Tactic TR-12: Backfilling
Use backfilling to help stabilize the thermal balance at the tundra surface. The addition of soil can lower the rate of heat transfer into underlying permafrost. If the site remains stable, subsidence of the ground surface caused by thermokarst will be minimized, helping to prevent the impoundment of water and increasing the number of options for revegetation. Backfilling may not be necessary if tundra sod (Tactic TR-10) is added (Fig. 117); sodding is similar to backfilling because relatively thick (6–12 inches) pieces of tundra sod can provide insulation to protect permafrost. Tundra sodding has the added benefit of immediately increasing the plant cover at a site.
Mineral and organic overburden from a mine site often is used as backfill material (Fig. 118). Add enough backfill to allow for settling. Also, the soil may have a high content of ice; add enough backfill material to ensure the volume of soil added will be sufficient after the ice melts. Backfill should be added in lifts. Lifts of backfill should be compacted periodically to minimize settlement.
Considerations and Limitations
- A Material Sales Contract with Alaska Department of Natural Resources Division of Mining, Land & Water, is needed to use overburden from a mine site as backfill.
- Plywood walkways should be set up at the site in order to reduce damage to the adjacent tundra.
- Use of vehicles and heavy equipment on tundra must comply with applicable tundra travel policies (Tactic P-5).
- Surface water should be removed before backfilling.
- Testing may be necessary to determine backfill material properties such as particle size, relative amounts of gravel, sand, and silt.
Equipment, Materials, and Personnel
- Plywood walkways (2 workers) – to prevent trampling of tundra.
- Wheelbarrow (1 worker) – to haul backfill material.
- Bobcat or front-end loader (1 operator) – to collect and transfer soil used for backfill.
- Dump truck (1 operator) – to transfer backfill material to the site for rehabilitation.
- Wooden lathe - for staking depth of backfill material needed.