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Modulus and damping equations of sands subjected to combined dynamic loadings

Abstract Dynamic loading due to earthquakes is made up of combinations of different wave types, including compressive waves, shear waves, etc. It has been shown that if a soil specimen is subjected to a combined longitudinal and torsional sinusoidal loading, significant degradation of the specimen occurs wherein the modulus is reduced and the damping increased more than for a single excitation. The use of dynamic properties obtained from such combined loadings are more representative of actual field conditions than those from single-loading conditions. Testing sands subjected to random and impulse types of combined loading demonstrates that octahedral shear strain is a useful parameter for describing the effects of combined loading as in the case of sinusoidal loading. The paper presents equations for the determination of the shear modulus, Young's modulus, and damping of sandy soils subjected to these combined loadings. From the equations, the degree of specimen degradation can be determined, as well as the threshold strain ratio needed for the degradation to occur.