保水曲線在不同頻率的彈性波影響下之變化研究

An Experimental Study on the Impact of Different-frequency Elastic Waves on Water Retention Curve

鄧教弘(Jiao-Hong Deng) ； 戴嘉佑(Jia-You Dai) ； 李哲瑋(Jhe-Wei Lee) ； 羅偉誠(Wei-Cheng Lo) ； 陳主惠(Chu-Hui Chen)

《農業工程學報》 66卷2期 (2020/06) Pp. 64-75

https://doi.org/10.29974/JTAE.202006_66(2).0006

摘要

近年來彈性波應用在孔彈性介質中之理論研究受到眾多學者的關注，尤其是在含二相或多相非混合流體之孔隙介質中的傳遞特性更引起廣泛討論。目前已經知道彈性波在含二相流體之孔隙介質中傳遞會對土壤保水曲線造成影響，但至今尚未找出保水曲線受彈性波震動頻率影響之特性，也未知彈性波對土壤影響為暫時性或是永久性。本研究以砂箱試驗將砂箱內土壤分為三層（下、中、上層）分別探討3種頻率（150Hz、300Hz、450Hz）的聲波（彈性波）對乾燥過程之保水曲線的影響與聲波影響前後保水曲線之變化，另外再觀察不同深度下的保水曲線受聲波影響之情況。根據實驗結果發現聲波可以使土體產生膨脹或沉陷，當聲波使土體產生膨脹後，土體能以自然沉陷而恢復到聲波影響前之狀態；反之當聲波使土體沉陷後，土體則無法恢復到聲波影響前之狀態，故認定聲波造成土體膨脹為暫時性影響；造成土體沉陷為永久性影響，也從回歸資料中發現形狀因子α 會隨著毛細張力減少而上升，而形狀因子n則會隨毛細張力減少而下降。此外從不同深度之土壤受聲波影響下的實驗結果發現，聲波使土體膨脹或沉陷之程度會因土壤深度不同而改變，但使土體產生膨脹或是沉陷僅取決於聲波之頻率，並不會隨著土壤深度產生交替變化。

關鍵字

彈性波 ； 保水曲線 ； 砂箱試驗

並列摘要

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.

並列關鍵字

Elastic waves ； Water retention curve ； Sand box test