More than five centuries of mining activity in the area below the town of Idrija have caused major changes in the stress strain states of rocks and backfills in the affected areas of the mercury mine.
In past, before the mine closure works had approved, extensive numerical models were done by checked, proposed, grouted, and other consolidation measures supported by laboratory and in situ investigations in the goal to determine the geotechnical characteristics of rock mass and backfills.
Time-dependent occurrences of potential sliding areas on the surface and in mine rocks and subsidence of artificial backfills are still present, but the intensity of time-dependant movements is considerably reduced.
The deepest shaft which is now entirely closed with concrete backfill, reached a depth of 420 m at approx.
Pipe wear is reduced if the backfill is transported underground in pipelines.
This solution is the use of foam technology as it can produce a backfill with the combined benefits of both a paste and a hydraulic fill because the foam produces a 'pseudo' low density slurry making pipeline pressures low and reducing pipe wear rates during transport.
There is a significant decrease in compressive strength of backfill material that has not been subjected to de-foaming
For instance, a medium sized Canadian gold mine, operating at depths of about 1,350 m, has been using hydraulic tailings backfill but is consolidating its milling operations with another mine owned by the same company.
Finding better ways to mix, transport and place backfill materials is a high priority, notes Mike Rispin, MBT's mining manager.
New technologies are available that can compensate for logistical challenges, allow reductions in binder content while still achieving the desired placed properties, and even facilitate the use of backfill in areas containing dynamic water.
Due to the irregular nature of the cavern backfill accesses, the paste fill is dynamically adjusted for viscosity to facilitate filling of the cavern in a gradual, flowing, self-levelling manner from a single access located at an extremity of the opening.
Mines using cemented, backfill (or rockfill) often experience problems such as:
