Field Testing and Analyses of a Batter Pile Group Foundation under Lateral Loading

Abstract

Much of the new I-10 Twin Span Bridge, built over Lake Pontchartrain between New Orleans and Slidell, Louisiana, is supported by driven batter pile group foundations. To assess the methodology used to design and analyze batter pile foundations and to evaluate their performance under lateral loading, a full-scale lateral load test was conducted on an M19 eastbound pier of the new bridge. The M19 pier foundation consisted of 24 precast, prestressed concrete 110-ft-long batter piles; eight piles were instrumented with in-place inclinometers (IPIs), and 12 piles were instrumented with strain gauges. The test was conducted by pulling the M19 eastbound and westbound piers toward each other with high-strength steel tendons. A maximum 1,870-kip lateral load was applied in increments. A high-order polynomial curve-fitting method was applied for each load increment to fit the measured rotation profiles from the IPIs, and the fitted rotation curves were used to deduce the bending moment, shear force, and soil reaction profiles on the basis of specific mathematical derivations. The calculated moments from curve fitting were compared with the moments calculated from strain gauge measurements, and the results showed good agreement. The soils’ p-y curves at different depths were backcalculated from the derived soil reaction profiles. The resulting p-y curves showed no evidence of group effect. The FB-MultiPier program was also used to analyze the behavior of the M19 pier foundation under lateral loading. Comparison of FB-MultiPier results with measured values as well as values calculated from polynomial curve fitting showed that FB-MultiPier overpredicted the lateral deformations of batter pile group foundations.