Dynamic and Cyclic Properties of Soils

Response of soil depends on both the mechanical properties of soil itself and the nature of loading. Many geotechnical engineering problems are associated with dynamic and cyclic loadings, such as ocean wave or ice loading applied on foundations of offshore structures or bridges, dynamic loading applied on foundations of offshore wind power structures, ocean wave loading on harbor structures, seismic wave propagation through soils, machine vibration-induced loading on foundations, seismic loading, liquefaction and cyclic transient loading, and dynamic working loads [113]. Soils’ responses subject to dynamic and cyclic loadings are strongly controlled by the mechanical properties of the soil, which basically include shear modulus (shear wave velocity), damping, Poisson’s ratio, and density (mass). Of these, shear modulus and damping are the most important material properties with which to characterize the dynamic behavior of soils. Both these properties are affected by effective stress and over-consolidation ratio. While the determination of shear modulus is normally well established, the damping modeling is less clearly understood. Furthermore, both shear modulus and damping depend on the strain level, while the strain response level also depends on the modulus and damping. Moreover, at high strain levels, in addition to the strain level, other parameters such as rate and number of cycles of cyclic loading are also important influences on the shear modulus. The strain rate of soils due to dynamic loading also influences soils’ strength (mainly for clay soils) and shear modulus, as will be presented in Sect. 2.5. Volume change characteristics are also important at high strain levels. In addition, the location of the water table, degree of saturation, and grain size distribution may be important, especially when liquefaction is a potential problem. All the issues above complicate the geotechnical analysis and challenge analysis accuracy requirements.