Statistical Assessment of Hydraulic Properties of Unsaturated Soils

G.F.N. Gitirana Jr., D.G. Fredlund


Soils and Rocks, São Paulo, 39(1): 81-95, January-April, 2016 | PDF


The availability of statistical values for soil parameters is essential in reliability-based geotechnical design and sensitivity analysis. Unfortunately, there are few statistical studies available about unsaturated soil parameters. The primary objective of this paper is to present a methodology for the statistical assessment of hydraulic properties of unsaturated soil and to present the results of a statistical study carried out using a large database of soil properties. Two fundamental unsaturated soil properties are considered; namely, the soil-water characteristic curve (SWCC) and the hydraulic conductivity function. Appropriate nonlinear functions and fitting parameters with well-defined and unique physical and/or geometrical meanings were adopted. The main contribution of this article is the establishment of central tendency measures, standard deviations, and correlation coefficients for the unsaturated soil parameters, considering soil datasets grouped according to soil texture. It was determined based on the analyses results that the air-entry value, primary SWCC slope, residual SWCC slope, saturated hydraulic conductivity, and hydraulic conductivity function slope could be well described using lognormal probability density functions. Finally, general guidelines are provided regarding the statistical values to be adopted for the unsaturated soil properties studied.

Invited Article, no discussion.