Retaining walls are by nature designed to hold back slopes of earth. An improperly engineered retaining wall can fail for a number of reasons such as poor drainage or design flaws. A failed retaining wall is an eyesore and can pose a danger. Properly reinforcing a wall avoids failure, the cost of rebuilding the wall or any ensuing damage if the wall does happen to fail due to improper reinforcement techniques.
Determine the type of wall to be installed. There are several types of retaining wall available, including timber, plain concrete, interlocking block, dry brick and stacked stone. The slope to be retained, the height of the wall and the soil in the area are all factors to be considered. A severe retention such as a high slope or soil with poor drainage needs a more securely engineered type of wall with proper drainage. A minor slope with a more aesthetic use can utilise a simpler method such as stacked block or stones without much concern.
Prepare drainage, and a footing if required. Concrete walls require a footing, and all retaining walls should have a drainage trench with a perforated drainage pipe covered in gravel to eliminate groundwater from washing the wall out. A trench is dug and landscape fabric laid in the trench to keep sediment from rising and filling the drainage pipe. Gravel is laid in a 10 cm (4 inch) deep layer so that it is below the frost line. The 10 cm (4 inch) perforated drain pipe is laid at the base of the wall and covered with gravel.
Build a concrete retaining wall on a footing reinforced with rebar. The footing needs to be built over a gravel drainage bed. Place rebar within the footings, then stack the concrete breeze block above, filling the voids with concrete when complete. All retaining walls need to be placed so they lean 2.5 cm (1 inch) into the hill for every 30 cm (12 inches) in height.
Stack the interlocking block walls for a retaining wall of less than 1.2 m (4 feet) in height according to the manufacturers instructions. This type of wall has blocks that interlock, some of which have backfill traps which are filled with soil to assist in reinforcing them. The reinforcement for these types of walls is the design of the blocks and tiebacks, if recommended, made to interlock and naturally lean into the hill, the tiers are backfilled at each level so the soil is compacted properly behind the wall. Tiebacks are pieces of metal bar or webbing that lock between the blocks and extend back into the hill and are buried in the soil, helping to secure the wall.
Construct timber walls with an engineered plan. This type of wall is more prone to failure and should be carefully constructed using deadman anchors that are tied into the timbers and extend into the hillside at a distance of about 1.8 m (6 feet). Deadmans anchors are built by tying a horizontal timber into the hill with a cross piece nailed to its end parallel to the wall. Backfill at each level to compact the earth properly behind the wall. Built over drainage as all other types of walls, the timber wall employs 30 cm (12 inch) spikes driven into predrilled holes in the timbers. The timbers need to be carefully cut and squared to ensure proper fit to avoid premature failure of this type of wall.