A bounding surface plasticity model for unsaturated soil at small strains

C. Zhou, Charles Wang Wai Ng, R. Chen

Research output: Journal article publicationJournal articleAcademic researchpeer-review

30 Citations (Scopus)


Most existing hydromechanical models for unsaturated soils are not able to fully capture the nonlinearity of stress-strain curves at small strains (less than 1%). They cannot therefore, for example, accurately predict ground movements and the performance of many earth structures under working conditions. To tackle this problem, a state-dependent bounding surface plasticity model has been newly developed. Particularly, the degradation of shear modulus with strain at small strains ranging from 0.001% to 1% is focused. The proposed model is formulated in terms of mean average skeleton stress, deviator stress, suction, specific volume and degree of saturation. Void ratio-dependent hydraulic hysteresis is coupled with the stress-strain behaviour. Different from other elastoplastic models for unsaturated soils, plastic strains are allowed inside bounding surfaces. In this paper, details of model formulations and calibration procedures of model parameters are presented. To evaluate the capability of the new model, it is applied to simulate a series of triaxial compression tests on compacted unsaturated silt at various suctions. Effects of suction, drying and wetting as well as net stress on unsaturated soil behaviour are well captured. The model shows good predictions of the degradation of shear modulus with strain over a wide range of strains from 0.001% to 1%.

Original languageEnglish
Pages (from-to)1141-1164
Number of pages24
JournalInternational Journal for Numerical and Analytical Methods in Geomechanics
Issue number11
Publication statusPublished - 10 Aug 2015
Externally publishedYes


  • Constitutive model
  • Nonlinearity
  • Small strain
  • Unsaturated soil

ASJC Scopus subject areas

  • Computational Mechanics
  • General Materials Science
  • Geotechnical Engineering and Engineering Geology
  • Mechanics of Materials


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