Prediction and modeling of tensile stresses and shrinkage
Volume change as a result of drying is often neglected in soil mechanics and soil hydrology, despite the important influence it has in the change of mechanical stability and water flow. Therefore, processes which lead to volume change have to be understood. Tensile stresses as the main parameter for shrinkage are a result of hydraulic and mechanical mechanisms in unsaturated soils or soil substrates. Both mechanisms have to be recognised as dependent processes. Unsaturated soils are defined as 3-phase systems. Capillary forces in soil pores act as contractive forces of the liquid phase on the solid phase. The resulting tensile stress caused by water increases with decreasing degree of water saturation. This causes shrinkage in a given soil volume, including soils with small plasticity. Mechanical stress parameters will simultaneously be changed with shrinkage, which as a result also change the hydrological parameters altering the pore system. The separation of the mechanical from the hydraulic stressis difficult. Therefore, a method was developed, which allows the determination of tensile stress under defined boundary conditions and is based on the general stress equation. Also a method is described by which this information is used for general modeling of volume change by hydraulic stress and general empirical functions used in hydraulic modeling.
KeywordsTensile Stress Void Ratio Unsaturated Soil Water Retention Curve Moisture Ratio
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- Baumgartl, T. and Horn, R. 1999. Influence of mechanical and hydraulic stresses on hydraulic properties of swelling soils. In: M.T. van Genuchten and F.J. Leij (Editors), Characterization and measurement of the hydraulic properties of unsaturated porous media. University of California, Riverside, California pp. 449–458.Google Scholar
- Baumgartl, T., Rostek, J. and Horn, R. 2000. Internal and external stresses affecting the wat er retention curve. In: R. Horn, J.J.H. van den Akker and J. Arvidsson (Editors), Subsoil compaction. Distribution, Processes, consequences. Advances in Geoecology. Cat ena Verlag, Reiskirchen, pp. 3–12.Google Scholar
- Bishop, A.W. 1961. The measurement of pore pressure in the triaxial test. Pore pressure and suction in soils. Butterworths, London, pp. 38–46.Google Scholar
- Fredlund, D.G. and Rahardjo, H. 1993. Soil mechanics for unsaturated soils. A. Wiley, New YorkGoogle Scholar
- Groenevelt, P.H., and G.H. Bolt. 1972. Water retention in soils. Soil Sci. 113: 238–245.Google Scholar
- Low, P.F. 1958. Movement and equilibrium of water in soil systems as affected by soil water forces. High Res. Bd. Spec. Rept., No. 40.: 55–63.Google Scholar
- Matyas, E.L. and Radhakrishna, H.S. 1968. Volume change characteristics of partially satu rated soils. Geotechnique, 18: 432–448.Google Scholar
- Richards, B.G. 1966. The significance of moisture flow and equilibria in unsaturated soils in relation to the design of engineering structures built on shallow foundations in Australia, Symp. on Permeability and Capillary. Amer. Soc. Testing Materials, Atlantic City, NJ.Google Scholar
- Simunek, J., van Genuchten, M.T. and Sejna, M., 1998. Code for simulating the one dimensional movement of water, heat and multiple solutes in variably saturated porous media. US Salinity Laboratory, USDA, ARS, Riverside, CA, USA.Google Scholar
- Toll, D. G. (1995): A conceptual model for the drying and wetting of soil. E. E. Alonso and P. Delage: First International Conference on unsaturated soil. Balkema, Rotterdam, Paris/France, 805–810.Google Scholar
- van Genuchten, M.T. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J., 44: 892–898.Google Scholar
- Waldron, L.J., McMurdie, J.L. and Vomocil, J.A. 1961. Water retention by capillary forces in an ideal soil. Soil Sci. Soc. Am. Proc., 25: 265–267.Google Scholar