Download video: How to Dig a Foundation
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How to dig a foundation:
This video will help you understand how to dig for a footing or foundation.
step # 1 You need to determine the finish floor (F.F.) elevation of the pad or structure you are building. once you have determined the elevation, you can calculate the finish grade of the soil (F.G.) and then calculate the actual depth of your top of footing (T.F.)
Step # 2 Dig the foundation to the bottom of the footing. keep in mind you may need to shore the walls as the footings deepen with your existing grade. try to use the native soil as a form for your foundation, this way you can save time and money.
Step # 3 Verify the conditions of the soil, specially the bottom of the footing. although some Soil reports & structural drawings only ask to use the native soil (that means the un-disturbed soil) make sure that the soil is hard enough to support the footing. usually a visual test or a prove test can be used to determine the compaction on the soil.
However, there are occasions where the soil will have to be over excavated and brought back to elevation with compacted material. (typically done on soils where liquefaction is present.) like you saw on the video.