Response of pile foundations to simulated earthquake loading: Experimental and analytical result

To provide a reliable data base suitable for checking various models of dynamic pile foundation response to earthquake shaking, a series of small scale model tests on single piles and pile groups embedded in dry sand foundations were carried out on shaking tables. A similar series of tests were carried out using a geotechnical centrifuge equipped with a base motion actuator. Both the shake table and centrifuge single pile tests were carried out using both sinusoidal and random earthquake input motions over a range of shaking intensities. From the data, details of soil-pile interaction were elucidated. This provided a basis for improvement in methods of estimating required input parameters used in the dynamic analysis of pile foundations.;Prior to each test, shear wave velocity measurements were made throughout the prepared sand foundations using piezoceramic bender elements. The shear wave velocity data were used to compute small strain, elastic shear moduli in the soil. Elastic compression wave velocities were also identified from the bender element responses recorded during the shake table tests.;The single pile tests demonstrated that significant non-linearity and strain softening occurs in near field soil response, which is responsible for reductions in fundamental vibration frequency and pile head stiffness parameters with increasing amplitudes of lateral pile vibration. An analysis technique developed to estimate average effective strains around a single pile leads to predictions of large modulus reduction around the pile, depending on the amplitude of pile vibration.;Soil reaction pressures (p) due to relative horizontal movement between the soil and the pile (y) were deduced from the test data for various cycles of shaking, or so-called p-y curves. The cyclic p-y curves developed show clearly the non-linear, hysteretic near field response near the pile head. Approximately linear elastic p-y response occurs at greater depth. Material damping inferred from the area within the p-y hysteresis loops increases, in general, with increasing pile deflection level.;Comparing the flexural response observed on single piles during the shake table and centrifuge tests, the depth of maximum bending moment relative to the pile diameter has been observed to be greater in the shake table tests. Damping in the low stress level environment of the shake table has been found to be greater than under full scale stress conditions in the centrifuge.;Two-pile tests, where the piles have been oriented inline, offline or at 45 degrees to the direction of shaking, indicate that pile to pile interaction is very strong for inline and 45 degree shaking, and is relatively minor for offline shaking. For close pile separations during inline shaking, elastic theory underpredicts the extent of interaction.;Predictions of single pile response to earthquake shaking have been made using an uncoupled, sub-structure approach incorporating non linear pile head springs and equivalent viscous dashpots (foundation compliances) derived from the test data. (Abstract shortened by UMI.).