A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering at the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M.Eng.) - Asian Institute of Technology, 1974

Model tests were performed under laboratory conditions in order to obtain a better understanding of the strain distribution in the soil under a circular footing undergoing steady-state vertical oscillations. Four sand beds having two different densities and moisture contents were used as elastic half-space models. The vertical and radial strain components were measured by means of soil strain sensors embedded within the sand along lines extending radially from the source of excitation and the axis of symmetry. In order to evaluate the dynamic properties of the soil, the vertical component of surface displacement along radial lines extending from the source was also measured using vertical velocity transducers. From the measured strain amplitude the stress distribution beneath the footing could be determined. The tests results showed that the variation of strain amplitude was consistent with the theory. Measured resonant frequencies agreed fairly well with predicted ones, and the maximum strain occured at a depth approximately equal to the radius of the footing. The tests also revealed that the presence of moisture decreased the strain amplitudes and increased the resonant frequency, due to enhancement of material damping. The results also showed that the vertical stress distribution beneath the footing exhibited a character intermediate between a "rigid base" type and a "parabolic" type distribution.