When you have built a retaining wall, you will need to calculate the amount of backfill required to support the wall. Backfill is meant to replace the soil which is excavated from the ground, and may include a soil or dirt, or even large rocks. When you are looking at your backfill, you need to ensure that there is no wood or vegetable matter in the backfill, as this may rot down and leave depressions around the retaining wall.
Step 1 - Calculate the Area
You will first need to work out the amount of space which needs to have backfill in it. This should be the width and depth of the gap between the edge of the The volume should be worked out by the depth times the width. You should then calculate how much of the area above the ground level you wish to fill. Remember that the backfill is used to support the bottom of the wall, so you will need a suitable amount.
Step 2 - Calculate Amount of Backfill
Take a small amount of backfill, and place it into a container such as a measuring jug. This will allow you to calculate how much (in weight) backfill you need to place into your (in volume) hole by the wall.