The Estimation of van Genuchten SWCC Model for Unsaturated Sands by means of the Genetic Programming

Abstract

The van Genuchten Model (1980) is widely-used for the description of the Soil-Water Characteristic Curve (SWCC) of a variety of soils. This study uses the Genetic Programming (GP) for the presentation of equations estimating the van Genuchten (vG) Model fitting parameters for unsaturated clean sand soils. Moreover, this study uses the data derived from the valid dataset of Benson et al. (2014), including 95 measured SWCCs in both drying and wetting phases. The data on the particle size distributions includes the fine-grain percentage (Fines %), d60, d10, besides the residual and saturated volumetric water content (θ and θ ), as the GP model inputs of set of terminal. As for the model outputs of set of terminal, the fitting parameters for the vG model include a and n. The functions used in the GP training were 'plus', 'minus', 'times', taken from the MATLAB default functions, 'mydivide' proposed by Silva (2007), and some other new power functions included by this study. Accordingly, new equations were presented for the estimation of vG Model fitting parameters for both forms of wetting and drying. Finally, to evaluate the accuracy of the proposed estimation equations, the GP results were evaluated and verified in different procedures.Keywords: SWCC, van Genuchten Model, Unsaturated Soils, Genetic Programming, Fitting Parameters *Corresponding author. Tel: +98-912-568-3767 Fax: +98-6633243999 E-mail addresses: am.taban@gmail.com (A. Taban); msadeghi@ieht.ac.ir (M. Mirmohammad Sadeghi); mohamali@cc.iut.ac.ir (M.A. Rowshanzamir); Postal Address: Department of Civil Engineering Isfahan (Khorasgan) Branch, Islamic Azad University, Jey Street, Arqavanieh, University Blvd. PO Box: 158-81595, Isfahan, Iran 2 1.IntroductionSoil-Water Characteristic Curve (SWCC) is one of the widely-used concepts in the earth-related sciences, and particularly, in the mechanics of unsaturated soils. It describes the relationship between the amounts of water in the soil structure and the matric suction in the soil. Many analyses and numerical studies of unsaturated soils depend on the SWCC. Such expressions as the volumetric water content, the degree of saturation, and the normalized water content are used for the amount of water within the soil [1].There are various methods for the measurement of SWCC, many of which are costly and time-consuming. However, they are different from each other in terms of their capabilities of measuring different ranges of the suction. What follows is a list of measurement methods that directly measure the SWCC: The Hanging Column, the Pressure Plate Extractor (PPT), the Chilled Mirror Hygrometer, and the Centrifuge, which directly measure SWCC and the procedure has been explained in ASTM D6836 [2]. In contrast, there is another group of experiments which measure the values indirectly, for example: Filter Paper, Heat Dissipation, Thermal Conductivity Sensor Technique, Chilled-Mirror, Hygrometer Technique, and so forth [3]. These methods of suction measurement will measure different ranges of suct...

Estimating the Soil-Water Retention Curve of Arsenic-Contaminated Soil by Fitting Fuentes’ Model and Their Comparison with the Filter Paper Method

“…This resulted in a change in the SWRCs' slope. Such a difference can be explained through the correlation between the value of the parameter 𝑛 and the pore-size distribution because the parameter 𝑛 is a slope function [32,41]. The comparison of the simulated SWRC and the filter paper SWRC is shown in Figure 2 for the three arsenic concentrations with Mualem's restriction.…”

Uncertainty in Determination of the Soil-Water Characteristic Curve Based on the van Genuchten Model

“…Turchenko et al [12] created indium-substituted strontium hexaferrites via the conventional solid-phase reaction and found linear dependence of the unit cell parameters. Tanbn et al [13] proposed formulae estimating the van Genuchten model fitting parameters for unsaturated clean sand soils by using Genetic Programming. Rahimia et al [14] proposed a matrix of unsaturated permeability estimation models including SWCC equations and relative permeability to estimate the unsaturated permeability function.…”

Soil water characteristic curve of a compacted A-7-5 tropical red earth soil

“…Different models have been developed in the field SWCC over the last five decades and some of the notable ones include Brooks and Corey (1964), van Genuchten (1980), Fredlund and Xing (1994), Kosugi (1999), Omuto (2009), Krishnapillai and Ravichandran (2012) [5]. A brief description of the four models used in this study is given in Table 1.…”

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