Work package #4

Laboratory testing


  • provide input data and parameters for development and validation of models (WP3, WP5)
  • reduce uncertainties about conditions and phenomena influencing bentonite homogenization, through experimental studies

Description of work

A whole range of conditions and phenomena will be crucial for the evolution of the buffer and will have to be evaluated.

Initial state of the buffer: For buffer homogenisation or, on the other hand, the evolution of heterogeneity there will be a difference between initially single density (i.e., a bentonite block) or multi-density (pellets, blocks/gaps, blocks/pellets) systems. In this context, the scale of observation is important (a pellet system might be considered as homogeneous in the large scale, while being highly inhomogeneous on the pellet scale).
Hydration conditions and history: Solution composition, thermal and mechanical load and hydration history will have an impact on the evolution of buffer texture, swelling pressure and hydraulic properties.

Interplay between heterogeneity and swelling pressure as well as mechanical properties: Evolution of heterogeneities in the buffer will possibly affect the overall swelling pressure and mechanical properties, e.g., shear strength. Especially at interfaces, e.g., between buffer and waste package, shearing behaviour can be relevant with respect to the homogenisation process.

The task of this work package is to complete the respective data and to provide support and parameters for advanced material models. The work is divided into three tasks:

  1. Task 4.1: Investigation of the homogenisation of an initially inhomogeneous bentonite system
  2. Task 4.2: Persistence or development of inhomogeneities in the bentonite system under various mechanical and hydraulic conditions
  3. Task 4.3: Natural analogues

The experiments have to be designed in a way that they can feed directly into WP3 and WP5, and a close cooperation between the WPs is needed. Therefore, planning sessions of WP4 together with WP3 and WP5 partners will be held regularly with the annual meetings. Also, timing and content of the deliverables will be tuned to those of WP3, although results will be transferred to WP3 and WP5 as they are obtained.

Different bentonites are investigated to broaden the spectrum of observations. On the other hand, different analysis techniques will be applied by different partners, so that a more complete and reliable characterization of bentonite behaviour is obtained. This will improve the reliability of data needed for model development (WP3) and model validation (WP5). The following work is planned in the individual tasks: