松散岩类孔隙介质水动力弥散规律及其空间尺度效应研究

发布时间：2018-03-11 20:13

本文选题：水动力弥散　切入点：空间尺度效应　出处：《西南交通大学》2015年硕士论文　论文类型：学位论文

【摘要】：水动力弥散系数为表征污染物在含水层中迁移、分布的重要参数。国内外大量研究发现,该参数随研究时间、空间范围变化而具有尺度效应。如果能够准确把握第四系松散岩类孔隙含水介质水动力弥散规律及其空间尺度效应变化规律,无疑将有助于为该类含水介质地下水的溶质运移数值模拟和污染防治提供基本参数和理论依据。本文在总结国内外文献的基础上,分别采用室内模拟试验、现场弥散试验及数值模拟方法,对松散岩类孔隙含水介质水动力弥散规律及其尺度效应进行了研究。(1)室内弥散试验结果表明：①渗透性较好的松散沉积物中,溶质浓度不是弥散系数确定的主要控制因素,当溶质由510mg/L增至2040mg/L时,弥散系数仅增加1.1-15.7%。②调整孔隙介质骨架构成,试验柱体弥散度随砂柱中粘土混合比例增加而降低,粒径为0.25～0.5mm砂弥散度为4.48cm,随混入粒径5～50μm粘土体积比由1/9增至1/5,介质平均弥散度降至2.97～1.845cm。③确定的孔隙含水介质中,渗流速度为水动力弥散系数的主要影响因素,调整弥散柱体渗流速度由0.026cm/min增至0.051cm/min,弥散系数增大了2.29～2.32倍。④弥散空间尺度效应仅存在于非均质孔隙介质较远距离运移过程中,实验室采用粒度分布较均匀孔隙介质进行的短距离弥散试验,实质为模拟均匀介质的水动力弥散过程,不会出现弥散空间尺度效应。平均粒径0.25～0.5mm砂及砂混粘土(平均粒径5-50pmm)在运移距离为0.8～1.2m时进行水动力弥散试验,弥散度随示踪剂迁移距离增加基本保持稳定。(2)现场弥散试验结果显示,示踪剂投加孔下游1m、10m和40m运移范围确定的纵向水动力弥散度分别为0.069m、0.519m和0.969m。随溶质运移距离增加10～40倍,弥散度增大7.5～14倍,研究区水动力弥散空间尺度效应明显。(3)结合现场弥散系数随运移距离变化特点,根据分维度公式确定研究区弥散度αL与运移距离L满足函数关系αL=10-1.122·L0.733。根据该函数关系,可估算研究区不同运移距离弥散度,为同类型含水介质溶质运移模拟参数选取提供依据。(4)根据现场水文地质条件,采用Modflow软件建立数值模型对现场弥散试验进行模拟,结果表明：受弥散空间尺度效应影响,以现场lm及40m溶质运移距离确定的弥散度作为模型参数均无法较好的模拟示踪剂投放孔下游40m位置浓度随时间变化的实测情况。采用研究区弥散度分维度公式求取40m运移距离算术平均弥散度α,以α作为模型弥散度进行溶质运移模拟,模拟结果可较客观地反映溶质运移起始点下游40m位置浓度随时间变化。由此可见,在该类含水介质中进行地下水污染数值模拟时,以前述函数关系先估研究范围内算术平均弥散度α,进而以α作为模型参数,可提高模拟结果的准确性。
[Abstract]:The hydrodynamic dispersion coefficient is an important parameter to characterize the transport and distribution of pollutants in the aquifer. If we can accurately grasp the hydrodynamic dispersion law of porous water-bearing medium of Quaternary loose rock and the variation law of spatial scale effect, It will undoubtedly be helpful to provide basic parameters and theoretical basis for numerical simulation of solute transport and pollution prevention and control of groundwater in this kind of water-bearing medium. In situ dispersion test and numerical simulation method, the hydrodynamic dispersion law and its scale effect in porous porous media of loose rock are studied. The solute concentration is not the main controlling factor for determining the dispersion coefficient. When the solute concentration increases from 510mg / L to 2040mg / L, the dispersion coefficient increases only by 1.1-15.7.2, and the dispersion degree of the test column decreases with the increase of clay mixing ratio in the sand column. The particle size is 0.25 ~ 0.5mm and the dispersion of sand is 4.48 cm. With the increase of clay volume ratio of 5 ~ 50 渭 m from 1/9 to 1 / 5, the average dispersion of the medium decreases to 2.97 ~ 1.845 cm ~ (3), and the seepage velocity is the main factor influencing the hydrodynamic dispersion coefficient. When the flow velocity of dispersion cylinder is increased from 0.026 cm / min to 0.051 cm / min, the dispersion coefficient increases by 2.29 ~ 2.32 times, and the dispersion spatial scale effect only exists in the long distance migration of heterogeneous porous media. In the laboratory, the short distance dispersion test carried out by a porous medium with a more uniform particle size distribution is essentially a simulation of the hydrodynamic dispersion process of the homogeneous medium. There will be no dispersion spatial scale effect. The hydrodynamic dispersion test is carried out when the migration distance is 0.8 ~ 1.2m, and the mean diameter is 0.25 ~ 0.5 mm sand and sand mixed clay (mean diameter 5-50 pmm). The results of field dispersion test show that the longitudinal hydrodynamic dispersion is 0.069 m / 0. 519 m and 0. 969m, respectively, and increases by 1040 times with solute transport distance, the results of field dispersion test show that the range of migration of tracer is 0. 069 m ~ 0. 519 m and 0. 969m respectively, and the range of migration of tracer is 1 m ~ 10 m and 40 m downstream of the hole, respectively, and the dispersion degree is 0. 069 m ~ 0. 19 m and 0. 96 9 m. The dispersion degree increases by 7.5 ~ 14 times, and the spatial scale effect of hydrodynamic dispersion is obvious. According to the dimensionality formula, the functional relationship between dispersion degree 伪 L and transport distance L is determined. According to the function relationship, the dispersion degree of different transport distances in the study area can be estimated. This paper provides a basis for selecting the parameters of solute transport simulation in the same type of water-bearing medium. According to the hydrogeological conditions in the field, the numerical model is established by using Modflow software to simulate the field dispersion test. The results show that it is affected by the spatial scale effect of dispersion. Based on the dispersion of solute transport distance of lm and 40m in the field, it is impossible to simulate the variation of the concentration of 40 m downstream of the tracer hole with time. The dispersion dimension formula of the study area is used to solve the problem. Taking the 40m migration distance as the arithmetic mean diffusivity 伪, the solute transport simulation is carried out with 伪 as the model dispersion degree. The simulation results can objectively reflect the variation of concentration at 40m downstream of the starting point of solute migration with time. It can be seen that the numerical simulation of groundwater pollution in this kind of water-bearing medium is carried out. The accuracy of the simulation results can be improved by first estimating the arithmetic average dispersion 伪 in the scope of the study and then using 伪 as the model parameter.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X523

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