Nonlinear Dynamic Behaviour of Pile Foundations in Horizontal Vibration

Horizontal vibration tests are performed on reinforced concrete single pile (L/d = 20) and group piles (L/d = 20 and s/d = 2, 3, 4) under varying levels of harmonic excitation acting above the center of gravity of the pile cap-loading system. The observed response curves display marked nonlinearity as the natural frequencies decreases with increasing intensity of excitation for both horizontal and rocking mode of vibrations. The measured response is compared with linear elastic and nonlinear solutions of Novak's continuum approach. To account for the nonlinear response of the piles, provisions are made for yielding of soil around the piles by introducing the weak boundary zone concept. Different separation length between the pile and top soil is also considered for different excitation intensities in the nonlinear analysis. It is found that a close agreement can be achieved between theoretical predictions and measured response curves by allowing for boundary zone and separation between pile and soil. It is also found that the boundary zone parameters, pile-soil separation, pile-soil-pile interaction and the embedded effect of the pile cap play a major role in the coupled dynamic response of pile foundation.