Numerical Modeling of Soil-Pile Interaction in Liquefying Soils for a Water Crossing Bridge

A recent design of a water crossing bridge encountered potential liquefiable soils beyond the depth that our standard-of-practice simplified liquefaction evaluation method (NCEER, 1997, Youd et al., 2001) can apply. A field investigation including deep soil borings and cone penetration test soundings was performed and revealed that loose to medium dense sandy alluvial soils are about 80 feet thick below the mud line. To evaluate liquefaction susceptibility of deeply buried soils and liquefaction effect on the response of the abutment Cast-In-Steel-Shell (CISS) piles, nonlinear effective-stress numerical models were built that were fullycoupled with a pore pressure generation scheme. The excess pore pressure ratios were calculated at various soil layers in the alluvium and the p-y curves were adjusted based on the reduced effective friction angles for partial excess pore pressure generation and based on the post-liquefaction residual strength for fully liquefied layers. A soil-pile-interaction model using the adjusted p-y curves connecting the CISS piles to soil grids was built and analyzed for pile bending moment, shear forces and deflections. The above values were further compared with those from the standard pseudo-static lateral pile capacity analyses. Differences are discussed and the recommendations for the bridge pile foundation design are made