Improved evaporation method for the measurement of the hydraulic conductivity of unsaturated soil in the wet range
Improved evaporation method for the measurement of the hydraulic conductivity of unsaturated soil in the wet range
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DOI：
10.1016/j.jhydrol.2018.06.005
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发表时间：
2018-08
影响因子：
6.4
通讯作者：
N. Masaoka;K. Kosugi
中科院分区：
文献类型：
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作者：
N. Masaoka;K. Kosugi
蒸发法是测量土壤水力特性的一种有效方法。然而，当土样内部的水力梯度超过压力传感器的最小精度时，EM通常无法测量湿（低吸力）范围内的水力导率曲线（K - h， K和h分别为水力导率和压头）。在这项研究中，我们开发了一种新的实验装置，使用EM在湿范围内进行电导率测量。通过两项重大改进，我们成功地将K-h的可测量范围扩展到湿范围，从而实现准确有效的测量。首先，利用差压传感器显著提高了水力梯度测量的精度。假设最小蒸发速度（土壤样品中心0.18 cm/d），对任何类型的土壤，K-h的可测范围可达27 cm/d。也就是说，我们的装置在湿端将EM可测量的K-h范围扩大了两个多数量级。其次，我们的装置可以在同一样品上执行饱和/非饱和稳态渗透法（SSIM/USIM）和EM。这不仅减少了时间和成本，而且减少了不同方法之间的误差，确保了良好的准确性和代表性。USIM可测量的K-h范围大于21 cm/day，与EM可测量的范围重叠。因此，我们的设备可以获得任何类型土壤从饱和到中压范围（- 500< h≤0 cm）的连续K-h曲线。
The evaporation method (EM) is an effective technique for measuring soil hydraulic properties. However, the EM generally fails to measure hydraulic conductivity curves (K–h; K and h are the hydraulic conductivity and the pressure head, respectively) in the wet (low suction) range when the hydraulic gradient within soil samples exceeds the minimum accuracy of the pressure transducer. In this study, we developed a new experimental device that uses the EM to perform conductivity measurements in the wet range. By making two major improvements, we successfully expanded the measurable range of K–h to cover the wet range, enabling accurate and effective measurements. Firstly, the accuracy of the hydraulic gradient measurement was remarkably improved by the use of a differential pressure transducer. Assuming the minimum evaporation speed (0.18 cm/day at the center of soil sample), the estimated measurable range of K–h is up to 27 cm/day for any type of soil. That is, our device has expanded the range of K–h measurable by the EM by more than two orders of magnitude on the wet end. Secondly, our device can execute the saturated/unsaturated steady-state infiltration method (SSIM/USIM) and the EM on the same sample. This diminishes not only time and cost but also errors between different methods, ensuring good accuracy and representativeness. The range of K–h measurable by the USIM was determined to be more than 21 cm/day, which overlaps with the range measurable by the EM. As a result, our device can obtain consecutive K–h curves from saturation to the medium pressure range (− 500< h⩽ 0 cm) for any type of soil.