Monitoring of Phase Transition in Frozen Soil Using the Nonlinear (SPC-1) Ultrasonic Technique

Frozen soils constitute a significant amount of land's surface and are responsible for the (global) energy balances and heat transfer mechanisms affecting both land and atmospheric processes. Characterization and measurement of the properties of frozen soils during phase transition (frozen to unfrozen) is a challenging problem vowing to heterogeneity in ice-lens formation, unfrozen water, and pore structure configuration of soil grains. This study presents a non-linear ultrasonic (NLU) technique called the sideband peak count-index (SPC-I) in combination with the linear ultrasonic (LU) technique to monitor the phase transition (frozen to unfrozen) of frozen soil specimens. Earlier studies using nondestructive testing and evaluation (NDT&E) have demonstrated the use of LU and NLU techniques to detect defects such as micro-cracks, however, there are no studies performed to evaluate the use of this approach to quantify the non-linearity in frozen soils during their phase transitions. The general approach of applying the SPC-I technique is by transmitting and analyzing a single excitation signal that is propagated through the frozen soil specimen. In this study, the clayey sand soils are considered for evaluating the non-linear behavior of the soils during the phase transition process (frozen to unfrozen). These soils can undergo significant frost-heave and thaw-weakening phenomena resulting in infrastructure distress including potholes, differential settlements, slope failures, and thawing-induced landslides. In the United States approximately 2 billion dollars were spent annually to just repair the highway infrastructure distress caused due to freeze-thaw cycles and better characterization approaches are required to understand the behavior of this non-linear geomaterial. The NLU SPC-I technique combined with LU technique could robustly detect the changes in material properties of frozen soil, however, it can be further tuned and improved by exciting a tuned excitation signal.