排水過程中土壤保水曲線於動態效應影響之探討

The Study of Dynamic Effect on the Soil Water Retention Curve During the Drainage

曾燕翔(Yen-Hsiang Tseng) ； 邱永嘉(Yung-Chia Chiu)

《農業工程學報》 63卷1期 (2017/03) Pp. 50-58

https://doi.org/10.29974/JTAE.201703_63(1).0007

摘要

未飽和層土壤為一複雜的多相流系統，欲對於層內之水文特性有所瞭解，首要目標即針對水力傳導係數進行測量。水力傳導係數主要透過靜態(static)下的土壤保水曲線(soil water retention curve)進行間接推估，然而，靜態下的保水曲線無法真實反應動態(dynamic)的現地環境。為瞭解動態效應對於土壤保水曲線的影響，本研究透過砂箱實驗，在排水的過程中，研析動態與靜態下所描繪土壤保水曲線的差異。實驗結果顯示，在同一飽和度(saturation)情形下，動態的保水曲線其毛細壓力將大於靜態的毛細壓力，隨著流速或水頭差增加時，其毛細壓力亦逐漸增加。動態因子會隨著飽和度增加而變小，亦會受到土壤顆粒大小的影響。經由本研究之成果得知，雖然動態效應所造成保水曲線差異的機制尚未完全釐清，其對土壤保水曲線的影響確實存在，未來在水力傳導係數量化分析時，動態效應需予以考慮。

關鍵字

未飽和層 ； 土壤保水曲線 ； 毛細壓力 ； 含水量 ； 動態因子

並列摘要

Unsaturated zone is a very complicated multi-phase system. In order to understand the hydrological characteristics in the unsaturated zone, the primary object is to obtain the hydraulic conductivity. Previous studies showed that the hydraulic conductivity could be estimated based on the soil water retention curve. Traditionally, the soil water retention curve is obtained under static condition; however, the static condition does not apply to the field and the dynamic effects should be considered. In this study, a series of laboratory experiments were performed to measure soil water retention curves during the drainage and to assess the significance of dynamic effects on the curves. The experimental results show that the water retention curves can be significantly differentiated under different flow and boundary conditions. At a given water content, the dynamic capillary pressure is higher than the static capillary pressure during the drainage and the difference increases with the increase of flux or head difference. Dynamic coefficient decreases as the increase of saturation, and depends on the grain size of porous media. Although the mechanisms of dynamic effects are unclear, their effects on the water retention curve cannot be ignored and should be considered when quantifying the hydraulic conductivities.

並列關鍵字

Unsaturated zone ； Soil water retention curve ； Capillary pressure ； Water content ； Dynamic coefficient