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ing screwing motion of the auger moves the materials to the end of the outer casing tube where the
material either falls off the end of the auger freely or can push the material out into the existing bentonite
mass. The maximum feed rate is actually 7 m 3 of granular bentonite material per hour. The
maximum filling volume of the steel cylinder was about 7 m 3 , resp. about 10 tons of granular bentonite
material.
As part of the testing, a comprehensive laboratory program was executed to investigate the performance
of the overall emplacement system. Bentonite samples were taken from each “big bag”
before filling into the auger for grain size distribution, water content and bulk density. After every
filling operation of the steel cylinder, the following parameters were determined:
• global bulk wet density
• particle size distribution measurements of the granular bentonite material before emplacement
out of the “big bags” and after emplacement sampled at selected points at the outer
surface of the steel cylinder
• water content measurements of the granular bentonite material before and after emplacement
In addition, other properties of the granular bentonite as mineralogy, swelling pressure, thermal
conductivity, etc. were determined in the laboratory of ETH Zurich (Switzerland) and Clay Technology,
Lund (Sweden).
Figure 3.3.3 Experimental setup (left) and emplacement of bentonite granulate with twin auger
system (right)
After each emplacement test, the bulk wet density of the whole steel cylinder was measured. The
bulk density is the net weight of emplaced buffer material over the total volume of the emplaced
bentonite. The bulk densities of the granular bentonite material show only small changes for different
admixtures of fine granular bentonite and coarse granular bentonite material. The water content
increased only slightly during the test runs from 5.0 % to 5.8 %. The results are very promising as
the required densities can be reached reliably (Nagra 2007 [4]). Figure 3.3.4 provides a summary of
the results.
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