Dynamic Response and Impedance Functions of Foundation Resting on Sandy Soil Using Physical Model Tests

Abstract eng:
Experimental results to investigate the dynamic behavior and impedance function of foundations resting on a sand layer are presented in this paper. Physical model block vibration tests were carried out in a cubic steel container of size 1.0 m×1.0 m×0.8 m using foundations in three shapes, circular, square, and rectangular. The radius of the circular one was 7.5 cm and the two other types had the same radius of the equivalent circle, where the aspect ratio of the rectangular foundation was L/B = 2. The employed vertical force generator was a vibration exciter system, driven by a power amplifier. Using available sea sand, a sandy sample with specific density was prepared, and tests were carried out for three different footing shapes, by varying contact pressure and causing embedment for footing. The impedance functions for the different above conditions were calculated and compared with the preceding numerical and experimental works. It was observed that the stiffness and damping of the supporting soil are both functions of the vibration frequency, which are mainly because of boundary conditions especially side walls. Also two resonance frequencies were observed in the test results, where one is because of the wave’s reflection (waves emanating from the oscillating foundation reflect at the soil-container interface and return back to their source at the surface) and the other is because of the system’s inertia and the system’s natural frequency.

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