Jin-Tae Han

Dynamic P-Y Curves for Dry Sand from Centrifuge Tests

In this article, the simplified dynamic p-y backbone curve was suggested through a series of dynamic centrifuge tests. The centrifuge tests were carried out for a single pile in dry sand, while changing the conditions such as pile diameters, relative densities, input acceleration amplitudes and frequencies. Based on the results, the dynamic p-y backbone curve was formed as a hyperbolic function by connecting the peak points of the resulting experimental dynamic p-y curves, which corresponded to the maximum soil resistances. In order to represent the p-y backbone curve numerically, the initial stiffness and the ultimate subgrade reaction of soil, which are required to formulate the p-y backbone curve, were proposed as a function of the properties of a pile and soil. The dynamic p-y backbone curve was compared with the p-y curves that are currently used in practice. Also, the applicability of the dynamic p-y backbone curve was verified using psuedo-static analysis, and the analysis result using the backbone curve more successfully simulated the other centrifuge test results than that using the existing p-y curve.

3D Numerical Simulation of a Soil-Pile System Under Dynamic Loading

In this research, a new modeling method for simulation of the dynamic behavior of a pile, which can be applied to the conventional finite difference analysis program FLAC 3D, was developed to reduce the calculation time. The soil domain in this method is divided into a near-field region and a far-field region, the latter of which is not influenced by the soil-pile dynamic interaction. The ground motion of the far-field is then applied to the boundaries of the near-field instead of modeling the far-field region with finite meshes. In addition, the non-linear soil behavior is modeled by using the hysteretic damping model, which determines the soil tangent modulus as a function of shear strain and the interface element was applied to simulate the separation and slip between the soil and pile. The proposed method reduced the calculation time by as much as two thirds compared to the usual modeling method, while maintaining the accuracy of the calculated results. The calculated results by the proposed method showed good agreement with the prototype pile behavior, which was obtained by applying a similitude law to the 1-g shaking table test results.

Development of predicting method for dynamic pile behavior by using centrifuge tests considering the kinematic load effect

A series of dynamic centrifuge tests was conducted, with different pile diameters installed in dry and loose saturated sand deposit (liquefiable sand), for various conditions of input acceleration and upper mass. The test results revealed that the inertial force generated by the superstructure and the kinematic force generated by the soil movement were out-of-phase, and acted in opposite directions regardless of the ground condition. Based on the experimental results, an evaluation method for quantitatively calculating the kinematic force acting on a pile foundation was suggested using the inertial force of a trapezoidal soil wedge component. The method for predicting dynamic pile behavior considering kinematic effects was suggested by using the kinematic force evaluating method. The proposed method predicted the dynamic pile behavior better than the existing method.

Evaluation of 1-G Similitude Law in Predicting Behavior of a Pile-Soil Model

A series of 1-g shaking table tests was performed using a pile-soil model to verify the existing similitude law used in 1-g shaking table tests. Modeling of the model technique was used for three different sizes of the model, manufactured according to Iais similitude law, and tests were carried out while varying input parameters, such as input frequency and input ground acceleration. Evaluation of the accuracy of Iais scaling factor of a frequency showed that the maximum error in the converted frequency could be within 17%, 35% and 55% when the scaling factor is 2, 5 and 20, respectively. Combining the error occurring in the estimation of frequency, with the possible error occurring in the test results, the maximum error was found to be less than 9%, 21% and 59% when the scaling factor was 2, 5, and 20, respectively, when the frequency ratios in the model tests were smaller than 0.6. Therefore, it can be concluded that the 1-g shaking model test, based on Iais similitude law, can be used on a quantitative basis to predict the dynamic behavior of a pile foundation.