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Workreport 2018-10

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Name:

Testing Backfill Performance Under Early Inflow in a 1:6 Scale Deposition Tunnel Test Device

Writer:

Martikainen, J., Marjavaara, P., Leino, T.

Language:

English

Page count:

196

Summary:

This report describes laboratory tests and analyses regarding backfill wetting at early times after installation using a three-component backfill design (floor layer, backfill blocks and gap-filling pellets). A custom-made, pilot-scale deposition tunnel test system was designed and manufactured to carry out this work. Five backfill tunnel tests were performed using a 2-m long test device at a 1:6 scale (with respect to height of the backfill tunnel) against a constant inflow rates of 0.05 and 0.1 L/min.

Initial water infiltration behavior in a deposition tunnel was simulated by pumping a saturating solution (total dissolved solids 10 g/L) through a 6 mm (inner diameter) pointwise inlet into the tunnel test system at a constant rate over the course of the tests and early wetting processes were examined. The onset and extent of backfill material wetting and saturation, susceptibility to erosion, channel formation/sealing, density homogenization and swelling pressure developments were the areas of interest.

Backfill performance under early inflows was studied under the following water inflow conditions; tunnel wall wetting, tunnel crown wetting and floor wetting (simulating inflowing water from a deposition hole) using German clay or Greek bentonite as backfill block materials and Greek bentonite as pellet material (in the pellet-filled gap and foundation layer).

Erosion, channel formation and early wetting pattern processes were found to be mainly dependent on the water inflow conditions (inflow port location). Inflow port locations underneath the foundation layer and block line gave rise to upwards flow through a block-block seam (above the inlet port) resulting in substantial block erosion. The overall inflowing water migration progressed towards the tunnel ceiling after only a limited wetting along the deposition tunnel wall or floor. No significant backfill system density homogenization due to block expansion over the course of the tests was observed. Swelling expansion of pellet material into mass loss regions in block volumes, and vice versa, was observed. Additionally, the sealing of flow channels through pellet zones was seen.

Keywords:

Backfill performance, foundation layer, backfill blocks, pellet filling, early inflow, initial state, wetting behaviour, erosion, swelling pressure, density homogenization, self-sealing, Greek bentonite, German clay, pilot-scale deposition tunnel test system

File(s):

WR 2018-10_web (pdf) (19.4 MB)


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