Performance Enhancement of the Tuller-Or model for Soil Water Characteristic Curve Via Optimization of The Soil Pore Size Distribution Parameters

Document Type : Research Paper


1 M.Sc. Student, Department of Irrigation and Reclamation Engineering, University of Tehran, Karaj, Iran

2 Department of Irrigation and Reclamation Engineering, University of Tehran, Karaj, Iran

3 Associate Professor, Department of Irrigation and Reclamation Engineering, University of Tehran, Karaj, Iran


Models to explain water characteristic curve and liquid distribution in partially saturated porous media are abundant, mostly based on the “bundle of cylindrical capillaries” (BCC) representation of pore-space geometry. The assumptions in the BCC model are that 1- certain pore sizes are completely filled by liquid whereas larger pores are completely empty at a given saturation level and 2- the surface area and adsorbed liquid films are ignored. Tuller-Or (TO) model is among the few physical-based models that considers both the capillary and adsorption phenomena via introducing a new pore space geometry with angular central pores attached to slit-shape pores. However, the original TO model fails to describe experimental data in the intermediate saturation range because of the limited flexibility of the probability distribution invested for describing the pore size space. In this study a new enhanced form of TO model was proposed which is based on the numerical solution and is capable of using Gamma distribution for pore size distribution with arbitrary shape factor and |Weibull distribution. The results obtained from the optimized model for soils with different textures showed significant improvement compared to the original model, especially in mid-range saturations whereas the original TO model shows low accuracy. The new enhanced version also includes a global search algorithm for fitting the TO model that provides unique set of fitting parameters that are independent of initial guesses.


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