You will need a timber retaining wall deadman when the slope of the soil that the wall is trying to support is pretty steep. When this is the case, there is a larger tendency for the soil to push the wall down, because of its angle. Gravity will cause the soil to put more lateral pressure on the wall, hence the need for a deadman. It will be able to give some support at certain points of the wall, especially where the soil is most steep and applies the most pressure. A timber retaining wall deadman should be attached at least every 16 feet along the wall, in order to support its full length.