An experimental and modeling study of water infiltration on water-repellent soil

This study explores the infiltration law for water-repellent soil and identifies the most suitable mathematical model. A laboratory experiment was conducted using a one-dimensional vertical soil column, and the water infiltration into this column was measured for both hydrophilic and hydrophobic soils from the Guishui River basin. The experimental data were then fitted using a Kostiakov piecewise function, Fourier series, first-order Gaussian function, and Gaussian piecewise function. The results indicate that the cumulative infiltration increases to a plateau, whereas, for hydrophobic soil, the infiltration rate is a single-peak curve that increases and then decreases with time. Model graphical analysis shows that the Kostiakov piecewise function model has a maximum and a minimum value appear simultaneously at inflection point of infiltration rate. The produces multiple peaks that do not reflect the monotone increase and decrease of the infiltration rate either side of the peak for Fourier series model. The first-order Gaussian function model cannot replicate the test phenomenon whereby the infiltration rate after the maximum is greater than before. If we ignore the rapid infiltration process at the beginning of the experiment, the Gaussian piecewise function model not only reflects the monotone increase and decrease either side of the peak infiltration rate, but also produces the experimental phenomenon whereby the infiltration rate after the maximum is greater than before.