Challenges of Simulating Undrained Tests Using the Constant Volume Method in DEM

Kevin J. Hanley*, Xin Huang, Catherine O'Sullivan, Fiona Kwok

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Liquefaction during earthquakes can cause significant infrastructural damage and loss of life, motivating a fundamental study of undrained sand response using discrete element modeling (DEM). Two methods are widely used in DEM for simulating the undrained response of soil. One approach is to numerically couple the DEM code with a fluid model. Alternatively, if the soil is fully saturated and water is assumed to be incompressible, the volume of the sample can be held constant to simulate an undrained test. The latter has the advantage of being computationally straightforward, but the assumption of a constant volume can cause some issues which are discussed in this paper. Depending on the contact model selected, extremely high deviatoric stresses and pore water pressures can be generated for dense samples using the constant volume approach which are not observed in corresponding laboratory tests. Furthermore the results of these constant volume simulations tend to be sensitive to the strain rate selected. The evolution of particle size distribution caused by grain crushing is also ignored in most undrained simulations. For these reasons, authors often restrict the extent of the data presented to physically-realistic ranges and report results in non-dimensional terms, e.g., using stress ratios (q/p') or stresses normalized by the initial confining pressure. This paper aims to highlight some of these issues, explore whether the constant volume approach is appropriate and make recommendations for future analysis of undrained soil behavior using DEM.

Original languageEnglish
Title of host publicationPOWDERS AND GRAINS 2013
EditorsA Yu, K Dong, R Yang, S Luding
Place of PublicationMELVILLE
PublisherAmerican Institute of Physics
Number of pages4
ISBN (Print)978-0-7354-1166-1
Publication statusPublished - 2013
Externally publishedYes
Event7th International Conference on Micromechanics of Granular Media (Powders and Grains) - Sydney, Australia
Duration: 8 Jul 201312 Jul 2013

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X


Conference7th International Conference on Micromechanics of Granular Media (Powders and Grains)


  • Discrete element modeling
  • undrained simulations
  • pore water pressure
  • strain rate dependence


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