A comparative numerical simulation study of single-phase flow and water-gas two-phase flow infiltration process in the vadose zone with the layered heterogeneous structure
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摘要:
包气带水分入渗过程受多种因素的影响。定量研究层状非均质岩性结构和入渗速率对其影响，有助于解决根据不同条件选择单相流模型或水气二相流模型模拟包气带水分入渗过程的问题。结合填埋场等场地地层条件及污废水入渗特征，分别建立了“上细下粗”和“上粗下细”包气带层状非均质岩性结构水分入渗单相流和水气二相流模型，探讨不同层状非均质岩性结构条件下模型的适用性。在“上粗下细”岩性结构模型基础上，进一步探究入渗速率对水气两相运移结果的影响。基于论文模型研究表明：（1）在包气带岩性结构为“上细下粗”的条件下，气相的影响基本可以忽略，可直接采用单相流模型对包气带水分运移进行模拟；在“上粗下细”岩性结构和本次模型设定的底部压力保持不变及污废水泄漏前场地未接受降水入渗补给等条件下，当包气带上下层介质渗透率比值大于16倍时，气相会对水相运移产生明显影响，且下层介质渗透率越小、上下层介质渗透率比值越大，单相流与两相流的运移结果差别越大，需要采用水气二相流模型模拟包气带水分运移。（2）在包气带“上粗下细”岩性结构条件下，入渗速率越大，气相对水流入渗的阻滞作用越明显，此时包气带水分运移模拟应采用水气二相流模型。
Abstract:The infiltration process in the vadose zone is affected by many factors. A quantitative study of the influence of the layered heterogeneous lithological structure and infiltration rate on the process of water infiltration in the vadose zone is helpful in selecting a single-phase flow model or water-gas two-phase flow model for simulating the infiltration process in the vadose zone under different conditions. In this study, combined with stratum conditions of landfills and other sites and the infiltration characteristics of polluted or waste water, water infiltration single-phase flow and water-gas two-phase flow models are established under the “upper fine and lower coarse” and “upper coarse and lower fine” layered heterogeneous lithological structures of the vadose zone, in order to discuss the applicability of the models under different layered heterogeneous lithological structures. Based on the “upper coarse and lower fine” lithological structural model, the influence of infiltration rate on the results of water-gas two-phase migration is further explored. The results based on paper models show that (1) under the “upper fine and lower coarse” lithological structure condition of the vadose zone, the influence of the gas phase can be ignored and the single-phase flow model can be used to simulate water migration in the vadose zone. Under the settings of the “upper coarseness and lower fineness” lithological structure, the fixed bottom pressure and no precipitation infiltration before the leakage of sewage and wastewater in this model, gas phase has a significant impact on the water migration when the permeability ratio of the upper and lower media in the vadose zone is greater than about 16 times, and the lower the permeability of the underlying medium and the greater the permeability ratio of the upper and lower media, the greater the difference between the results of the single-phase flow and water-gas two-phase flow. It is necessary to use the water-gas two-phase flow model to simulate the water migration in the vadose zone. (2) Under the “upper coarseness and lower fineness” lithological structure condition of the adose zone, the greater the infiltration rate, the stronger the blocking effect of air on the water infiltration, and the water-gas two-phase flow model should be used to simulate the process of water migration in the vadose zone.
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介质 密度/（kg·m−3） 渗透率/（10−12m2） 孔隙度 相对渗透率-饱和度关系曲线
(VG-M模型)毛细压力-饱和度关系曲线
(VG模型)λ Slr Sls Sgr λ Slr Sls Pmax 1/P0 粗砂 2 650 30 0.31 0.416 0.06 1 0.05 0.416 0.06 1 5×106 3.0×10−4 细砂 2 650 8.0 0.35 0.430 0.10 1 0.05 0.430 0.10 1 5×106 2.5×10−4 亚黏土 2 650 0.16 0.40 0.447 0.15 1 0.05 0.447 0.15 1 5×106 1.0×10−4 注：λ为经验参数， 
为残余水饱和度，
为饱和水饱和度，
为残余气饱和度，Pmax为最大吸力，1/
为土壤进气值的倒数。
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表 2 不同模拟情景参数设置
Table 2. Parameter settings of different simulation cases
模拟情景设置 渗透率/（10−12m2） 上下层介质
渗透率比值上层介质（细砂） 8.0 / 情景1 下层介质1
（亚黏土）0.16 50 情景2 下层介质2 0.20 40 情景3 下层介质3 0.40 20 情景4 下层介质4 0.50 16 情景5 下层介质5 0.80 10 情景6 下层介质6 1.6 5
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