of the soil and pile were analyzed to evaluate the relative contributions of inertial and kinematic loads during critical cycles (i.e., at the time of maximum inertia and the time of maximum pile strains). It was found that large pile strains developed after liquefaction was triggered. Large pile strains (and curvature) were recorded at a shallow depth within the crust (0.49 m) and a deeper location below the loose liquefiable sand (1.89 m). Large pile strains at shallow depth were found to be correlated with the inertial loads applied in the upslope direction. These upslope inertial loads were resisted by downslope crust loads, indicating an out-of-phase interaction. In contrast, large pile strains that occurred at deeper locations were correlated with downslope inertial loads and were accompanied by zero crust load, indicating that there was no lateral spreading force during the downslope inertial cycles. A gap at the downslope area in front of the pile formed because the soil displacements exceeded the pile displacements during the cyclic phase after liquefaction was triggered. The lack of crust load during the downslope inertial cycles is attributed to the pile head outrunning the crust displacement and causing the pile to be pushed into the gap at the downslope area in front of the pile. The interaction of inertia and kinematics appears to be a site- and project-specific phenomena. Therefore,the findings of this study—and, specifically, the lack of lateral spreading crust load during downslope inertial cycles—should be considered in design as one possible scenario in addition to the scenarios from several other studies that suggest combining the inertial loads with a lateral spreading force (e.g., Boulanger et al. 2007, Turner et al. 2016, Souri et al. 2022, Tokimatsu et al. 2005, Cubrinovski et al 2017).