An experimental study on the impact of different-frequency elastic waves on water retention curve

Over the past few decades, theoretical and experimental studies on the connection between elastic wave attributes and the physical properties of a fluid-bearing porous medium have attracted the attention of many scholars in fields of porous medium flow and hydrogeology. It has been previously demonstrated that the transmission of elastic waves into a porous medium containing two immiscible fluids will have an effect on the water retention curve, but it remains elusive how the water retention curve will be affected by the frequency of elastic vibration waves or whether the effect on the soil is temporary or permanent. This research is based on a sand box test in which the soil is divided into three layers (lower, middle, and upper layers). In this case, we discuss different impacts on the water retention curve during the drying process under sound waves (elastic waves) subject to three frequencies (150Hz, 300Hz, and 450Hz), respectively. The change in the water retention curve before and after the effect is then discussed. In addition, how sound waves affect the water retention curve at different depths is also observed. According to the experimental results, we find that sound waves can cause soil either to expand or to contract. When the soil is induced to expand due to sound waves, it can contract naturally and return to the condition it was before the influence of the sound waves. On the contrary, when the soil is induced to contract, it is unable to return to its initial condition. Based on the results discussed above, it is suggested that sound waves causing soil to expand have a temporary impact while those causing soil to contract have a permanent impact. In addition, our experimental results show how sound waves affect the water retention curve at different depths. The degree of soil expansion and contraction caused by the sound waves is different at various soil depths. Nevertheless, the expanding or contracting of soil is only subject to the frequency of sound waves. These changes are not altered as different soil depths.