【作者】 刘燕；

【导师】 胡黎明；

【作者基本信息】 清华大学 ， 土木工程， 2009， 硕士

【摘要】 挥发性有机污染物是土壤和地下水中的重要污染物,发展土壤和地下水修复技术对人类环境的可持续发展具有重要的意义。地下水曝气法是有效的土壤地下水修复技术。本文采用不同粒径级配的高强度喷丸玻璃珠模拟自然砂土,进行了常规模型试验和离心模型试验,研究了曝气过程中的气体运动规律,分析了曝气压力与气体流量、单井影响区域的关系。本文取得了如下研究成果:1.常规模型试验和离心模型试验研究表明:1)多孔介质粒径级配决定气体的运动方式,颗粒粒径较大时气体以独立气泡方式运动,粒径较小时气体以离散的微通道方式运动;试样孔隙的不均匀性会影响气体的运动方式。2)单井影响区域形状与粒径、曝气压力等因素无关,为锥面形;而曝气影响区域大小受粒径、曝气压力等因素的影响明显,粒径越大,曝气影响区域越小;存在曝气压力临界值,达到该值之前,影响区域随曝气压力增大而增大,曝气压力达到该值后,影响区域大小趋于稳定。3)与试验中实测的曝气压力值相比,过去研究者提出的理论计算公式确定的最大曝气压力值偏低,需要修正。4)粒径级配、曝气压力等因素对气体流量有显著的影响,气体流量随曝气压力的增大而增大。5)地下水曝气过程中气体优势流现象和曝气区域附近水面隆起现象明显。2.提出采用最大渗气夹角和理论曝气点描述最大曝气影响区域的大小,认为最大影响区域是以理论曝气点为圆锥顶点、与竖直方向呈一定夹角的圆锥体区域,该方法简单易行,对不同粒径级配的均匀土层均适用。3.常规模型试验还研究了曝气过程中试样平均饱和度的变化以及试样的非均匀性对曝气过程的影响,试验结果表明:曝气试验前后,试样曝气影响区域内的平均饱和度变化受粒径、曝气压力等因素影响很小;试样的非均匀性对单井影响区域有显著影响。4.离心模型试验还研究了不同离心加速度对曝气过程的影响,试验结果表明:离心加速度越大,均匀试样中气体流量越大,气泡在土体中的运动速度越大,单井的曝气影响区域越小。曝气过程中的离心模型相似比有待于进一步深入研究。更多还原

【Abstract】 Development of efficient techniques to remediate soils and groundwater contaminated with voltaic organic compounds is of great importance to sustainable development of human environment. Air sparging is one of themost efficient techniques. In this thesis, the physical mechanism of air sparging process is investigated by means of conventional modeling tests and centrifuge modeling tests using glass beads with different diameters of 0.8-1.0 mm、1.5-2.0 mm、4.0-5.0 mm and 0.8-5.0 mm as a substitute for sands. The features of air flow during sparging process are observed, and the effect of air pressure on air flow rate and zone of influence are studied systematically.The main achievements are summarized as follows:1. Conventional model tests and centrifuge model tests show that: 1) air flow patterns in porous media are determined by grain size distribution, e.g., air flows in discrete micro-channels in fine grain media but travels in bubbles in coarse media; air flow patterns are also influenced by inhomogeneity of distribution of pores; 2) the shape of zone of influence is always a cone in uniform porous media; the area of the cone is affected by grain size and sparging pressure obviously, i.e., the larger the diameter, the smaller the zone; there exits a critical sparging pressure, below which the zone of influence (ZOI) keeps enlargingwith the increase of sparging pressure, and exceeding which the ZOI tends to be steady; 3) the maximum sparging pressure calculated from equation proposed by the previous researchers is not agreeable with the experimental findings, and need to be modified; 4) air flux is significantly affected by grain size distribution and sparging pressure, e.g., air flux increases with the improvement of grain size and sparging pressure; 5) there are obvious preferential flow during sparging process and water mounding around the sparging area.2. The maximum sparging angle and the vitual sparging point can be used to quantificationally describe the zone of maximum influence, which is considered to be a cone with theoretical sparging point as the vertex This method is quite convinient and can be applied to uniform soil mass with different grain size.3. The average saturation inside ZOI is investigated during conventional modeling tests, and it is shown that the change of average saturation in effecting area is rarely affected by grain size and sparging pressure. The inhomogeneity of samples can significantly affect the zone of influence.4. The effects of centrifugeacceleration on sparging process are studied during centrifuge modeling tests, and it is shown that the greater the acceleration, the larger the air flux and bubble velocity, and the smaller the zone of influence. Scaling factors of centrifuge tests for air sparging process needs to further investigation.更多还原