摘要
华北平原是我国政治、经济、文化和交通中心所在,也是水资源供需矛盾比较严峻的地区。该区主要供水水源是地下水。区内第四系厚度为450-600 m,自上而下分为四个含水层组,Ⅰ含水层组称为浅层咸水,Ⅱ、Ⅲ、Ⅳ含水层组称为深层淡水。深层淡水与浅层咸水构成“上咸下淡”的区域水质结构。长期超量开采深层淡水,深层水由顶托排泄转而变为接受上层水越流补给。浅层水大量混入,并未使深层水矿化度显著提高。有学者进行盐均衡分析表明,浅层咸水在越流过程中被淡化。本文旨在研究咸水渗透实验中的弥散作用,这在深层水资源开发和保护方面有重大的应用价值。通过室内试验和参数计算,研究咸水流过粘性土层时的弥散作用,为进一步研究“咸水淡化”机理打下基础。
关于粘土的滤盐机理,目前有几种说法：Bredehoeft认为,带负电荷的粘土颗粒阻止阴子通过,同时阴离子对阳离子的吸引也阻止了阳离子通过,仅有离子化程度小的水分子可以通过薄膜；Hanshaw等(1973)的解释是,溶液在压力作用下通过粘土层时,粘土孔隙两端会产生电位,流出端为正极,流入端为负极,由于电荷的排斥作用,阳离子不能向流出端运动；另外还有岩土颗粒表面双电层理论等说法。
本项目通过室内咸水渗透实验,研究了咸水在越流过程中与粘土相互作用的机理、过程及影响因素。咸水渗透实验模型与达西渗流实验的基本原理相同。实验所用土样分别取自河北省石家庄、曹妃甸和北京亦庄。土柱实验所用土样均经过烘干、粉碎并过标准筛,粒径<0.1 mm。同时用TST-55型渗透仪对曹妃甸采集的原状土进行渗透试验。同时绘制浓度穿透曲线并计算各土样的弥散参数。
对所得结果进行分析可知,在相同的实验装置下,在本实验尺度下,渗透系数越小,流速越慢的土样,其弥散度越小。而在同样实验条件下,弥散度越小,则土样中截留所流经咸水中盐分的能力越强。
本实验所用土样对水中的盐分的截留作用也解释了前人所研究的现象,即虽然在华北平原区的大尺度上存在浅层咸水向深层淡水的越流,深层淡水的矿化度却并未提高。
The North China Plain is the political, economic, cultural and transportation center of China, and there are severe contradictions between supply and demand of water resources. The main water resources of the North China Plain is groundwater. The thickness of Quaternary system of this area is 450-600 m, containing 4 water-bearing layers:the first one is called shallow(superficial) saline water, and the other three layers are deep fresh water. The fact that saline water is in the superficial and fresh water is deep makes the water quality structure of this area. The deep water no longer discharged to superficial water and turned to accept the recharge from shallow water because of the long-time over pumping. The salinity of deep water did not arised although there entrained a lot of shallow saline water. The equilibrium analysis of salt shows that the shallow saline water turned fresher because of the leakage flow. The aim of this paper is to study on dispersion during saline water flow through clay-bearing soil, which is an important application of the exploitation and protection of deep water resources. Study on dispersion effect by indoor experiment and calculation and lay the foundation to study the mechanism of "the desalting of saline water".
There are several theories about the desalination of soil:Bredehoeft hole the opinion that the soil partical refrained the passage of anion and, at the same time, the cation can not pass since the attraction of anion. As a result of that, only water molecule whose ionization degree is small. Hanshaw, et al. explain the fact in the other way. When solution pass through soil layer with pressure, the side of soil pore will have electric potential. The side flowing out is positive electrode and the side flowing in is negative electrode. Cation can not move to the side flowing out since the exclusion of electron charge. At the same time, there are theories of electric double layer in the surface of soil particles, et al.
This paper study the mechanics, process and influencing factor of the reaction between saline water and soil during the leakage of saline water by indoor experiment. The theory of experimental model is similar to Darcy seepage experiment's. The soil samples and core(原状土)are from Shijiazhuang and Caofeidian in Hebei province and Yizhuang in Beijing. The samples for column experiment is oven-dried, pulverised and sieved which is promised to smaller than 0.1 mm. At the same time, osmotic experiment of soil core from Caofeidian is proceeded by TST-55 osmoscope. Concentration breakthrough curve is drawed and dispersion parameter is calculated.
Analyze the data from different soil samples and experiment equipment could get the conclusion that the soil samples whose hydraulic conductivity is smaller and the flow velocity in it is slower have smaller dispersivity. Under the same experimental condition, the soil samples whose dispersivity is smaller could retain more salt ions from the solution flow through the soil.
The fact that soil samples in these experiments could retain salt ions also explains the phenomenon before that although in the big scale of the North China plain there is leakage flow from the shallow saline water to deep fresh water, the salinity of deep water did not arised.
引文
Matthew W. Becker. Distinguishing Advection, Dispersion, and Diffusiong in Fractured Bedrock. Department of Geology, University at Buffalo, State University of New York, Buffalo,2006
J. D. Bredehoeft, C. R. Blyth, W. A. White, et al. Possible Mechanism For Concentration of Brines In Subsurface Formations. Bulletin of The American Association of Petroleum Geologists,1963,47(2): 257-269
R. O. Van Everdingen. Mobility of main ion species in reverse osmosis and the modification of subsurface brines. Canadian Journal of Earth Science,1968(5):1253-1260
Frederick A. F. Berry. Relative Factors Influencing Membrane Filtration Effects In Geologic Environment. Chemical Geology,1968.
Yousif K. Kharaka and Frederick A. F. Berry. Simultaneous flow of water and solutes through geological membranes-1.Experimental investigation. Geochimica et Cosmochimica Acta,1973(37):2577-2603
Bruce B. Hanshaw and Tyler B. Coplen. Ultrafiltration by a compacted clay membrane-2.Sodium ion exclusion at various ionic strengths. Geochimicaet Cosmochimica Acta,1973(37):2311-2327
Yousif K. Kharaka and Willard C. Smalley. Flow of Water and Solutes through Compacted Clays. The American Association of Petroleum Geologists Bulletin,1976,60(6):973-980.
Takeo Ebina and Rwaichi J.A. Minja. Correlation of hydraulic conductivity of clay-sand compacted specimens with clay properties. Applied Clay Science,2004(26):3-12
Michael A. Malusis, Charles D. Shackelford and Harold W. Olsen. Flow and transport through clay membrane barriers. Engineering Geology 2003(70):235-248
Li Liangxiong, T.M. Whitworth and R. Lee. Construction of an ultrathin, compacted clay membrane for use in reverse osmosis. Applied Clay Science,2003 (24):59-68
Michael A. Malusis and Charles D. Shackelford. Theory for reactive solute transport through clay membrane barriers. Journal of Contaminant Hydrology,2002(59):291-316
Nikolai M. Kocherginsky and Joseph W. Stucki. Supported clay membrane:a new way to characterize water and ion transport in clays. Advances in Environmental Research,2001 (5):197-201
J.D. Sherwood and B. Craster. Transport of Water and Ions Through a Clay Membrane. Journal of Colloid and Interface Science,2000 (230):349-358
N. Foged and J. Baumann. Clay membrane made of natural high plasticity clay:leachate migration due to advection and diffusion. Engineering Geology,1999 (54):129-137
Jacob Bear.《多孔介质流体动力学》.中国建筑工业出版社,1982
张宗祜,沈照理等.华北平原地下水环境演化.北京：地质出版社,2000
宋海波,张兆吉,费宇红等.开采条件下河北平原中部咸淡水界面下移.水文地质工程地质,2007(1)：44-46
郭永海,沈照理,钟佐燊.河北平原咸水下移及其与浅层咸水淡化的关系.水文地质工程地质,1995(2)：8-12
张宗祜,施德鸿,任福弘等.论华北平原第四系地下水系统之演化.中国科学,1997,27(2)：168-173
王兰化.天津市平原区深层淡水咸化-咸水下移问题的讨论.地质调查与研究,2004.09,27(3)：169-176
明木和.衡水深层淡水咸化问题的探讨[J].水文地质二程地质,1986,5.
张宗祜,施德鸿,沈照理等.人类活动影响下华北平原地下水环境的演化与发展.地球学报,1997.11,18(4)：337-344
周炼,刘存富,姜山等.河北沧州地区第四纪地下水~36C1示踪.矿物岩石地球化学通报,2001,20(4)：418-420
牟纯儒,张建平.河北省典型区咸淡水界面下移现状及其入侵机制分析.河北水利水电技术,2002(1)：37-39
王家兵.华北平原深层淡水在开采条件下接受上覆咸水越流补给-以天津平原为例.水文地质工程地质,2002(6)：35-37
王家兵,李平.天津平原地面沉降条件下的深层地下水资源组成.水文地质工程地质,2004(5)：35-37
吴平霄.《粘土矿物材料与环境修复》.化学工业出版社,环境科学与工程出版中心,2004.8
孙讷正.《地下水污染——数学模型和数值方法》.北京：地质出版社,1989
唐大雄,刘佑荣,张文殊等.工程岩土学.北京：地质出版社,1999.8
马建良,陈喜,程勤波等.一维变密度溶质运移实验及参数推求.水资源保护,2008.05(3)：9-11.
中国科学院土壤及水土保持研究所.《华北平原土壤》.科学出版社,1961
中华人民共和国水利部.GB/T 50123-1999.中华人民共和国国家标准-土工试验方法标准.北京：中国计划出版社,1999
陈宗宇.从华北平原地下水系统中古环境信息研究地下水资源演化：[博士学位论文].吉林：吉林大学,2001
王昭.华北平原地下水质量评价及微量有机污染物淋溶迁移性研究：[博士学位论文].中国地质科学院,2008