This paper presents an experimental study on natural frequency of a foundation on a layered soil system subjected to dynamic loading. Using a Lazan type mechanical oscillator, model block vibration tests on a footing made up of steel and of size 300×300×50mm are conducted. Three different static weights and three different eccentricities are used to simulate different vibrating mass and dynamic force level respectively. Two different types of layered systems (soft layer over stiff layer and stiff layer over soft layer) are considered and in each type thickness of top layer is varied. In total 90 tests are conducted and the effect of position and thickness of layering is investigated. It is observed that the natural frequency of the system decreases due to presence of the soft layer at the top whereas it increases due to presence of stiff layer at the top. It is also observed that presence of a soft layer at top is more dangerous than at depth. Further, it is found that the variation of natural frequency due to layering can be quantified by an equivalent lumped model. Performance of the method is found to be encouraging
The design of machine foundation involves a systematic application of the principles of soil engineering, soil dynamics and theory of vibration. Since the classical work by Lamb (1904) and subsequently by Reissner (1936), Bycroft (1956), Lysmer and Richart (1966) and Richart et al (1970), the subject of vibratory response of foundations has attracted the attention of several researchers. The state of the art on the subject has since then made significant strides. Methods are now available not only for computing the response of machine foundations resting on the surface of the elastic half space but also for embedded foundations and foundations on piles.