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67 Hydrology of Swelling Clay Soils

Part 6. Soils

  1. David Smiles1,
  2. Peter A C Raats2

Published Online: 15 APR 2006

DOI: 10.1002/0470848944.hsa071

Encyclopedia of Hydrological Sciences

Encyclopedia of Hydrological Sciences

How to Cite

Smiles, D. and Raats, P. A. C. 2006. Hydrology of Swelling Clay Soils. Encyclopedia of Hydrological Sciences. 6:67.

Author Information

  1. 1

    CSIRO Land and Water, Canberra, Australia

  2. 2

    Wageningen University and Research Centre, Wageningen, The Netherlands

Publication History

  1. Published Online: 15 APR 2006


Theory of water flow in nonswelling soils has been used for more than 50 years but liquid flow in porous media that change volume with liquid content is not well established in soil science, although it is considered increasingly in chemical and mining engineering and in soil mechanics. Theory of water flow in swelling systems must satisfy material continuity; it must also account for changes in the gravitational potential energy of the system during swelling and for anisotropic stresses that constrain the soil laterally but permit vertical movement. A macroscopic, phenomenological analysis based on Darcy's law provides a useful first approach to the hydrology of such soils and, if we presume that volume change, in the large, is essentially one-dimensional, material coordinates based on the vertical distribution of the solid phase result in a water flow equation analogous to the Richards equation for nonswelling soils. This framework fully accounts for the vertical strain of the solid phase, and solutions to the flow equation are available for a wide range of practically important initial and boundary conditions. The approach has been well tested in clay suspensions and in saturated systems such as mine tailings and sediments. It is also applied in soil mechanics and, here, we apply it to swelling soils. As with the use of the Richards equation in rigid soils, we recognize that complications arise, but the approach remains the most coherent and profitable to support current needs and serve as a point of departure for future research. The use of material coordinates is simple. We discuss some experimental difficulties in using the approach and also consider extension of the approach to more than one dimension.


  • clay soils;
  • swelling;
  • water movement;
  • overburden;
  • material coordinates;
  • cracking