Air Entry Barriers: Mechanism for Creating High Permeability Pathways Above the Water Table

0087228 Silliman大量文献证明了从渗流带到地下水位及以下区域的过渡带的重要性，该过渡带以毛细边缘为主。 然而，已经有最小的研究流动和运输机制的相互作用，在整个过渡区一般，特别是在毛细管边缘。 这里假设，异质性将导致独特的流动，运输和地球化学特性的过渡区内的相关，部分，低气相渗透率，可以存在于高水分含量。 空气进入壁垒（AEBs）和其他流动和运输障碍可能会在细颗粒的情况下形成， 覆盖在粗粒沉积物上 在排水过程中，可以防止空气进入被细颗粒覆盖的粗颗粒沉积物。 在吸入过程中，空气可能被困在被细粒覆盖的粗料区域内。 这种对空气相运动的限制将对过渡带的水流、化学输运、地球化学和微生物产生重大影响，并随着时间的推移受到这些因素的影响。中心假设是，由于AEB的存在，ZT内粗颗粒沉积物中的水分含量、水力传导率以及流体和化学物质的通量将取决于：（a）粗粒沉积物内的孔隙水压力，（B）粗粒沉积物的连续性，（c）周围细粒沉积物的位置和连续性，（d）相对于粗颗粒沉积物和周围较细颗粒沉积物的地下水位波动历史，和（e）含水量的初始分布。 这一假设将通过实验室实验来解决， 在均匀介质中，以及在交替地由简单层、互连层和嵌入在细粒度部分中的粗粒度部分的不连续透镜组成的介质中的流动和传输。 孔隙水压力和测得的含水量之间的差异，加上优先流动路径的观察，将用于识别AEB的存在。

0087228SillimanA substantial body of literature exist which demonstrates the importance of the zone of transition, dominated by the capillary fringe, from the vadose zone into the region at and below the water table. However, there has been minimal study of the interplay of flow and transport mechanisms across this zone of transition in general, and specifically within the capillary fringe. It is here hypothesized that heterogeniety will lead to unique flow, transport and geochemical characteristics within the zone of transition related, in part, to low gas-phase permeabilities that can be present at high moisture contents. Air Entry Barriers (AEBs)and other impediments to flow and transport may form in situations in which fine-grained overlie coarse-grained sediments. During drainage, air may be prevented from entering coarse-grained sediments that are overlain by fines. During imbibition, air may be trapped within zones of coarse material overlain by fines. Such restriction on the movement of the air phase will have significant effect on and over time be affected by water-flow, chemical transport, geochemistry and microbiology in the zone of transition.The central hypothesis is that due to AEBs, the moisture content, hydraulic conductivity, and flux of fluid and chemicals within coarse-grained sediments within the ZT will depend on: (a) the pore water pressure within the coarse-grained sediments, (b) the continuity of the coarse sediments, (c) the position and continuity of the surrounding finer-grained sediments, (d) the history of fluctuation of the water table relative to both the coarse-grained sediments and the surrounding finer-grained sediments, and (e) the initial distribution of moisture content. This hypothesis will be addressed through laboratory experiments on flow and transport in homogeneous media, and in media consisting alternatively of simple layers, interconnected layers, and disconnected lenses of the coarse size fraction embedded within a fine size fraction. Discrepancy between pore water pressure and measured moisture contents, plus observation of preferential flow pathways will be used to identify the presence of AEBs.