土壤水分特性曲線(soil-water characteristic curve, SWCC)對於非飽和土壤來說是非常重要的特性函數,此函數關係為特定基質吸力下所對應之體積含水量,對於土壤之水力行為有相當重大之影響。本研究針對台灣之新竹、南投、苗栗、嘉義地區中不同性質土壤進行土壤水份特性曲線試驗(SWCC),但由於試驗過程耗時又費力,因此有學者提出較經濟的模型去預測SWCC,本研究搭配前人之試驗共約185個試驗樣本建立台灣部份地區之SWCC資料庫,並以四位學者(Burdine, 1953、Gardner, 1956、van Genuchten, 1980、Fredlund and Xing, 1994) 所提出之不同預測方法來進行不同土壤性質之SWCC預測,分析結果以van Genuchten (1980) 較能充分擬合試驗樣本,但其缺點為無法擬合基質吸力為106而含水量為0之試驗點。 另外,亦有學者提出利用容易測定之土壤基本性質(例如,粒徑分佈、單位重、比重等)之間接方法預測SWCC,此方法稱為土壤轉換函數(pedo-transfer function, PTF),本研究以六位學者(Gupta and Larson, 1979、Vereecken et al., 1989、Scheinost et al., 1997、Zhuang et al., 2001、Fredlund et al., 2002、Aubertin, 2003) 提出之不同方法來進行不同土壤性質之SWCC預測並將其所有預測結果與試驗結果進行比較及討論。在所有預測模型中,以Gupta and Larson PTF (1979) 較能充分擬合本研究之試驗樣本,且其中就Fredlund et al PTF (2002) 之預測模型,由於本研究樣本數量不一致,導致此模型對於大多數樣本配適不佳,但對於樣本數最大之SM土壤,配適能力頗佳。
Soil water characteristic curve (SWCC) is an important function of unsaturated soil. It defines the volumetric water content corresponding to a particular suction in the soil. Experimental derivation of SWCC is time consuming and, hence, many scholars proposed simple models to back analyze SWCC. The models available are Burdine (1953), Gardner (1958), van Genuchten (1980), Fredlund and Xing (1994), etc.. In additional, there are also functions proposed to estimate SWCC from available soil properties such as particle-size distribution, bulk density, void rate and liquid limit. These estimation functions were referred to as pedo-transfer function (PTF) and some of the examples are Gupta and Larson (1975), Vereecken et al. (1989), Fredlund et al. (1997), Scheinost et al. (1997), Zhuang et al. (2001), and Aubertin (2003). In this study, we back analyzed the SWCC of some 185 soil specimens of different textures using the above four simple models and found that van Genuchten (1980)’s model performed best among the four models. The above six PTFs were also used to estimate the SWCC of the soil specimens. Of all PTFs, we find that Gupta and Larson PTF (1979) is the best PTF model to fit our sample.