Physical Modeling On Air Sparging Technique

Air sparging is one of the most efficient techniques to remedy saturatedsoils and groundwater contaminated by voltaic organic compounds.In thisthesis, conventional model tests and centrifuge modeling tests were performedto investigate air flow mechanism under2D conditions, using glass beads withdifferent diameters of0.08-1.0mm,0.8-1.0mm,1.5-2.0mm,4.0-5.0mm and5.0-6.0mm to simulate fine sand. Based on conventional modeling tests andcentrifuge modeling tests, air flow patterns were observed and analyzed todetermine the impact of the sparging pressure, g-level, grain size, layerthickness and the direction of sparging on air flow rate and the zone ofinfluence (ZOI).Model tests of glass beads with different grain size distribution show that:air flow patterns are determined by grain size distribution. If the diameters ofsamples are smaller than0.1mm, air traveled as discrete micro-channels,while the diameters of samples are larger than1.5mm, air traveled as bubbles.The shape of zone of influence is always a truncated cone in conventionalmodel tests and centrifuge modeling tests, and ZOI can be described by coreangle and lateral expansion. The ZOI changes with sparging pressure and afterthe sparging pressure reaches the critical value the ZOI becomes steady. Withthe same g-level, air mass flow rate increased with effective sparging pressureand the effective sparging pressure with air mass flow rate relationship wasessentially bilinear. The slope of the curve have a break, and the slope of coreangle to effective sparging pressure also have a break. We can find thephenomena of “the effective sparging pressure of breaks is the same”. TheZOI and air mass flow rate are governed by g-level, sparging pressure andgrain size. The larger g-level and grain size are, the larger air flow rate andthe slope of air flow rate to effective pressure are; but also a sharper ZOI. The zone of influence under2D conditions is wider than the zone under3Dconditions.In non-homogeneous media, the air mass flow rate is mainly influencedby the fine sized particles. With the increase of g-level, buoyancy becomes themain factor governing the air transport in the media.About ratio of similitude of the centrifuge modeling tests, the ratio of theair mass flow rate per unit width is1:1. We akso find the ratio of the airtransudatory rate “M” is N, and if the ratio of effective sparging pressure toeffective stress of the sample is the same, the ZOI of the sample is also thesame.