Abstract: The water flow in unsaturated soil is controlled mainly by the soil-water characteristic curve (SWCC) and the coefficient of permeability of the soil, both of which are functions of the soil suction. Experimental measurement of both the SWCC and permeability function is time consuming and costly. As a result, indirect methods for estimating the permeability function from the SWCC are commonly accepted by researchers. Among different indirect methods for the estimation, statistical methods have been proven to be rigorous and reliable. They provide discrete results for the permeability function corresponding to different soil suctions, and the estimations are dependent on the division of SWCC segments. In this paper, we adopt two approaches with different procedures to estimate the permeability function using statistical methods. The first approach evenly divides the SWCC in the domain of volumetric water content, and the second evenly divides the SWCC in the domain of matric suction. The effects of the SWCC segments on the permeability function estimated from the SWCC (including unimodal and bimodal curves) using both approaches are investigated and discussed. A minimum number of 40 segments is recommended for the estimation. We recommend that the SWCC should be divided within the matric suction domain rather than the volumetric water content domain for the estimation of the permeability function using statistical methods.

Key words: Permeability function; Statistical methods; Estimation; Soil-water characteristic curve

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