Nonlinear acoustic behaviors of soils

Soil, like other porous materials such as rock, sand, sandstone, sedimentation, and concrete, exhibits remarkable nonlinear behaviors. In this work, the nonlinear acoustic behaviors of soils are studied by measuring both amplitude and phase frequency responses as a function of dynamic strain. Typical nonlinear phenomena such as resonant frequency shift and harmonics generation are observed. It is also found that the phase difference between the received and reference signals changes with strain. New methods for measuring the nonlinearity parameters, based on resonant frequency shift, phase shift, and phase slope measurements, are developed and compared. This suggests that phase could be a very useful parameter for determining the nonlinearity of porous materials. [This work is supported by the USDA Agricultural Research Service under Specific Cooperative Agreement 58‐6408‐0‐108.]