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Experimental and Mathematical Investigation of Time-Dependence of Contaminant Dispersivity in Soil

机译：土壤中污染物弥散度随时间变化的实验和数学研究

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Laboratory and field experiments have shown that dispersivity is one of the key parameters in contaminant transport in porous media and varies with elapsed time. This time-dependence can be shown using a time-variable dispersivity function. The advantage of this function as opposed to constant dispersivity is that it has at least two coefficients that increase the accuracy of the dispersivity prediction. In this study, longitudinal dispersivity values were obtained for the conservative NaCl solute transport in a laboratory porous medium saturated with tap water. The results showed that the longitudinal dispersivity initially increased with time (pre-asymptotic stage) and eventually reached a constant value (asymptotic stage). Four functions were used to investigate the time variations of dispersivity: linear, power, exponential and logarithmic. In general, because of the linear increase of dispersivity during a long time of transport, the linear function with R2=0.97 showed better time variations than the other three functions; the logarithmic function, having an asymptotic nature, predicted the asymptotic stage successfully (R2=0.95). The ratio of the longitudinal dispersivity to the medium length was not constant during the transport process and varied from 0.01 to 0.05 cm with elapsed time.
机译：实验室和现场实验表明，分散性是污染物在多孔介质中传输的关键参数之一，并且会随着时间的流逝而变化。可以使用随时间变化的色散函数来显示这种时间依赖性。与恒定分散度相反，此功能的优点是它具有至少两个系数，这些系数增加了分散度预测的准确性。在这项研究中，获得了在自来水饱和的实验室多孔介质中保守的NaCl溶质迁移的纵向分散性值。结果表明，纵向弥散度最初随时间增加（渐近前阶段），最终达到恒定值（渐近阶段）。四个函数用于研究分散性的时间变化：线性，幂，指数和对数。通常，由于在长时间的运输过程中分散度的线性增加，R2 = 0.97的线性函数显示出比其他三个函数更好的时间变化。具有渐近性质的对数函数成功地预测了渐近阶段（R2 = 0.95）。在运输过程中，纵向分散度与介质长度的比值不是恒定的，并且随着时间的流逝在0.01到0.05 cm之间变化。

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