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It goes without saying that most new home building projects require a lot of digging. And every section of ground that is disturbed needs to be placed back to a grade that matches the engineered plot plan. Things like foundations, sewer and water lines, electric and gas services all require excavating into the earth to get them installed. Typically, if the backfilled area isn’t going to support a structure, it isn’t compacted. This will lead to settlement over time.
When is Backfill Compacted?
This is a standard practice in the home building industry in order to save money on the project. Backfill operations are typically not compacted. Exceptions to this include areas under concrete, asphalt or foundations that need to support a structural component…these are compacted to minimize settlement. The areas not compacted are those that will not affect other parts of the home. So, areas that are not typically compacted are around the perimeter of the foundation and other trenches for water, sewer, gas, and electric. These typically settle out over the first year and are filled at that time.
Avoid Building Decks and Patios in Backfilled Areas
If this is a big problem for you, discuss it with your contractor. Compacting these backfilled areas will involve extra machine time and labor so be prepared for an extra charge. If you decide not to go with the compaction, make sure you don’t place any patios or deck piers in these previously excavated locations. Over time the areas will settle, causing problems with your newly installed project.
How Much Will it Settle?
So what if you don’t compact the backfill? As long as there is no structural component supported by the disturbed soil, there really isn’t a problem. These areas will settle over time and will need to be filled with top soil. Things like fences and newly planted trees can settle and may need to be straightened as well.
The amount of settlement and timing of it depends on a number of factors including…
- Type of material being backfilled (example: stone compacts much better than dirt)
- Depth of Excavation: If you are digging an eighteen inch deep trench there will be minimal settlement but if you are digging an eight foot sewer trench…the settlement can be over a foot.
- Amount of rain or water the area gets: Water will help to compact the area and will speed up the settlement.
Speed Up Compaction with Sprinklers
Is there a way to speed up the settlement process of an already backfilled area so it won’t affect expensive landscaping installation? Yes and no. One way to speed up the natural compaction process is to put a sprinkler over the disturbed area and let it run. This will cause the soil particles to pack in more tightly and speed up the settlement process. Unfortunately, this is not an exact science so the amount of time required is a guestimate at best.
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