Comparison of Static and Dynamic Lateral Stiffnesses of a Driven Pile

Accurate modeling of support conditions is important in the analysis of bridges for seismic loading. To address the problem of modeling the soil-structure interface of bridges supported by piles driven in loess in West Tennessee, a series of quick-release ("pluck") tests were performed. In the process of performing the pluck tests, sufficient static lateral load was applied to a large mass supported by a single pile to achieve a prechosen lateral displacement. This load was released; dynamic response was monitored; dynamic stiffness coefficients were calculated. A static stiffness was also calculated as simply the applied load divided by the prechosen deflection. The "secant" stiffness values thus obtained were compared to the dynamic stiffness values, and the two stiffness values were found in all cases to be essentially equal. This fact suggests the use of static lateral load tests to determine appropriate values of stiffness to use in modeling the pier-pile interface for purposes of dynamic analysis of a bridge.