Drilled Shafts Subjected to Combined Effects of Lateral Spreading and Superstructure Inertia-Paper

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The study examines how superstructure inertia and liquefaction-induced lateral spreading interact to load pile foundations. Researchers analyzed a full-scale shake-table test of a 0.25 m diameter reinforced-concrete pile in gently sloping ground, with a nonliquefiable dry-sand crust over saturated sand layers. Instrumentation measured pile strains and movement, soil displacement, pore pressure, acceleration, and soil pressure against the pile.<br /><br />The test showed that the interaction changed during shaking. After liquefaction began, inertial movement of the pile upslope coincided with downslope pressure from the surface crust, so the two loads acted in opposing directions. During downslope inertial cycles, however, crust pressure was absent. Soil displacement had created a gap on the pile’s downslope side, and the pile head moved ahead of the surrounding soil. Shallow pile strains were associated with the opposing inertial and crust loads; deeper strains were associated with downslope inertia without a concurrent crust load.<br /><br />These observations suggest that inertial and lateral-spreading loads may not always peak together or combine straightforwardly. The findings offer one possible loading scenario for design, but derive from a single test and depend on the soil, pile, and shaking conditions. Because load interaction is site- and project-specific, designers should consider this behavior alongside scenarios in which inertial and spreading loads are combined.

Keywords

superstructure inertia

liquefaction

lateral spreading

pile foundations

full-scale shake-table test

reinforced-concrete pile

soil-pile interaction

pile strains

pore pressure

ground shaking