Explicit stress integration with error control for the Barcelona Basic Model. Part I: Algorithms formulations

Wojciech T. Sołowski*, Domenico Gallipoli

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

52 Citations (Scopus)


The numerical integration of the stress-strain relationship is an important part of many finite element code used in geotechnical engineering. The integration of elasto-plastic models for unsaturated soils poses additional challenges associated to the presence of suction as an extra constitutive variable with respect to traditional saturated soil models. In this contribution, a range of explicit stress integration schemes are derived with specific reference to the Barcelona Basic Model (BBM), which is one of the best known elasto-plastic constitutive models for unsaturated soils. These schemes, however, do not address possible non-convexity of the loading collapse (LC) curve and neglect yielding on the suction increase (SI) line. The paper describes eight Runge-Kutta methods of various orders with adaptive substepping as well as a novel integration scheme based on Richardson extrapolation. The algorithms presented also incorporate two alternative error control methods to ensure accuracy of the numerical integration. Extensive validation and comparison of different schemes are presented in a companion paper. Although the algorithms presented were coded for the Barcelona Basic Model, they can be easily adapted to other unsaturated elasto-plastic models formulated in terms of two independent stress variables such as net stress and suction.

Original languageEnglish
Pages (from-to)59-67
Number of pages9
JournalComputers and Geotechnics
Issue number1-2
Publication statusPublished - Jan 2010
MoE publication typeA1 Journal article-refereed


  • Barcelona Basic Model
  • Elasto-plasticity
  • Explicit stress integration
  • Richardson extrapolation
  • Runge-Kutta methods
  • Unsaturated soils


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