5TH International Congress on Technology - Engineering & Science - Kuala Lumpur - Malaysia (2018-02-01)

Analysis Of Soil-pile Systems Subjected To Dynamic Loads

In this study, the behavior of soil-pile systems subjected to dynamic loads in dry sand was investigated using 1g shaking table tests. The size of the soil box was 1,200 600 800 mm with sponge pads 50 mm thick on the sidewalls to reduce reflection waves during shaking. The model pile was made of aluminum alloy with a hollow circular section. Jumoonjin sand, characterized as clean and uniform sand, was used in the tests. Sweep tests were conducted to evaluate the natural frequencies of the soil-pile systems under various conditions. As the acceleration amplitude increases, the natural frequency of the soil-pile systems decreases due to the reduced elastic modulus of the soil. Additionally, As the surcharge mass increases, the natural frequency of the soil-pile systems decreases due to the greater inertia forces induced. In addition, the natural frequency of the soil-pile system for the relative density of 40%, is smaller than that for the relative density of 80% due to the increased stiffness in the soil with a higher relative density. A series of model tests were performed to analyse soil-pile systems under dynamic loads. The input wave was as a sine wave and applied approximately 5 seconds. The loading frequencies used in the tests were calculated from the natural frequencies (fn) of the soil-pile systems. The natural frequencies range from 0.4fn Hz to 1.6fn Hz. The amplitude accelerations ranged from 0.098 g to 0.4 g. The dynamic p-y curves are flat near the surface and become stiffer with depth because the soil confining stress increases. the lateral pile deflection increases with the acceleration amplitude due to greater inertial forces. The soil resistance also increases with the acceleration amplitude. However, the increments of the soil resistance decreased with the acceleration amplitude. The secant slope of the dynamic p-y curve decreases with an increase in the acceleration amplitude. The dynamic p-y curve is closely related to the ratio of the loading frequency to the natural frequency. As the frequency ratio approaches 1.0, the lateral deflection further increases, and the slope of the dynamic p-y curve decreases due to resonance. Additionally, as the surcharge mass increases, the slope of the dynamic p-y curves decreases due to the greater inertia forces induced. Based on the results of this study, the natural frequency of the soil - pile system is largely affected by the stiffness and surcharge mass. Additionally, the dynamic p-y curve is largely affected by the relation between the natural frequency of the soil-pile system and the loading frequency, the confining stress of the soil and inertia forces such as the acceleration amplitude and surcharge mass.
Hyunsung Lim, Sangseom Jeong