Dynamic Lateral Response of a Pile Group in Clay

Abstract

A series of lateral dynamic loading tests were conducted on a rigid concrete cap supported by nine 273-mm-diameter steel pipe piles in a square group. The piles were driven 13.7 m into a layered deposit of overconsolidated clay. A linear inertial mass vibrator applied horizontal constant-rate frequency sweep and steady state loadings from frequencies above the first mode resonance to frequencies below the resonance frequency of the pile-soil-cap system at several amplitudes of dynamic load. Sixty channels of system response data were recorded for each test. Frequency response functions between the applied load and points on the pile cap, points on the embedded piles, and locations in the surrounding soil were computed by standard digital signal processing techniques. The average measured pile cap frequency response function peak amplitude was 1.03 × 10−4 mm/N, or about 10 times the static flexibility, and the horizontal resonance frequency was about 7.5 Hz. The measured performance of the group was interpreted in terms of simple modeling techniques.