A micromechanical study of energy dissipation mechanisms in granular soils subjected to cyclic loading

Liquefaction of granular soils has been at the source of many structural failures during major earthquakes, and for this reason has been an extensively researched topic in the geotechnical engineering field. Numerous studies have used energy-based methods to define the liquefaction potential of a soil. Among these studies are those that apply the energy concept, which suggests that there is a specific amount of dissipated energy after which liquefaction will take place in a saturated granular soil. This study utilizes the discrete element method (DEM) to present a microscopic energy monitoring approach to characterize energy dissipation mechanisms in cyclically loaded soils.;Computational simulations of consolidated undrained (CU) cyclic triaxial tests are conducted using synthetic soil samples packed at various relative densities. The samples are subjected to strain-controlled cyclic sinusoidal and irregular random loading patterns of different frequencies and maximum shear strain amplitudes. The onset of liquefaction is illustrated through time histories of pore-water pressure and coordination number. The time histories of individual microscale energy components are then presented. A comparison is made between the dissipated energy calculated from microscopic energy components monitored in the simulations and macroscopic energy calculated based on the area of shear stress-shear strain loops. A number of simulations that resulted in liquefaction are discussed, and the energy concept for evaluating liquefaction potential is examined based on these results. The material damping ratio and specific damping capacity at both the microscale and macroscale are also presented.;Numerical simulations are also conducted on saturated deposits of granular particles subjected to seismic excitations, modeled using a transient fully-coupled continuum-fluid discrete-particle model. The macroscopic and microscopic response patterns are presented, followed by an in-depth look at the individual microscale energy components both before and after the onset of liquefaction. The impact of general seismic loading on liquefaction potential including the effects of excitation amplitude and frequency content, loading pattern (sinusoidal/random), and direction of the dynamic load (one-directional/twodirectional) is explored. The energy concept for evaluation of liquefaction potential is again examined based on the results of these simulations.;Results from the conducted simulations indicate that there may not be a specific amount of energy after which liquefaction will take place in a soil, especially for denser soil deposits. A sample with a specific packing density may dissipate different quantities of energy prior to liquefaction, depending on the amplitude of the applied shear strain and the nature of the dynamic load.