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Soil shrinkage property during soil water characteristic curves being measured by centrifuge method |
NIE Kunkun1, NIE Weibo1*, MA Xiaoyi2 |
1. Institute of Water Resources, Xi′an University of Technology, Xi′an, Shaanxi 710048, China; 2. College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China |
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Abstract Soil water characteristic curves(SWCC)were measured by employing centrifugal method based on the sandy and clay loams in Yangling District of Shaanxi Province in this study. The aim is to study soil shrinking property during the measurement. Three initial bulk densities were set up for the two kinds of soils, and soil shrinking characteristics were clarified in terms of soil hydraulic parameters measured. The test data were best fitted by making used of van Genuchten-Mualem(VG-M)model in two scenarios, i.e. bulk density variation is considered or not, to obtain SWCCs. Two-dimensional numerical simulations were performed to obtain water transport features under furrow irrigation based on the soil hydraulic parameters determined, and the rationality of these parameters was argued according to the indoor experiments conducted. The results show that soil moisture content decreases, but soil bulk density increases gradually with increasing centrifuge speed(soil water suction). As the soil water suction is 7 000 cm, the soil bulk densities of the sandy and clay loams are 1.81 and 1.79 g/cm3, respectively. Based on the soil shrinking characteristics curve, the shrinking process of the sampled soils can be represented by a three-piecewise linear model for different ranges of soil water suction. The residual soil moisture θr and parameter a are larger, but the shape factor n is smaller in the VG-M model when the bulk density variation is considered in comparison with those obtained without variation in the bulk density. The parameters obtained by considering the variation in bulk density were input into software HYDRUS to simulate a two-dimensional furrow irrigation. The simulated results indicated that the averaged errors in the cumulative infiltration and the displacements of wetting front in the horizontal and vertical directions were 5.8%, 3.0%, and 2.6%, respectively, compared with the experimental data. Meanwhile, the accuracy of predictions of the cumulative infiltration and wetting front displacements in terms of the parameters determined by considering the variation in bulk density is better by 39.2%, 57.2%, and 52.9%, respectively, than that without variation in the bulk density. Therefore, the variation of soil bulk density should be considered when a SWCC is measured by using centrifugal method. As a result, the soil hydraulic parameters estimated in this way can significantly improve the accuracy of soil water transport process simulation.
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Received: 30 October 2017
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