STATNAMIC LATERAL LOAD TESTING OF A FULL-SCALE FIXED-HEAD PILE GROUP

The lateral load capacity of pile foundations is critically important in designing bridge structures to resist seismic forces. Although fairly reliable methods have been developed for predicting the lateral capacity of single piles under static loads, there is very little information to guide engineers in the design of closely spaced pile groups (i.e., spacings less than 6 pile diameters) under dynamic loads. In addition, the dynamic resistance provided by backfill behind the pile cap and interface friction at the base of the pile cap is poorly understood. Although numerical and centrifuge models can provide some guidance regarding these questions, a reasonable number of full-scale load tests are necessary to verify these models and provide ground truth information. To improve our understanding of pile group behavior under dynamic lateral loads, a series of lateral load tests was recently performed on a full-scale pile group at the Salt Lake International Airport. The dynamic loading was applied to the pile cap by means of a horizontally oriented Statnamic loading device. This device was capable of producing loads of several thousand kN with durations of 100 to 250 msec. Tests were performed with and without backfill behind the pile cap so that the resistance provided by the backfill could be evaluated.