Interpretation of Lateral Load Test of Batter Pile Group Using High Order Polynomials Curve Fitting

A full-scale lateral load test was conducted on a batter-pile group foundation that supports the M19 eastbound pier of I-10 Twin Span Bridge over Lake Pontchartrain, Louisiana, to assess the validity of current methodology used to design pile foundations. The test was conducted by pulling the M19 eastbound and westbound piers toward each other using high strength steel tendons. A maximum of 1870 kips (8318 kN) static lateral load was applied in increments. The tested pile group consists of 24 driven square precast prestressed concrete (PPC), 110 ft. (33.5 m) long and 3 ft. (0.91 m) wide batter piles; among which 8 piles were instrumented with In-Place Inclinometers (IPIs) and 12 piles were instrumented with strain gauges. The batter piles were spaced 4.3 pile width in the direction of lateral loading. A seventh-order polynomial curve fitting method was applied, for each load increment, to fit the measured rotation profiles from the IPI inclinometers. The fitted rotation curves were then used to deduce the bending moment, shear force, and soil reaction profiles based on specific mathematical derivations. The calculated moments from curve fitting were compared with the moments calculated from strain gauges, and the results showed good agreements. The soils' p-y curves at different depths were also back-calculated from the derived soil reaction profiles. The resulted p-y curves showed no evidence of a group effect.