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Recent publications

Workreport 2020-8



Uniaxial Compression for Bentonite Backfill Blocks: from Lab to Factory Scale


Holt, E., Sjöblom,V., Fortino, S., Koskinen



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This report is published only for Posiva's internal use.

This report summarises manufacturing of backfill blocks from two materials, Ibeco RWC-BF and Friedland clay (0-1mm), at compaction loads of 25 to 50 MPa. 

Nearly 100 small-scale 100 mm diameter samples were produced with dual-direction compaction, at varying water contents and with varying mould and filling parameters, to establish the best methods and materials to obtain the high target dry density to fulfil design.

A new medium-scale mould was designed, including rounded corners based experiences about previous block pressing tests, as well as modelling of friction and density. Then approximately 20 medium-scale (half the dimensions of Posiva’s reference backfill blocks) Ibeco RWC-BF and Friedland clay (1-6 mm) blocks were produced in the lab. The Friedland blocks achieved the target dry density of 2050 kg/m3 at a water content of 10%. Optical microscopy studies were done to understand the variation in Ibeco RWC-BF material. 

The results from small and medium-scale trials were then applied in factory conditions with compaction of Ibeco RWC-BF done at approximately 23 MPa. A total of 11 blocks were produced, with the achieved dry density of 1680 kg/m3 at about 16% water. The compaction factor for the materials ranged from 1.5 to 2.0, which required a two-stage filling and compaction process due to volumetric limitations of the factory equipment. According to the tensile and compression strength analysis, there were no systematic weak points in the blocks.

The results of this work done in 2011-2012 were used in the backfill design work and in preparation for full-scale backfill deposition trials.


bentonite; uniaxial; compression; backfill; laboratory; block; small scale; medium scale; large scale; factory; modelling



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