Estimating Relative Hydraulic Conductivity from the Water Release Characteristic of a Shrinking Clay Soil
Estimating Relative Hydraulic Conductivity from the Water Release Characteristic of a Shrinking Clay Soil
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DOI：
10.2136/sssaj2009.0356
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发表时间：
2010-07
影响因子：
2.9
通讯作者：
A. Gregory;N. Bird;W. R. Whalley;G. Matthews
中科院分区：
文献类型：
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作者：
A. Gregory;N. Bird;W. R. Whalley;G. Matthews
为了了解土壤的水力特性，需要对非饱和导电性进行准确的预测，而非饱和导电性通常来源于土壤水分释放特性。在细质土壤中，修正的Mualem-van Genuchten （MMVG）函数已被广泛用于预测相对电导率随基质电位变化的变化，但这假设土壤是刚性的，具有恒定孔隙率（CP），这对于收缩土壤是不现实的。我们使用三轴细胞装置来精确监测粘土中水分释放过程中土壤体积的变化。由此，我们得到了基于MMVG （CP）或基于几何相似收缩率（GSS）的相对水力导率函数，该函数由测量的收缩孔隙率（SP）计算得出。MMVG （CP）函数预测，从0到-400 kPa的基质电位范围内，相对电导率将下降3个数量级。这与已发表的关于同一土壤中电导率对较大孔隙固结的响应的数据相似。然而，基于SP，由于正常收缩，土壤保持有效张力饱和（>0.97）至-85 kPa的基质势。相应的GSS （SP）函数预测在此范围内相对电导率仅从1到0.85适度下降。在这种情况下，较大的孔隙虽然尺寸减小，但被假定为仍然充满水并具有导电性。GSS函数可能是张力饱和收缩粘土中水力功能最真实的写照。
To understand the hydraulic properties of soils, accurate prediction of the unsaturated hydraulic conductivity is needed, which is commonly derived from the soil water release characteristic. In fine-textured soils, the modified Mualem-van Genuchten (MMVG) function has been used extensively to predict the change in relative conductivity with changes in matric potential, but this assumes that the soil is rigid with a constant porosity (CP), which is unrealistic for shrinking soils. We used a triaxial cell apparatus to accurately monitor soil volume changes during water release in a clay soil. From this we derived relative hydraulic conductivity functions based on either MMVG (CP), or based on geometrically similar shrinkage (GSS) of all pore sizes by a constant factor as calculated from the measured shrinking porosity (SP). The MMVG (CP) function predicted a decline in relative conductivity of up to three orders of magnitude from 0 to -400 kPa matric potential. This was similar to published data on the response of conductivity in the same soil to consolidation of larger pores. Based on SP, however, the soil remained effectively tension saturated (>0.97) down to a matric potential of -85 kPa due to normal shrinkage. The corresponding GSS (SP) function predicted only a modest decrease in relative conductivity from 1 to 0.85 across this range. In this case the larger pores, although reduced in size, are assumed to be still water filled and conducting. The GSS function was probably the most realistic portrayal of hydraulic functioning in a tension-saturated shrinking clay soil.