SOIL PERMEABILITY OF AERATION ZONE IN XINCHANG-XIANGYANGSHAN- A PRESELECTED SITE FOR HIGH LEVEL RADIOACTIVE WASTE DISPOSAL
SOIL PERMEABILITY OF AERATION ZONE IN XINCHANG-XIANGYANGSHAN- A PRESELECTED SITE FOR HIGH LEVEL RADIOACTIVE WASTE DISPOSAL
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发表时间：
2015
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通讯作者：
Cnnc Key
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作者：
Cnnc Key
在高放废物处置场地的选择和评价中，其水文地质条件是一个重要的因素。透气带的土壤渗透性是水文地质研究的关键问题之一，它影响着土壤表层的入渗、径流和蒸散及其分布关系。对通气区土壤渗透性的分析有助于了解地下水的形成机制。甘肃省的北山是中国高放射性废物处置的一个预选优先区域，而新昌-向阳山是一个预选的优先地点。为此，采用双环法和圭尔夫入渗仪对该预选场地的通气区土壤渗透率进行了调查。采用SPSS 19.0软件，选取土壤有机质、土壤初始含水量、土壤磷含量、土壤容重、土壤总离子含量和土壤粒度分布6个主要影响因子进行主成分分析。本项目旨在获取数据，深入研究该区域土壤水分运动特征和地下水形成循环特征，为预选区域选址和性能评价提供一定的科学依据。结果表明：(1)新昌-向阳三土壤通气区渗透系数的水平分布特征为：1土壤渗透率随位置变化剧烈；2土壤饱和水力传导系数（Kfs）各地貌单元大小依次为沟壑（4×10-5 m s-1）缓坡（1.6×10-5 m s-1）平地（7.69×10-6 m s-1）。因此，可以推断，沟渠是雨水渗入深层土壤形成地下水的主要区域，由于其地下水活跃，应从高废液排土场候选名单中划去；新场断裂带的3 Kfs大于集集草断裂带，平均分别为2.75×10-4 m s-1和9.37×10-5 m s-1。因此，大型断裂带也应从名单中划去，因为它的地下水非常活跃；粘土中的4 Kfs非常低，平均仅为9.99×10-7 m s-1。(2)四十里井盆地4个试验点土壤渗透性在纵向上也存在差异，在深度上Kfs先上升后下降。由于土样数量有限，这种变化的原因和趋势有待进一步探讨。(3)影响Kfs的因素及其机理分析表明，Kfs与土壤理化性质密切相关，主成分分析表明，Kfs的影响因素可归纳为：第一主成分为土壤疏松度，主要受土壤初始含水量、有机质含量和土壤粒度组成的影响；二是基本理化性质，主要包括土壤磷氢含量、土壤总离子含量、土壤容重和土壤粒径（0.5 mm）组成；三是土壤粒度组成，主要是0.1 ~ 0.5 mm大小的颗粒。综上所述，在各影响因子中，中粗砂（0.5 mm）和粘质粉砂（0.1 mm）含量对Kfs的影响最大，中细砂（0.1~0.5 mm）含量最低。
In selecting and evaluating a new dump site for disposal of high-level radioactive waste(HLW)repository,its hydrogeology condition is one of the most important factors. Moreover,soil permeability of the aeration zone is one of the key issues in the study of hydrogeology,affecting water infiltration,runoff and evapotranspiration in the surface soil layer and their distribution relations. Analysis of soil permeability of the aeration zone helps understand the mechanism of groundwater formation. Beishan in Gansu Province is a preselected priority region for disposal of China's HLW,while Xinchang-Xiangyangshan is a preselected priority site. For that end,investigations were carried out on soil permeability of the aeration zone in that preselected site,using the double ring method and and a Guelph infiltration meter in-situ. With the aid of software SPSS 19.0,soil organic matter,initial soil water content,soil p H,soil bulk density,soil total ion content and soil particle size distribution were selected as 6 main affecting factors for principal component analysis. This project was aimed at acquiring data for in-depth study on characteristics of soil water movement and formation and circulation of groundwater in the area,so as to provide some scientific basis for site determination and performance evaluation of the preselected area. The following knowledge and results were obtained:(1)horizontal distribution of permeability coefficients of the soil aeration zone of Xinchang-Xiangyangsan was characterized by 1 soil permeability varied sharply with the location;2 in terms of soil saturated hydraulic conductivity(Kfs),various geomorphic units followed an order of gully(4×10-5 m s-1)slow slope(1.6×10-5 m s-1)flat land(7.69×10-6 m s-1). Therefore,it could be inferred that gullies are the main area where rainwater infiltrates and permeates into deep soil to form groundwater,and an area that should be crossed out from the list of candidates of HLW dump sites,because of its active groundwater;3 Kfs is higher at the Xinchang fault belt than at the Jijicao fault belt,being on average 2.75×10-4 m s-1 and 9.37×10-5 m s-1,respectively. So large-scaled fault belts should also be crossed out from the list due to its highly active groundwater;4 Kfs in clay is very low,being on average only 9.99×10-7 m s-1.(2)Soil permeability also varied vertically,with Kfs rising first and declining later down the soil in depth at the four experimental points in the Sishilijing Basin. As the number of soil samples was limited,causes and trend of the change need to be further explored.(3)Analysis of factors affecting Kfsand its mechanism shows that Kfs is closely related to soil physical and chemical properties,and the principal component analysis indicates that Kfs affecting factors may be summarized as follows:the first principal component may be described as soil looseness,which is affected mainly by initial soil water content,organic matter content and soil particle size composition;the second one is basic physical and chemical properties,mainly including soil p H,soil total ion content,soil bulk density and soil particle size(0.5 mm)composition;and the third one is soil particle size composition,mainly of the particles ranging from 0.1mm to 0.5 mm in size. In a word,among all the affecting factors,the contents of moderate-coarse sands(0.5 mm)and clayey silts(0.1 mm)are the highest in effect affecting Kfs,while the content of medium-fine sands(0.1~0.5 mm)is the lowest.