在非飽和地下水系統之多相流和傳輸過程研究中，數值模擬為廣泛應用的技術，本研究使用Lawrence Berkeley National Laboratory (LBNL) 所開發之iTOUGH2模式配合實驗室尺度砂箱實驗進行非飽和土壤參數推估。iTOUGH2模式可應用於模擬多孔隙介質或裂隙介質中的多相流(multiphase)、多成分(multi-component)及非等溫(non-isothermal)的水流及溶質傳輸。本研究利用此模式驗證實驗室尺度注氣試驗系統，並進一步利用此模式參數反推估功能，估計 實驗室尺度砂箱內非飽和土壤的氣體滲透性及孔隙率。注氣試驗方法是利用試驗孔中變換注氣孔及觀測孔位置進行量測氣壓力隨時間之變化，由蒐集之觀測數據，輸入iTOUGH2模式中進行參數值之最佳化。透過最佳化之參數模擬結果可提供較高解析度之非飽和土壤參數分布。本研究以模式測試例驗證模式之模擬與反推參數功能，以實驗室尺度一至二維砂箱實驗資料代入模式進行參數反推估，研究結果顯示在模式測試例時，使用模擬之壓力資料可準確的反推估砂樣滲透性與孔隙率，但是在套用實驗室砂箱實驗數據時，以穩態之實驗壓力數據僅可正確地反推估出砂樣滲透性分布；以實驗暫態部分壓力資料反推估孔隙率時，因為實驗初期氣壓變化過快，且實驗使用之流量計取樣速率過慢，所以在孔隙率反推估上有相當的困難性存在。以修正後之實驗數據反推實驗土壤孔隙率，在一維實驗部分可以以修正後之實驗數據反推部分砂樣孔隙率，而二維實驗部分因修正之資料點過多，難以反推孔隙率之分布。The numerical simulation has become a popular technique in studying multiphase flow and mass transport in unsaturated zones of groundwater systems. In the study, we use iTOUGH2 model developed by LBNL to estimate parameters of unsaturated soils. The iTOUGH2 model can be applied to simulate the flow and mass transport with multiphase, multi-component, and non-isothermal conditions in porous medium or fractured medium. This study uses the iTOUGH2 model associated with pneumatic injection tests to inversely estimate the permeability and porosity of lab-scale unsaturated soils on sandbox. The pneumatic test injects air in one location and monitoring the variations of air pressures at other locations in the sandbox. Same injection event is repeated at different injection locations. The sequential pneumatic tests yield a series of air pressure measurements. Such measured data are then used in the iTOUGH2 model to obtain optimal distributions of unsaturated soil parameters, i.e., the permeability and porosity. Simulation results show that the permeability and porosity can be estimated accurately for the synthetic cases. However, only permeability can be estimated with lab-scale sandbox experimental data. There are difficulties in estimating porosity, including the rapidly pressure changes and measurements of accurate gas flow rates and location of observation points mean boundaries.
