Development of Backfill Material

One of the focal areas in the development of tunnel backfill is the joint performance of the block- pellet construction in the conditions prevailing in the disposal tunnel. The detail design of the block and pellet manufacture and installation processes is also about to start.

Investigations have particularly concentrated on the migration of water in the backfill material as well as on phenomena related to channelling taking place in the interfaces of the backfill materials. Experiments on these have been carried out both on laboratory scale and in field conditions in Finland and Sweden but full-scale tests are yet to be carried out.

Tests on backfill materials have been performed for more than a decade, but with the introduction of prefabricated blocks of backfill material to be used instead of in-situ compaction of the material, the number of tests has increased. There are several alternative materials and laboratory tests have been carried out on many parallel natural swelling clay materials and mixtures of swelling clay and aggregate material.

Miniature concrete tunnels have been built for small-scale field tests to allow the installation of the backfill material to be practiced and the performance of the material to be studied after installation, when water is run into the miniature tunnel.