The Development of Soil Water Characteristic Curves for Soils Types Classified According to the USCS

Mine waste geotechnics, geochemistry and biology


Ken Mercer


University of Western Australia

The soil-water characteristic curve (SWCC) is one of the most essential soil properties in unsaturated soil mechanics. The water flow and storage characteristics of an unsaturated soil are closely related to the amount of water contained in the pores and the negative pore-water pressure in the soil. These are both in turn, related to the particle-size distribution and the plasticity of the soil.

The SWCC can be used to derive the permeability function of soil, and it is used for characterizing the flow of water in unsaturated embankments and the stability of slopes due to rainwater infiltration into slopes. The SWCC is obtained by laboratory testing which is difficult to perform, costly and time consuming. The advantage of establishing typical SWCC envelopes for different soil types is therefore apparent from a geotechnical design and analysis viewpoint.

This paper presents the research work undertaken by UWA and NTU to develop SWCC envelopes for soil types classified in terms of the ASTM D2487 unified soil classification system.

This was done by establishing a large database of soils from across the world, classifying them according to ASTM D2487 and undertaking SWCC testing for each soil. The paper presents the SWCC test results from a selection of the most common soil classifications encountered in geotechnical engineering practise. For each soil classification selected, the paper will present:

  1. the laboratory tested and curve fitted particle-size distribution (PSD)
  2. the SWCC drying curves showing lab data and best fitting equations for upper, lower and mean.

These results will form a guideline for geotechnical engineers in the field of unsaturated soil analysis.

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