Energy-based evaluation of liquefaction potential under non-uniform cyclic loading

Abstract

Uniform cyclic loading is commonly used in laboratory tests to evaluate soil resistance to earthquake-induced liquefaction, even if the cyclic stresses induced by earthquakes in the field are highly irregular. This paper discusses the use of stress and energy-based approaches to evaluate the liquefaction resistance of sand under irregular loading. Results of undrained cyclic triaxial tests including a large-amplitude singular peak loading cycle are presented and compared to those obtained using uniform loading. Although samples are subjected to loading patterns which would have been deemed equivalent by conventional stress-based methods, the number of cycles required to trigger liquefaction strongly depends on the amplitude and location of the peak within the loading history. Conversely, a unique relationship exists between the accumulation of dissipated energy per unit volume, computed using stress and strain measurements, and the observed residual pore water pressure build-up for all tests, throughout the entire cyclic loading application. This demonstrates that conventional laboratory tests using uniform loading conditions can be employed to determine liquefaction resistance if their interpretation is carried out based on energy principles.