If you wish, you can leave the drainage backfill slightly lower than the top of the wall, then fill the remaining space with topsoil for planting grass or other plants. The wider the backfill area with gravel or sand, the better your wall will drain.Ordinary soil can be far too dense, creating an enormous weight that puts dangerous stress on the wall. It is very important to use a porous material for backfill, as it will allow water to easily drain away, lessening the weight and force placed on the wall during heavy rains. When the wall reaches its completed height, carefully fill in the space behind the wall using sand or gravel.Wet earth is both hard to shovel into and hard to move. When to build: A retaining wall is best constructed when the soil is dry after a period of no rain.This design causes the wall to angle slightly back into the slope, further improving its holding power. A lip on the back of each block creates a uniform setback as each course is added. Designing the wall with a setback: Concrete retaining wall blocks are shaped in a way that creates a natural setback as the blocks are stacked.
For this reason, the space behind a retaining wall is usually filled not with soil, but with a porous, drainage-promoting material such as gravel or sand. Materials to fill the space: Soil becomes heavier when it's saturated with water.Drainage: A tall retaining wall may need to have a built-in drain pipe or other features to shed water and lessen the pressure on the wall.Our example, a three-tier wall with 14-pound blocks, weighs close to 500 pounds for each 8-foot stretch. But it's the blocks' accumulated weight that does the trick. (The blocks we used in our demonstration weigh 14 pounds each.) Some do-it-yourself retaining wall blocks weigh as much as 61 pounds. Heavy retaining wall blocks keep the soil at bay with their weight. The Spruce Home Improvement Review Board.