Pile Pinning and Interaction of Adjacent Foundations During Lateral Spreading-Article

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The study examines how the size of a liquefaction-induced lateral spread and nearby bridge foundations affect the loads on piles. It distinguishes <strong>pinning</strong>—reduced foundation demand when the spread is too limited to encompass the foundation’s full zone of influence—from <strong>shielding</strong>, where one foundation reduces the demand on an adjacent foundation.

The authors analyze two parallel bridges over the Colorado River in Mexico that were affected by the 2010 El Mayor–Cucapah earthquake. The railroad bridge suffered major movement and a span collapse, while the nearby highway bridge experienced only moderate damage. Free-field ground displacement was estimated at about 4.6 m.

To estimate foundation interaction, the authors combined equivalent-static analyses (ESA) with two-dimensional finite-element modeling of the moving surface crust. The model represented the highway bridge foundations and estimated how much they reduced ground displacement at the railroad bridge. It predicted a roughly 70% reduction in lateral-spreading demand at the railroad bridge’s Bent 5. ESA using this reduced demand predicted about 1.2 m of movement, broadly consistent with the approximately 1 m observed. Using the full free-field displacement substantially overpredicted movement. Shielding occurred both across the gap between bridges and along the bridges; the highway bridge also partly shielded its own bents.

The study further shows that spread length matters: short spreads can impose lower loads than broad spreads with the same free-field displacement. The proposed method is approximate and is best suited to cases where a single crust layer dominates soil–foundation load transfer. Its results depend on the assumed geometry and soil properties, so project-specific boundary conditions should be considered, and more sophisticated analysis may be warranted for critical structures.

Keywords

liquefaction

lateral spread

pile loads

bridge foundations

pinning

shielding

finite element modeling

equivalent-static analysis

Colorado River

El Mayor–Cucapah earthquake