Dynamic Tests of Pipe Pile in Saturated Peat

Abstract

Dynamic quick‐release and forced‐harmonic vibration tests were performed on a steel pipe pile embedded in soft saturated peat. The translational and rotational pile‐head impedances (stiffness and damping values) estimated from the forced‐harmonic vibration tests were independent of frequency between 1.8 Hz and 3 Hz, the frequency range of the tests. These impedances were generally similar to those estimated from quick‐release tests at initial pile‐head offsets similar to the harmonic displacements generated during the forced‐vibration tests. However, the dynamic translational stiffness was less than the tangent stiffness obtained from earlier static load tests on the pile, a result attributed to cyclic degradation of the peat and possible experimental error. The calibration of simple theoretical models to the dynamic test data also indicated that large reductions in the apparent soil modulus occurred, and that this reduction was greatest near the ground surface where the pile deflections were largest. This observation and the low hysteretic damping indicated by the models suggest that a water‐filled gap may have formed between the pile and the peat during the dynamic tests.