Journal of Earth Sciences and Geotechnical Engineering

Bentonite Homogenisation – Laboratory Study of Homogenisation Processes in Buffer and Backfill 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 some tests and test results from laboratory tests in different scales are described and analysed. The results have been used to evaluate parameters and models for modelling homogenisation as described in another article.

  A large number of fundamental very well controlled small-scale tests with simple geometries and swelling in radial or axial direction have been made. They show that homogenisation and healing properties of the investigated bentonites are extremely good but also that we have considerable density differences left.  

  Larger scale tests with more complicated geometries have also been done. In one of the test types swelling and homogenisation in long tubes have been studied with the purpose to study the effect of friction for limiting homogenisation. The other test type simulates loss of bentonite in two medium scale laboratory tests where a bentonite block with two large cavities were left to homogenise. The results show that the cavity has been very well healed by the swelling bentonite but also that the dry density in the centre of the former cavity is clearly lower than the density at the unaffected parts. 

  
  

  Keywords: Bentonite, homogenisation, radioactive waste, swelling tests, dry density, swelling pressure, angle of friction.