Proceedings of the
9th International Symposium for Geotechnical Safety and Risk (ISGSR)
25 – 28 August 2025, Oslo, Norway
Editors: Zhongqiang Liu, Jian Dai and Kate Robinson
Variability Characterization of Model Parameters Of SWCC for Sandy Soils
1Department of Civil Engineering, Birla Institute of Technology and Science (BITS) Pilani Hyderabad Campus, Shamirpet, Hyderabad, Telangana, India
2Department of Civil Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy, Telangana, India.
ABSTRACT
A new statistical framework was employed to quantify the variability in the model parameters of the soil-water characteristic curve (SWCC) for sandy soils. It is essential to have precise estimates of the mean, standard deviation, and probability density function (PDF) of these model parameters in order to ensure a reliability based design in unsaturated soil mechanics. The conventional assumptions of Gaussian or lognormal distributions may not sufficiently capture the significant variability of these model parameters. The objective of this work is to determine the most appropriate continuous probability density functions (PDFs) by optimizing the mean and standard deviation in order to minimize errors in estimating quantiles, percentiles, and cumulative distribution functions (CDFs). Data from 228 sample points, drawn from comprehensive experimental studies on SWCC model parameters for sandy soils, were analyzed. The most appropriate distributions for model parameters of the SWCC vary significantly depending on the type of soil. In Fredlund and Xing's SWCC model, it was determined that the Gamma, Weibull, and Inverse Gaussian distributions are the most suitable for representing the model parameters af(related to air entry value), nf(related to slope of SWCC), and mf(related to residual suction), respectively, in the case of sandy soils. Additionally, the proposed PDFs for sandy soils were considered and applied for aninfinite slope. Analysis of a shallow sandy slope is presented with the appropriate PDFs proposed in this study. The outcomes revealed that the selection of an inappropriate PDF resulted in a significant overestimation of the probability of failure of unsaturated infinite slopes composed of sandy soils. The suggested mean, coefficient of variation (COV), and probability density functions provided by the research are useful for designing and evaluating the performance of unsaturated soil slopes based on reliability.
Keywords: Variability, Probability Density Function (PDF), Unsaturated soils, Soil Water Characteristic Curve (SWCC), Infinite slopes, Reliability analysis.
