Evolution of Small Strain Soil Stiffness during Freeze-Thaw Cycle: Transition from Capillarity to Cementation Examined Using Magnetic and Piezo Crystal Sensors

Abstract

Freeze-thaw cycles caused by seasonal temperature fluctuations significantly affect the geotechnical engineering properties. This study investigated the crucial role of water distribution patterns in the characterization of elastic wave properties for the fine F-110 sand during a freeze-thaw cycle. Sand specimens with four different water distribution patterns were prepared, namely homogeneously-mixed, evaporation-driven, vertically-, and horizontally-layered specimens. The P- and S-wave signatures of the specimens were monitored using piezo crystal sensors. Results indicated the criticality of water distribution patterns in the determination of small-strain soil properties even though the specimens had identical global water saturation. The nuclear magnetic resonance-based water volume depth profiles indicated that the evaporation-driven specimens had more heterogeneous pore-invasive ice-bonding layers at a high water saturation region; by contrast, the drying process facilitated uniform meniscuses around the particle contacts near the air percolation threshold. Elastic wave measurements for laboratory-prepared specimens might over/underestimate the small-strain soil stiffness of sediments in nature, wherein the drying processes prevailed to control the water saturation. This study highlighted a clear transition from capillary-controlled to cementation-controlled elastic wave properties during temperature oscillations.

A Freezing-Thawing Damage Characterization Method for Highway Subgrade in Seasonally Frozen Regions Based on Thermal-Hydraulic-Mechanical Coupling Model

“…According to the Gibbs–Thomson effect [ 30 , 31 , 32 , 33 ], there is still unfrozen water inside the subgrade even in a frozen zone at a temperature that is below the bulk freezing point of water (0 °C), and the unfrozen water in either the frozen zone or the thawing zone meets Darcy’s law. Based on the Richards equation [ 34 ], considering the blocking effect of pore ice in frozen soil, the governing equation of water transport in unsaturated soil with unfrozen water content as an independent variable can be expressed as [ 35 ]: where is volumetric content of unfrozen water, and the total volumetric water content is expressed as .…”

Effect of water distribution patterns on the activation energy of unsaturated soils during phase transformation

“…The particle-level view describes the water meniscus among the particles of the various water distribution patterns. The homogeneously mixed and evaporation-driven specimens exhibited an identical global water distribution pattern (at least for saturation S = 30%), whereas they exhibited different water meniscus between the particles (see the nuclear magnetic resonance [NMR] results in Park et al, 2021) at two consecutive temperatures during a freezing process. For example, V p measured at T 1 = −1 ˚C corresponded to K 1 , and V p measured at T 2 = 0 ˚C corresponded to K 2 (Equation 3).…”

“…This section briefly describes the experimental method and conditions for the determination of the elastic wave velocities gathered from the published study by Park et al (2021). They measured the P-and S-wave velocities (V p and V s , respectively) of unsaturated soils during a freeze-thaw cycle.…”

“…(a) P-wave velocity, V p , at a saturation degree, S, of 30%; (b) S-wave velocity, V s , at S = 30%; (c) V p at S = 60%, and (d) V s at S = 60%. Note: data were obtained from the reports of Park et al (2021) Partially saturated layers were observed at the boundaries between the dry and saturated layers in the vertically and horizontally layered specimens, which resulted from the migration of water due to gravity and adhesion. However, these transition layers can be assumed to be thin and uniform-shaped because of the capillary forces of fine sand.…”

“…Figure 2 shows the plots of the V p and V s of the unsaturated sand specimens (at S = 30 and 60%) with different water distribution patterns, including homogeneously mixed, evaporation-driven, vertically layered, and horizontally layered arrangements (note: data reported in the study by Park et al, 2021). The minimum energy required for freezing and thawing processes was assumed to be similar; therefore, this study analyzed the E a during the freezing process.…”