Behavior of Dry Sands Under Cyclic Loading

The stress-strain characteristics of dry sands under cyclic loading is described. Within the range of stress and acceleration studied, the soil deformation state primarily of shear deformation. While the volumetric compression of the soil always increases under cyclic loading, its contribution to the total strain remains small. The magnitude of the principal stress ratio, above which large strains may develop under vibration, is dependent on the confining pressure. At a low confining pressure (7 psi) this ratio is about 1/2 of the principal stress ratio for failure in static tests. At a higher confining pressure (20 psi), it is about 3/4 of the static ratio for foundation vibration problems, the strong influence of the confining pressure implies that a rather important size effect may arise. For two foundations of unequal size, loaded to equal unit pressure, the zone of stressed soil beneath the larger foundation would extend to a larger depth. The average confining pressure on the soil in this zone would also be greater.