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Backfill is mainly natural material that is used to fill in some void left after construction or excavation efforts. Usually, the backfilling is a combination of stone, soil and other materials that were left over after the main portion of the project was completed. However, the backfill may be transported to the building site if necessary.
There are several different applications in which the process of backfilling is useful. One has to do with maintaining the integrity of a mine. When ore or precious metals are extracted from the mine, backfill materials are used to fill in and patch the areas where the digging took place. This process helps to keep the mineshafts stable and relatively safe for future excavation efforts by limiting the possible after effects of seismic activity in the immediate area.
It is also common to backfill the area immediately around the foundation of a building, such as a home. Using the compacted earth and stone that was excavated in order to create a smooth site for the construction of the building, the backfilling is piled against the finished foundation. The result is that water will tend to flow away from the foundation and help minimize the chances of the rapid deterioration that would lead to weakening the entire structure.
Backfill may also be used to fill a trench that was created for some purpose, but is no longer required. By pushing loose soil and stones back into the trench, it is possible to level out the area once again, especially if heavy equipment is used to pack the backfill tightly. Since the materials in the backfilling are usually natural, the area can also be seeded, allowing grass or plants to easily take root and cover the area where the trench was once situated.
Drilling operations sometimes make use of backfill as well. Once the pipes are set in place for a well, the soil and stones removed as part of the installation can then be placed back around the exterior of the pipe. The packed soil helps to stabilize the pipe and lessen the opportunity for the pipe to bend under pressure during usage.
In most situations, the use of backfill is not only environmentally friendly, but also very practical. The materials that make up the fill are usually excavated from a nearby location and would have to be hauled out of the area if not used. In addition, usage of the loose materials means that synthetics do not have to be purchased and hauled into the area to achieve the same results. From this perspective, backfilling helps to save time and money, both of which are important when engaging in any type of building, landscaping, or mining operation.
I know sometimes a landscaper or contractor will want to backfill a hole with something other than the original material. I've helped homeowners backfill post holes with concrete or gravel instead of the dirt surrounding the hole. The original material may not offer enough stability for a weight-bearing post or enough drainage for a buried pipe.