We examined the effects of acoustic excitations on the water retention curve, i.e., the relationship between capillary pressure
(PCtrue) and water saturation
true(SWtrue) in unsaturated porous media, during drainage. The water retention curves were measured under static and dynamic conditions, where water was withdrawn from a sandbox with three different pumping rates, 12.6, 19.7, and 25.2 mL/s. Excitations with frequencies of 75, 100, 125, and 150 Hz were applied. The acoustic excitations had no effect on the static water retention curve but altered the dynamic water retention curve. The acoustic excitations lowered the dynamic
PC, especially under the dynamic condition where the pumping rate was 25.2 mL/s and when
SW varied between 0.6 and 0.95. The differences between the capillary pressures measured under static and dynamic conditions decreased when acoustic excitations were applied. We link this finding to the change in contact angle induced by the acoustic excitation. The dynamic coefficients,
τ, for the dynamic water retention curves that we fitted to the experimental data were smaller with than without acoustic excitations. We attribute the decrease of the dynamic coefficient to the combination of the increase in the permeability and the decline in the air‐entry pressure caused by adding acoustic excitations.
[1] A viscoelastic model is developed to simulate the groundwater level changes in the Cho-Shui River alluvial fan in Taiwan after the Chi-Chi earthquake. An analytical solution is derived with the assumption that no leakage occurred in confined aquifers during the coseismic period. The solution is used to analyze the data collected from a high-density network of hydrologic monitoring wells in the Cho-Shui River alluvial fan. The simulated groundwater level changes agree with the observations. The viscosity coefficient of the model was found to correlate with the hydraulic conductivity of the aquifer. The field observations and the simulations reveal the influence of geological structures and heterogeneity on the groundwater changes and locations of sediment liquefactions in the alluvial fan during the Chi-Chi earthquake. Possible applications to imaging subsurface hydraulic heterogeneity are discussed using information about groundwater level changes induced by earthquakes.
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