The behavior of pile foundations under earthquake loading is an important factor affecting the performance of such structures. Observations from past earthquakes have shown that piles in stiff soils generally perform well, while those installed in soft or liquefiable soils are more subjected to problems arising from ground amplification or excessive soil movements.
A series of laboratory tests were conducted to measure the response of pile foundation when subjected to dynamic loads. A special vibration box was manufactured. The accompanied measurements include vertical and horizontal displacement and settlement of pile cap, acceleration in three dimensions in both soil and cap and earth pressures. The model pile used has an outer diameter of 18 mm and inner diameter of 15 mm. A group of (2x2) piles was tested.
It was concluded that for soil bed in dry state, the acceleration amplitudes increase with frequency for both soil relative densities (loose and medium). The maximum acceleration in the foundation is lower than in soil bed for all operating shaking frequencies and soil states. The decreasing of the maximum acceleration recorded in the foundation as compared to that in the soil bed is between 10-100 % for loose and medium state of soil, and the decrease in loose state is more than in medium state. This means that there is damping effect or attenuation of vibration waves
