AnEvaluation of LPILE in Comparison to the Measured Behavior of Prestressed Concrete Piles in Integral Abutments

The Tennessee Department of Transportation (TDOT) has designed and built integral abutment bridges with prestressed concrete piles for many years. A product of constructing integral bridge abutments is that the piles supporting the structure are exposed to lateral deflections, which come mainly from thermal expansion and contraction of the bridge structure. TDOT funded a project in which the University of Tennessee, Knoxville investigated the effects of the lateral displacement of four 14 inch square prestressed concrete piles that were driven into virgin clay soil.

The tests involved full scale lateral loading each of the four prestressed piles; each pile supported a simulated integral bridge abutment. After each pile was driven into the ground, the model abutment and a "pulling slab" were cast on top of the pile. Leaving one foot of pile exposed between the abutment and the ground, University personnel instrumented each pile with strain gages on that exposed surface. The tests then included a basic testing regime of lateral displacements that depended on incremental displacement and time rate of loading. During the tests, moments, deflections, and shears were recorded at the pile-abutment interface.

LPILE is a program that uses a finite difference analysis to calculate the behavior of a pile. While the piles in the field were not instrumented below the surface of the ground, LPILE was used to develop moment versus depth diagrams. Also the analysis evaluated shear and displacement versus depth graphs. LPILE was evaluated on its ability to predict the values measured at the pile abutment interface in the field tests and the consistency with which LPILE located maximum values and inflection points. The LPILE analyses were crude approximations of measured values.