Retaining wall drainage can make a retaining wall incredibly strong or it can reduce the wall to a useless pile of rubble quite easily, so before building or planning a retaining wall, be sure to consider the best methods of retaining wall drainage. Specific plans for retaining wall drainage will vary according to the size, shape, and design of the wall, but every builder should remember that the most important aspect of drainage is to keep water from building up behind the wall, where it can cause cracking, sinkholes, warping, or other types of serious damage to the wall.
One can make effective retaining wall drainage systems by simply drilling holes in strategic locations, but these holes can quickly become clogged with sediment. It is important to consider the materials that will back-fill the wall. If soil is back-filled directly behind the retaining wall, drainage systems will become clogged quickly and potentially cause damage to the structure. Crushed stone should be placed directly behind the wall in between the wall material and the back-filled soil to prevent drainage openings from clogging. This layer of stone can also help prevent soil from becoming waterlogged and pressing solidly against the wall itself.
Retaining wall drainage systems will vary according to the materials used to construct the wall itself. A wall made from natural stone, for example, will essentially have a built-in drainage system, since the water will be allowed to seep out through the cracks between rocks. This type of wall is not the strongest, however, and water seeping out through the stones can cause stones to shift; the strength of the wall will therefore be unreliable. Wooden walls can be drilled for drainage; holes can be drilled at intervals throughout the base and middle section of the wall to allow water to seep through, but the water can cause damage to the lumber, and the holes can become plugged up without proper precautions taken during construction.
It is important to remember that retaining wall drainage, no matter how effective, can still cause damage to the wall and to the yard if the water is not redirected once it has left the wall. Some builders choose to guide the water toward already-established drainage ditches, while other builders must account for drainage where established drainage patterns do not already exist. Allowing water drained from a wall to pool at the base of the wall can cause just as much structural damage as allowing the water to pool behind the wall.