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Measuring the soil water retention curve (SWRC) using the centrifuge method often results in compressibility and an increase in bulk density. The compressibility and bulk density of the specimen are always assumed to be constant while deducing the SWRC from centrifuge testing, which may cause inaccurate SWRCs. This study proposed an improved genetic algorithm (GA) to inverse the hydraulic parameters and further constructed the SWRC by taking bulk density into account for soils with varying grain size compositions. For this study, sandy loam soils (i.e., seven treatments T1–T7) were prepared based on different volume ratios of coarse (0.075–2 mm) to fine (<0.075 mm) particles. SWRCs including compressibility and bulk density changes were measured using the centrifuge method. For verification, SWRCs were also independently deduced from one‐dimensional infiltration experiments by inverse analysis using the improved GA that combined multi‐objective optimization and elitist strategy. Upon the final shrinkage ratio of 18.32 to ∼26.38%, the bulk density during centrifugation increased by 22.33 to ∼35.72% correspondingly, thereby causing a difference in soil moisture of 9.58 to ∼16.53% between the corrected and uncorrected SWRCs. The comparison between simulated SWRC and two types of measured SWRCs (i.e., corrected and uncorrected SWRC) demonstrated that the corrected SWRC was more reasonable regardless of soil particle compositions. The findings suggest the corrected SWRC considering bulk density changes provides more accurate hydraulic parameters, which can be inversed from the infiltration data using the improved GA.

PurposeTraditional laboratory measurements of soil water diffusivity (D) and soil water retention curve (SWRC) are always time-consuming and labor-intensive. Therefore, this paper aims to present a simple and robust test method for determining D and SWRC without reducing accuracy.Design/methodology/approachIn this study, a D model of unsaturated soil was established based on Gardner–Russo model and then a combination of Gardner–Russo model with one-dimensional horizontal absorption method to obtain n and a parameters of Gardner–Russo model. One-dimensional horizontal absorption experiments on loam, silt loam and sandy clay loam were conducted to obtain the relationships between measured infiltration rate and cumulative infiltration with wetting front distance. Based on the obtained relationships, the measured infiltration data from the one-dimensional horizontal absorption tests were used to calculate n and a parameters and further constructing D and SWRC.FindingsBoth the calculated D and SWRC inversed from the infiltration data were in good agreement with the measured ones that obtained from the traditional horizontal absorption method and the centrifuge method, respectively. Error analysis indicated that only the infiltration data are enough to reliably synchronously determine D and SWRC.Originality/valueA simple and robust method is proposed for synchronous determination of soil water diffusivity and water retention curve.

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