Prediction of unsaturated permeability curve of compaction loess with pore-size distribution curve and its application scope

The unsaturated permeability curve is governed by the pore-size distribution curve, which can be used to predict the permeability curve. In order to investigate the applicability of this method for compacted loess, three groups of compacted loess samples with different dry densities were prepared. The pore-size distribution (PSD) curves of soil samples were measured using mercury injection porosimeter test. The unsaturated permeability curves of soil samples were measured by small soil column equipment designed by our research group. Then the PSD curves were used to predict the permeability curves and compared with the measured data from soil column test. The results show that the permeability curves of compacted loess can be divided into a low matric suction stage dominated by capillary water, and a high matric suction stage dominated by adsorbed water. In the low suction stage, the permeability curves of the three soil samples differ greatly. While in the high suction section, the permeability curves of the three soil samples coincide, indicating that the permeability of the high suction section has nothing to do with the density of soil. In addition, the predicted results of three groups of soil samples are in good agreement with the measured data in the low suction section, but the predicted results in the high suction section are smaller than the measured results. It can be seen from the principle of the prediction method that this method is suitable for capillary water but not for adsorbed water. Therefore, a modified method is proposed for the prediction of permeability curve in the high suction section, and the modified method can describe the permeability curve in the whole matric suction range.