基于ERT和模型技术的地下水AS扰动机理研究

发布时间：2018-02-28 17:08

本文关键词： 地下水空气扰动(AS) 高密度电阻率法(ERT) 空气流型空气流动模型　出处：《吉林大学》2016年硕士论文　论文类型：学位论文

【摘要】：地下水空气扰动(AS)是一种新兴污染地下水原位修复技术,该技术被认为是去除非饱和区带土壤和浅层地下水中挥发性有机污染物的最有效方法之一,其优势在于成本低、效率高、可操作性较强。但是关于污染场地AS处理过程中的物理、化学、生物及复合作用的相关机理尚不明晰,地下水空气扰动修复系统相关设计参数多为经验估计,而对于AS运行作用机制的理论研究更不完善。地下水空气扰动AS修复过程中,空气在饱和多孔介质中的流动机制及影响范围是污染地下环境中修复效率的主要影响因素。传统的空气扰动影响区域(ZOI)监测方法为场地布井实验,一般依赖于钻井、样品溶解氧测定和地下水位监测等手段,监测成本高、人员需求量大、监测反应速度较慢、不宜考虑非均质介质,同时对场地的土地利用带来了不可忽视的破坏性扰动。因此,本文以高密度电阻率法(ERT)这一无损的非扰动地电学勘探方法为主要手段,构建该方法在地下水空气扰动监测中的应用路径,并以多相流体力学为理论基础对AS进行研究,建立了二维实验砂槽中不同粒径均质玻璃珠(GBS)饱和介质中空气流动模型。本文采用高密度电阻率法(ERT)为主要监测手段,通过控制多孔介质材料分选性、粒度级配、空气扰动流量等室内实验变量,对AS气体流型、范围及空气饱和度动态分布进行研究。结果表明,高密度电阻率法(ERT)在AS监测中具有很好的灵敏度及准确性,且测试较为方便快捷。介质中空气扰动压力与气体流量呈线性正相关关系;分选性较好的均质介质中气体饱和度以曝气口中心所在横截面对称分布,中心饱和度较大;非均质中气体遇到渗透性小的区域时气体会聚集,并选择少数通道优先通过。曝气流量较大时,气体易横向漂移,局部优先流容易形成。同时,在不同粒径的均匀介质中,空气扰动范围主要受空气扰动注气流量及压力影响,与粒径无关,但气流形式受粒径影响。3 mm均匀玻璃珠介质中,气体以气泡形式向上运动;1 mm均匀玻璃珠介质中气体流动方式为微通道式;0.5 mm均匀玻璃珠介质中,气体仍以微通道形式运动,但气流通道相对分散且弯曲。而在非均匀介质中,气体主要为槽式流,以块区域形式出现。以室内实验条件构建物理模型,在Darcy定律和Bessel函数理论变换基础上,结合水土特征曲线中的Fredlund和Xing(FX)模型与van Genuchten(VG)模型,本文提出了二维砂槽实验条件下的AS轴对称空气流动模型,并利用室内AS实验对该模型进行验证。
[Abstract]:Groundwater air disturbance (ASA) is a newly developed in situ remediation technology for polluted groundwater, which is considered to be one of the most effective methods to remove volatile organic pollutants from unsaturated zone soil and shallow groundwater. Its advantage lies in its low cost. However, the mechanism of physical, chemical, biological and compound action in the process of as treatment of contaminated site is not clear, and the related design parameters of groundwater air disturbance remediation system are mostly estimated by experience. However, the theoretical study on the mechanism of as operation is far from perfect. In the process of groundwater air disturbance as remediation, The flow mechanism and influence range of air in saturated porous media are the main influencing factors of remediation efficiency in polluted underground environment. By means of sample dissolved oxygen determination and groundwater level monitoring, the cost of monitoring is high, the demand for personnel is large, the monitoring reaction is slow, it is not appropriate to consider heterogeneous media, and at the same time, it has brought a destructive disturbance to the land use of the site. In this paper, the high density resistivity method (ERT), a non-perturbed geoelectric exploration method, is used as the main means to construct the application path of this method in the monitoring of groundwater air disturbance, and based on the theory of multiphase hydrodynamics, as is studied. A model of air flow in saturated medium with different sizes of homogeneous glass beads in a two-dimensional experimental sand tank is established. The high density resistivity method (ERT) is used as the main monitoring method to control the material sorting and particle size gradation of porous media. The dynamic distribution of as gas flow pattern, range and air saturation are studied by using indoor experimental variables such as air disturbance flow rate. The results show that the high density resistivity method has good sensitivity and accuracy in as monitoring. The air disturbance pressure in the medium has a linear positive correlation with the gas flow rate, and the gas saturation in the homogeneous medium with good sorting is symmetrical distribution in the cross section of the aeration center, and the center saturation is larger. When the gas in heterogeneity meets the low permeability area, the gas accumulates and chooses a few channels to pass first. When the aeration rate is high, the gas tends to drift laterally, and the local preferential flow is easy to form. At the same time, in the homogeneous medium with different particle sizes, The range of air disturbance is mainly affected by the gas injection rate and pressure of air disturbance, which is independent of the particle size, but the air flow pattern is affected by the particle size in the homogeneous glass bead medium. The gas moves upward in the form of bubbles in a 1 mm uniform glass bead medium. The gas flow pattern is in the microchannel type of 0.5 mm uniform glass bead medium. The gas still moves in the form of a microchannel, but the airflow channel is relatively dispersed and curved, while in the non-uniform medium, The gas is mainly a trough flow and appears as a block region. Based on the experimental conditions in laboratory, the physical model is constructed. Based on the transformation of Darcy's law and Bessel's function theory, the Fredlund and Xingfx models in the soil and water characteristic curves are combined with the van Genuchtene VG model. In this paper, an as axisymmetric air flow model under the condition of two-dimensional sand tank experiment is proposed, and the model is verified by laboratory as experiment.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X523

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