Centrifuge Modeling of Permeabilty and Pinning Reinforcement Effects on Pile Response to Lateral Spreading

L.L. Gonzalez-Lagos, T. Abdoun and R. Dobry

MCEER-07-0020 | 12/10/2007 | 382 pages

Keywords: Centrifuge modeling.  Seismic vulnerability assessments.  Highway infrastructure.  Bridges.  Ground failure.  Liquefaction.  Lateral spreading.  Pile group foundations.  Soil permeability.  Reinforcing effects.  Pinning effects.

Abstract: The vulnerability of highway bridges to earthquake-induced ground failures arising from liquefaction has been clearly demonstrated by the extensive damage observed in the past earthquakes, particularly when a nonliquefied soil layer rides on top of the liquefied soil. Liquefaction induced lateral spreading may be reduced by the restraining forces provided by pile group foundations. This reduction in lateral displacement reduces the loads and displacement demands that are imposed on the piles. The first part of this work presents experimental results and analyses of six centrifuge tests that were conducted at the 150 g-ton RPI centrifuge to investigate the effect of soil permeability in the response of single piles and pile groups to lateral spreading. In the models that simulate a liquefiable coarse sand layer (saturated with water), the piles bounced back after a couple of cycles of shaking; however in the models that simulate a liquefiable fine sand layer (saturated with viscous fluid), the piles never bounced back, reaching maximum displacements and bending moments as large as 6 times the one measured in the models saturated with water. In the models with lower soil permeability (saturated with viscous fluid) the results and analyses indicate that negative excess pore pressures developed close to the foundations stiffened the soil, increasing the effective area subjected to the liquefied soil pressure, explaining hence the large bending moments. The second part presents experimental results and analyses of four centrifuge tests that were conducted at the RPI centrifuge. The project was to study the reinforcing or pinning effect the pile groups have on the lateral spreading. An analysis approach developed in this study proved to be very useful in understanding the reinforcement effect pile groups have in liquefaction induced lateral spreading and to give a good estimation, at least in centrifuge modeling, of the expected pile group deformations.