Degradation of Sands due to Combined Sinusoidal Loading

Dynamic loading due to earthquakes is made up of very complicated combinations of different types of waves including compressive waves, shear waves, etc. If a soil specimen is subjected to a combined longitudinal and torsional excitation, significant degradation of the specimen occurs, wherein the modulus is reduced and the damping increased more than for single excitation. This paper presents equations based on test results on clean sands for the determination of the shear modulus and damping of sandy soils for single and combined sinusoidal 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. The dynamic properties obtained from combined loadings will be more representative of actual field conditions than those from single-loading conditions.