Measurement of frozen soil–pile dynamic properties: A system identification approach

A free-decay response signal approach is proposed for reliable estimation of frozen soil–pile dynamic properties of a partially embedded pile. Theoretical consideration and approximations are given for the free vibration of pile structures, with 20% of the pile cantilevered aboveground and the remaining embedded in Fairbanks silt. Winter measurements were taken for free-decay response of the pile. A comprehensive frequency spectrum analysis that includes fast Fourier transform, power spectrum density, and spectrograms is used to evaluate the systemʹs vibration properties. Empirical mode decomposition is then used to decompose the signal to extract specific components for parameter identification. Results show that the response exhibits time-variant and nonlinear characteristics in the time–frequency domain. Experimental data show that the tested system exhibits weak nonlinearity. Dominant system parameters, used to characterize frozen soil–pile interactions, are identified. Two dominant frequencies for a stiff pile embedded 20 ft (6.096 mm) deep in frozen Fairbanks silt are 97 Hz and 1080 Hz. Damping was found to be approximately 0.016.