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Critical state soil mechanics

During your undergraduate courses you have already touched upon many different aspects of soil mechanics such as the particulate nature of soils (clay, silt, sand), compressibility (volume change upon loading) and shear strength. However, so far these were considered as independent phenomena. Critical State Soil Mechanics (CSSM) introduced by Roscoe, Schofield and Wroth in 19591 provides a simple framework that links the concept of compressibility to the dependency of shear strength on the stress state and by that improves our understanding of soil behaviour. A detailed introduction into CSSM is given in2, which can be freely accessed.

In last decades there has been a debate on if3 or if not4 to include CSSM into undergraduate courses as it might be too complicated and potentially not very useful for natural soils, especially clays4. Without any doubts, as with all models, not all aspects of soil behaviour can be explained or accurately described by the critical state concept due to its simplicity. However, although its simplicity CSSM allows for the first time to link so far considered unrelated aspects of soil behaviour and by doing so - in my opinion - strengthening and improving our understanding of soil behaviour. Important attributes of natural soils, such as anisotropy, the impact of microstructure, viscosity, and partial saturation, which aren't directly covered by the classical CSSM, can be viewed as enhancements or extensions of it, as highlighted in5. Given the increasing reliance on and demand for advanced numerical strategies in geotechnical design, especially where traditional methods are inadequate, the prominence of CSSM is likely to surge. As such, those well-versed in its foundational principles will be ahead of the curve in addressing future challenges.

In many textbooks, critical state soil mechanics (CSSM) is introduced using results from laboratory experiments on clay. However, in this course, we will approach CSSM by progressively examining the results from an extensive laboratory campaign on sand, led by Prof. Torsten Wichtmann6. This section lays the foundation for the forthcoming topic on soil behaviour under cyclic and dynamic loading.

  1. K. H. Roscoe, A. N. Schofield, and C. P. Wroth, ‘On The Yielding of Soils’, Géotechnique, vol. 8, no. 1, pp. 22–53, Mar. 1958, doi: 10.1680/geot.1958.8.1.22. ↩

  2. A. N. Schofield and P. Wroth, Critical state soil mechanics. in European civil engineering series. London, New York [etc.]: McGraw-Hill, 1968. ↩

  3. D. Airey and G. Miao, ‘Why Critical State Soil Mechanics should be taught to all civil engineers’, 2016. ↩

  4. L. Wesley, ‘(What) To teach or not to teach – from theory to practice’, Geotechnical Research, vol. 2, no. 4, pp. 139–147, Dec. 2015, doi: 10.1680/jgere.15.00005. ↩↩

  5. S. Leroueil and D. Hight, ‘Behavior and properties of natural soils and soft rocks’, in Characterisation and engineering properties of natural soils, vol. 1, Swets \& Zeitlinger, Lisse, The Netherlands, 2003, pp. 29–254. ↩

  6. T. Wichtmann and T. Triantafyllidis, ‘An experimental database for the development, calibration and verification of constitutive models for sand with focus to cyclic loading: part I—tests with monotonic loading and stress cycles’, Acta Geotech., vol. 11, no. 4, pp. 739–761, Aug. 2016, doi: 10.1007/s11440-015-0402-z. ↩