Retaining Walls:

What are Retaining Walls used for? Retaining walls are used for stabilizing and controlling erosion of steeply sloped areas of the lot. In some cases, retaining walls are used in conjunction with terracing to provide a level area for recreational purposes. In either case, they should be designed to withstand the lateral pressures being exerted on them, by the soil and the hydrostatic pressures from behind the wall.   Retaining walls may be built with concrete, construction timbers, railroad ties, stone, concrete or concrete blocks. Some concrete and concrete block walls have stone or brick veneer facings. On occasion, you may find a retaining wall of steel baskets filled with stones. This is referred to as a “gabion” retaining wall. As the gabions age, the steel baskets tend to corrode and deteriorate, especially on the side facing the embankment. Over the years, the stone inside may begin to move.   The design of the retaining wall should incorporate provisions for drainage of water that normally accumulates behind the wall. Otherwise, the hydrostatic pressures built up will cause structural failure of the wall. Drainage may be provided by installing continuous perforated drain lines at the lower portion of the wall, and backfilling the areas with stone and gravel. In concrete retaining walls, the perforated pipe is replaced by weep holes in the bottom of the walls that allow the water to exit through the front of the wall. The grade or soil at the base of the drainage system behind the wall should direct any water that accumulates to the weep holes. Unfortunately, retaining walls are often built with inadequate drainage provisions. The gravel backfill or the drain line may be omitted, or the weep holes may be too few or too small to be effective. The weep holes should be kept clear so that the water behind the wall can adequately drain.   A retaining wall built with construction timbers or railroad ties should be anchored to the hillside to provide resistance to the lateral forces. If the wall is not tied back into the earth, it can bow, buckle or heave and eventually collapse. Anchoring the wall is achieved by using tiebacks or dead-men.  A tie back is a construction timber that is placed perpendicular to the wall. The front end is flush with the wall and is fastened to the wall itself with large spikes. The rear end is fastened to a dead-man or a small section of lumber perpendicular to the tieback and parallel to the wall itself. Because the construction timbers and railroad ties have open spaces between the members, weep holes may not be necessary.   Many railroad tie and timber retaining walls are not constructed with anchors. You can tell whether anchors were used by looking at the wall. If tiebacks were used, end sections will be visible in the face of the wall. However, from a visual inspection you cannot determine the length of the tie back or whether dead-men were, in fact, installed. All retaining walls should be vertical or inclined slightly towards the embankment. They should not be leaning forward or away from the embankment. When you encounter a retaining wall that is leaning, it is an indication that the wall has not withstood the lateral forces that have been exerted. Once the wall begins to lean, crack and heave, the pressure that caused its condition should be relieved.

Retaining Wall Design:

Retaining walls are used to give support to vertical sloping land. By installing retaining walls, such sloping land can be leveled and hence be of greater use. Plants, trees and gardens can be incorporated, to once useless land.

Retaining walls also have a less functional use, which is a visual or decorative purpose. Retaining walls can be used in the garden to add to the landscaping design, such as surrounding flower beds or to accentuate feature gardens.

With the use of colored bricks and pavers, decorative stones and various timbers, retaining walls can add that aesthetic appeal to the garden grounds.

Retaining walls are also used for the construction of highway walls, parking lots, erosion walls and bridges.

Factors to Consider in Building a Retaining Wall:

Building a retaining can be easy enough for do-it-yourself installation, however the higher the slope the more difficult it becomes to construct. When the slope of the land becomes too high and steep, a structural engineer is required. The reason for this is that many structural factors must be taken into consideration and resolved to prevent destabilization of the wall.

So the gravity of the situation where a retaining wall is being considered is very important. The retaining wall has to be able to do the same job that the soil presently does. Therefore the type of soil behind the wall must be considered, or better yet a drainage system can be put in place. This will allow water to be released from behind the wall, and hence put less weight pressure on the wall.

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