Colloid Formation and Migration - Phase 1 from 2004 to 2008

Phase 1 began in 2004 and ended early in 2008. The field activities focussed on site selection, site characterisation and site preparation. Predictive modelling and supporting laboratory programmes were conducted in parallel.

Photograph of the main shear plains of the test shear zone at AU96
Photograph of the main shear planes of the test shear zone at AU96 (to the east), previously referred to as migration or MI shear zone (red arrow spans approx. 100 cm of tunnel wall)


The shear zone at the experimental site was mapped in terms of its structural features and hydrological setting. Boreholes in place from the earlier MI, EP and CRR experiments and two newly drilled boreholes were used for the hydraulic characterisation of the site with hydro- and tracer testing. A series of preliminary tracer tests were performed in the shear zone to evaluate the suitability of flow fields for the colloid migration experiment by:

  • Assessing the advective travel times
  • Analysing the recovered tracer mass
  • Estimating dispersion parameters in the shear zone flow fields

Detailed geological mapping of the test shear zone between tunnel meters AU93 and AU100 with surface-packer locations
Detailed geological mapping of the test shear zone between tunnel meters AU93 and AU100 with surface-packer location

The most challenging site preparation task was the sealing of the tunnel surface. Sealing resin applied directly to the tunnel surface did not withstand the high hydraulic heads in the shear zone. After various considerations it was decided to install a steel tube of 5 m length with large “o ring type”, cement-filled Bullflex packers at each end.

Simplified design and functional principle of the megapacker installed to seal the tunnel surface.

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Short video of the megapacker installation in October 2006

The surfaces of the Bullflex packers facing the open tunnel are sealed with a resin cover in fall 2007
The surfaces of the Bullflex packers facing the open tunnel are sealed with a resin cover in fall 2007
in an effort to solve leakage problems

The CFM laboratory group focussed its Phase 1 activities mostly on the following issues:

  • Colloid generation (physical erosion, geochemical alteration etc.)
  • Colloid transport/retardation and stability (filtration effects, sedimentation, groundwater chemistry)
  • Radionuclide association (colloid-radionuclide binding, reversibility, radio-colloids)
  • Bentonite intercomparison (MX-80, Febex, Kunigel)

The CFM modelling group spent the majority of its efforts on:

  • Supporting the in-situ tests
  • Initiating performance-assessment relevant studies on colloid generation and on colloid-facilitated radionuclide transport (including the irreversibility of sorption and matrix diffusion/filtration effects)

 

Colloid Formation and Migration Experiment

The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.
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