Journal of Earth Sciences and Geotechnical Engineering

Bentonite Homogenisation – Modelling of Homogenisation Processes in Bentonite Buffer Materials in Repositories

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• Abstract

  
  

  Swelling and homogenisation of bentonite materials are important functions of the bentonite to guarantee the requirements of the buffer and backfill after full water saturation in deposition holes and tunnels in a radioactive waste repository. A study including a laboratory testing programme with tests in different scales and complexity and modelling of the tests is financed by SKB. 

  In this article modelling of some of the laboratory tests with analytical methods and with finite element calculations is described and evaluated. The laboratory tests and the results are described in another article by Dueck et al .

  The FE-program Abaqus has been used to model four of the homogenisation tests with two different mechanical material models. Two different plastic material models (Drucker-Prager and Claytech Plastic Cap) have been used.

  Two fundamental tests with only axial or radial swelling were modelled to check the models and calibrate the parameters of the models. Both these tests were very well modelled with the Cap model but less good with the Drucker-Prager model. 

  Ten almost identical tests of the homogenisation of two bentonites with large density differences placed in long tubes with raw surfaces are running with the purpose to study long term homogenisation. One of those have been terminated and sampled and was modelled with an analytical solution. The results showed that the homogenisation was well captured if the residual friction angle evaluated from friction tests was used. Finally, homogenisation of a large bentonite block with two cavities was modelled with Abaqus. The calculation worked well but the model underestimated the self-healing ability.

  
  

  Keywords: Bentonite, homogenisation, modelling, swelling tests, void ratio, dry density, angle of friction.