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

摘要

Swelling and homogenisation of bentonite materials are important functions of thebentonite to guarantee the requirements of the buffer and backfill after full watersaturation in deposition holes and tunnels in a radioactive waste repository. A studyincluding a laboratory testing programme with tests in different scales andcomplexity and modelling of the tests is financed by SKB.In this article modelling of some of the laboratory tests with analytical methods andwith finite element calculations is described and evaluated. The laboratory tests andthe results are described in another article by Dueck et al [1].The FE-program Abaqus has been used to model four of the homogenisation testswith two different mechanical material models. Two different plastic materialmodels (Drucker-Prager and Claytech Plastic Cap) have been used.Two fundamental tests with only axial or radial swelling were modelled to checkthe models and calibrate the parameters of the models. Both these tests were verywell modelled with the Cap model but less good with the Drucker-Prager model.Ten almost identical tests of the homogenisation of two bentonites with largedensity differences placed in long tubes with raw surfaces are running with thepurpose to study long term homogenisation. One of those have been terminated andsampled and was modelled with an analytical solution. The results showed that thehomogenisation was well captured if the residual friction angle evaluated fromfriction tests was used. Finally, homogenisation of a large bentonite block with twocavities was modelled with Abaqus. The calculation worked well but the modelunderestimated the self-healing ability.