Non-conventional lab and field methods for measuring frequency-dependent low-strain parameters of soil dynamic behavior

The response of geomaterials to low-strain dynamic loading is of foremost importance in a variety of situations in soil dynamics (e.g. foundation design of vibrating machines, assessment of vibrational impact induced by railway, subway or roadway traffic) and earthquake geotechnical engineering (e.g. ground response analysis at stable sites). Yet, the current methods to determine the low-strain parameters of soil dynamic behavior are characterized by a number of shortcomings and inconsistencies. Even the very same definition of these parameters is imprecise and in a way contradictory. This has relevant implications when they are used to solve boundary-value problems, particularly through advanced numerical modeling, as it will be shown in the paper. The article, after a critical review of two widespread field and laboratory experimental tests, introduces non-conventional techniques to carry out and interpret the same experiments to measure the low-strain parameters of soil dynamic behavior. The preliminary results obtained from these emerging methods are encouraging despite a few technical difficulties that still need to be overcome.