未飽和緩衝材料吸力與水力傳導度推求及再飽和行為

Soil suction, hydraulic conductivity, and resaturation behavior of unsaturated buffer material

莊怡芳(Yi-Fang Chuang)

指導教授 ： 黃偉慶

國立中央大學/工學院/土木工程學系/碩士(2008年)

摘要

國際間核能先進國家對於高放射性廢棄物處置，皆以多重障壁深地層處置為主，而緩衝材料屬多重障壁包覆廢棄物之主要安全貢獻因子之一，因處置場位於地下數百公尺處，必定遭受地下水入侵之影響，而緩衝材料因包覆於廢棄物罐外，亦受到放射性廢棄物釋放衰變熱影響。本研究利用有限元素程式，模擬緩衝材料受地下水入侵與溫度影響下之含水量分佈，以土壤吸力與未飽和水力傳導度之觀念掌握緩衝材料之再飽和行為，利用水汽平衡試驗量測BH膨潤土與日興土於不同溫度下之土壤吸力土壤吸力與含水量關係，並利用土壤-水份特性曲線推估模式，取得完整飽和過程之吸力變化。土壤於未飽和狀態下之水力傳導度將隨含水量而變化，本研究將於土壤-水分特性曲線之基礎下計算不同飽和度下之水力傳導度值。接著利用實驗所得之參數，應用於有限元素程式模擬緩衝材料攝水行為。
吸力試驗結果得知，土壤吸力會因環境溫度升高而降低，且BH膨潤土之吸力範圍大於日興土。土壤接近乾燥之吸力量測結果，亦顯示土壤於接近乾燥時之吸力將達106 kPa。實驗參數套用於程式模擬結果多近於實驗值之趨勢，可合理模擬土壤於不同溫度下之攝水行為。

關鍵字

緩衝材料 ； 土壤-水份特性曲線 ； 未飽和水力傳導度

並列摘要

Deep geological disposal is considered by many countries as a feasible way for the final disposal of high-level radioactive wastes. Buffer material plays a major role for the isolation of radioactive wastes in an underground repository. This research investigates the unsaturated hydraulic conductivity and resaturation behavior of buffer material, with emphasis on the effects of soil suction of buffer material on the groundwater intrusion processes and the temperature effect. Soil suction of Zhisin clay and Black Hill (BH) bentoite were determined using vapor equilibrium technique on clay specimens so as to determine the relationship between soil suction and water content. Soil-water characteristic curve was fitted with the Fredlund model such that the hydraulic conductivity of clays in unsaturated conditions can be estimated. The finite element program ABAQUS was then employed to carry out the numerical simulation of the resaturation process in the near field of a repository.
The results show that soil suction of BH behtonite is higher than Zhisin clay, and soil suction was found to decrease as the temperature increases. At a dry state, the soil suction will reach a maximum suction of 106 kPa. Results of the numerical simulation were validated using the degree of saturation profile obtained from the water uptake test on the two clays. The unsaturated behavior of highly plastic bentonite material shows important effects on the saturation behavior of the material.

並列關鍵字

soil-water characteristic curve ； unsaturated hydraulic conductivity ； buffer material

參考文獻

Burdine, N. T. (1953). “Relative permeability calculations from pore-size distribution data.” Petrol. Trans., Am. Inst. Min. Eng., Vol. 198, pp.71-77.

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Delage, P., Howat, M. D., and Cui, Y. J. (1998). “The relationship between suction and swelling properties in a heavily compacted unsaturated clay.” Engineering Geology, Vol. 50, pp. 31-48.

Fredlund, D. G., and Xing, A. (1994a). “Equations for the soil-water characteristic curve,” Canadian Geotechnical Journal, Vol. 31, pp. 521-532.

Fredlund, D. G., Xing, A., and Huang S. (1994b) “Predicting the permeability function for unsaturated soil using the soil-water characteristic curve.” Canadian Geotechnical Journal, Vol. 31, pp. 533-546.