Prediction of the soil-water characteristic curve based on grain-size-distribution and index properties

Y. Y. Perera, Claudia Zapata, W. N. Houston, Sandra Houston

Research output: Chapter in Book/Report/Conference proceedingConference contribution

41 Scopus citations


The grain-size-distribution (GSD) of a soil is intimately related to its pore size distribution and hence, the GSD holds a close relation with the soil-water characteristic curve (SWCC). In addition, the plasticity index (PI) is a measure of the water holding capacity of the soil and therefore, it plays an important role in shaping the SWCC. This paper presents two sets of statistically derived equations that describe the SWCC of non-plastic and plastic soils. Data from 154 non-plastic soils and 63 plastic soils were analyzed. Soil samples were collected as part of the National Cooperative Highway Research Program (NCHRP) 9-23 project entitled Environmental Effects in Pavement Mix and Structural Design Systems. Samples were obtained from underneath paved roads of 30 sites located throughout the United States. The soil samples were subjected to laboratory testing that included index testing and SWCC testing. SWCCs were determined using a newly developed pressure plate device capable of overburden pressure application, continuous measurements of moisture content, and volume change monitoring. In addition to the collected field data, a database of published soil index properties and SWCCs was incorporated to the analysis. Each SWCC data set was fitted with Fredlund and Xing curve, which provided an S-shaped curve with four parameters, a f, b f, C f, and h rf. Using multiple regression analysis, equations were derived for these four parameters based on predictors derived from GSD and PI. The equations presented in this paper are useful in predicting the SWCC of any given soil without carrying out actual SWCC testing and they can easily be incorporated into computer codes to solve various unsaturated soil mechanics problems such as determining moisture beneath covered areas.

Original languageEnglish (US)
Title of host publicationGeotechnical Special Publication
Number of pages12
StatePublished - 2005
EventGeo-Frontiers 2005 - Austin, TX, United States
Duration: Jan 24 2005Jan 26 2005


OtherGeo-Frontiers 2005
Country/TerritoryUnited States
CityAustin, TX

ASJC Scopus subject areas

  • Building and Construction
  • Architecture
  • Soil Science


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