Establishment of the relationship between soil suction and water content, commonly termed as soil–water characteristic curve (SWCC), is of prime importance in the field of unsaturated soil mechanics. There are several instruments available that can be used to measure the SWCC of soil, but every suction measuring device has its own limitations in terms of its suction measurement range. Therefore, the preciseness of the estimated unsaturated soil properties largely depends on the range of suction measurements and the type of instruments used. The primary objective of this study is to quantify the error that can occur during the estimation of unsaturated hydraulic conductivity function (UHCF) from SWCC for low plastic soils. Experiments were performed to investigate the influence of different suction measurement devices on the estimated UHCF for four different soils with varying clay content. A dew point potentiometer (WP4) and a miniature tensiometer (T5) have been used in this study for the suction measurement. The SWCC of the selected soils were predicted mathematically using a commonly used pedo-transfer function (PTF). The experimental results clearly indicated that the sole use of WP4 overestimated the SWCC parameters, as well as UHCF (overestimation in the conductivity value is in order of 10⁴ times). Rather, a combination of T5 and WP4 data, within their accurate range, provides a more precise estimation of UHCF. Further, the accuracy of the PTF was found very effective for low plastic soils with a relatively low percentage of clay (% clay < 10), in the absence of any experimental data.

在非饱和土壤力学领域中，建立土壤吸力与含水量之间的关系（通常称为土壤水特征曲线（SWCC））至关重要。有几种可用于测量土壤SWCC的仪器，但是每种吸力测量设备在吸力测量范围方面都有其自身的局限性。因此，估计的非饱和土壤特性的精确度在很大程度上取决于吸力测量的范围和所用仪器的类型。这项研究的主要目的是量化在用SWCC估算低塑性土壤的非饱和导水率函数（UHCF）时可能发生的误差。进行了实验，研究了四种不同粘土含量不同的土壤，不同的吸力测量设备对估计的UHCF的影响。这项研究使用露点电位计（WP4）和微型张力计（T5）进行吸力测量。使用常用的pedo-transfer函数（PTF）对选定土壤的SWCC进行数学预测。实验结果清楚地表明，仅使用WP4会高估SWCC参数以及UHCF（电导率值的高估约为10 使用常用的pedo-transfer函数（PTF）对选定土壤的SWCC进行数学预测。实验结果清楚地表明，仅使用WP4会高估SWCC参数以及UHCF（电导率值的高估约为10 使用常用的pedo-transfer函数（PTF）对选定土壤的SWCC进行数学预测。实验结果清楚地表明，仅使用WP4会高估SWCC参数以及UHCF（电导率值的高估约为10⁴次）。相反，将T5和WP4数据组合在一起，可以在其准确范围内提供对UHCF的更精确估算。此外，在没有任何实验数据的情况下，发现PTF的精度对于粘土含量相对较低（％粘土<10）的低塑性土壤非常有效。