近數十年來彈性波在含多相流體的孔隙介質中傳遞行為，引起各界學者研究的興趣，它在工程上的應用具有相當大的價值性。如利用震波預測地下水的相關地質參數，可增加地下水的使用率、低頻彈性波使NAPL(Non Aqueous Phase Liquid, 非水相液體)產生運移來增加地下水汙染整治的效率，亦可提升原油的開採。而高頻彈性波(超音波)則運用在生物工程上，可用來偵測骨骼和軟骨組織的特性及變異。而本研究所探討的「壓力波」，屬於彈性波的一種，其質點運動方向與傳波方向平行。
而保水曲線(Water Retention Curve)是彈性波波傳行為中重要的影響因子之一，過去總以保水曲線之性質不變下，來探討水份變化或者土壤體積變化的關係，但始終未考慮保水曲線是否會受到彈性波的影響而產生變化。故本研究將利用砂箱試驗來探討在壓力波作用下，保水曲線本身是否會受到影響。
本研究利用渥太華標準砂(C109)當作實驗土體，在得到相關土壤特性參數後，利用循環水位升降砂箱試驗，以模擬真實自然界的溼潤與乾燥過程，而得到張力水頭與體積含水比，繪製成保水曲線。待曲線穩定後，分別探討6種頻率(100Hz、150Hz、200Hz、250Hz、300Hz和350Hz)之聲波影響下保水曲線的變化，並利用van Genuchten (1980)模式得到相關參數，進而了解壓力波對保水曲線之影響行為。
由實驗結果得知，壓力波確實會影響保水曲線，但並非同一頻率會同時影響保水曲線之溼潤與乾燥過程。其中，在聲波頻率150Hz對於乾濕過程皆有較大的影響；而聲波頻率200Hz對乾燥過程影響較大；反之聲波頻率250Hz在濕潤過程影響較大。相對於未受到壓力波影響下之保水曲線(又為基準保水曲線)的上方或下方，形狀因子 相對於基準保水曲線的形狀因子 值則會偏小或偏大。

Over the past decades, there have been growing research interests in studying the propagation and attenuation of elastic waves through a porous medium bearing two immiscible viscous compressible fluids because of its practical applications of engineering, such as the enhancement of both oil reservoir production and groundwater contaminant removal induced by low-frequency vibrations, and the detection of defects of bone and cartilage using high frequency (ultrasound) energy. Acoustic wave is one of elastic waves whose particle motion direction parallels to its propagation direction.
Water retention curve has been long recognized as one of the important factors that give an influence on the propagation and attenuation of acoustic waves. In the past, variations in water content and soil volume caused by acoustic waves always were studied under the assumption that water retention curve remains unchanged. In this study, sandbox test is carried out to investigate if water retention curve varies due to acoustic effect.
Ottawa sand (C109) is used in this study as an illustrative example. At first, soil properties are measured and then an experiment is conducted by recycling water level of sand box to simulate the imbibition and drainage processes of water retention curve based on the recorded tension head and volumetric water content. When water retention curve remains stable, six different excitation frequencies (100Hz, 150Hz, 200Hz, 250Hz, 300Hz and 350Hz) are selected to examine the effete of acoustic waves, in which the van Genuchten (1980) model is applied to fit experimental data for describing water retention curve.
Our experiment result indicates that water retention curve is indeed affected by the introduction of acoustic waves. However, it is found that not all acoustic waves simultaneously offer an effect on the imbibition and drainage processes of water retention curve. It is revealed experimentally that acoustic wave with excitation frequency of 150Hz renders an impact on the imbibition process and drainage process, acoustic wave with excitation frequency of 200Hz has the most significant impact on the drainage process, and acoustic wave with excitation frequency of 250Hz has the most significant impact on the imbibition process. It is also shown that if water retention curve moves upward, the shape factor is observed to be smaller, while if water retention curve moves downward, we find that the shape factor would be greater.

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