Dynamic Loadings

Criteria for placing and improving soil sustaining dynamic loadings are presented for building and machinery foundations and for earth embankments. These criteria are compared and their limitations in practice without consideration of the response of the soil and structure to dynamic loadings are illustrated. Vibratory-induced settlement of footing supported on granular soils depends on the dynamic stresses and accelerations. For accelerations less than 1 g, for most practical cases, accelerations per se do not cause sand densification. Rather, accelerations produce inertia stresses whose continued repetition results in orientation of sand grains and settlement. Confining pressure, density, grain size, dynamic stress, its magnitude and repetition, etc., influence liquefaction of granular soils. These factors are considered in appropriate design criteria for foundations. Analytical procedures developed by Seed, Ambraseys and Sarma, and Newmark for stability and deformations of earth dams in seismic regions are presented.