A retaining wall is a structure that is used to retain a slope to avoid and eliminate unlevelled or unusable ground. In order for this to happen the area must be excavated. This involves cutting into the slope to provide a flat platform of ground. A retaining wall is then constructed to stop the ground from falling or caving in on the level platform that has been created. This is the biggest benefit from constructing a retaining wall. It can provide you with much more useable, practical and maintainable ground.
There are many different types of retaining walls. The three most commonly used are:
Timber Sleeper Retaining Wall
This wall is constructed from treated pine timber sleepers. The length of each bay and position of each post is usually no longer than 2.4m and the total wall height can be up to 1m high, any higher and engineering plans have to be drawn up. The depth of the posts is the most important thing. This is where the strength of the wall comes from. Posts should be cemented into the ground at least 600mm below ground level this is dependent on wall height. The hole should be twice the size of the sleeper used to ensure a sufficient amount of concrete is around each post. This will increase stability and strength of the wall. Once the posts are in the rails and then screwed on to the back of the posts. It is vital that drainage is installed behind walls as it keeps the wet soil and water build up off the timber, this increases the longevity of the wall. The life span of these walls is around 10-15 years before you start to see signs of rotting of the timber.
Link block Retaining Wall
This wall is constructed from link blocks. Similar to bricks, there are many styles, colours, and shapes of blocks and each type is suited to a particular circumstance, eg; some have the ability to curve where as others do not. The most important part of constructing a link block wall is the footer that the first course of blocks is laid on. They are laid on a compacted road base mixed with cement powder ensuring they do not sink and fall away. Once level the blocks will stack on top for as long and as high as desired. Drainage is also imperative in these walls as they will hold too much moisture and the soil will shrink and expand with the moisture creating pressure on the wall. Some types of blocks are hollow and can be core filled with a no fines concrete mixture which when set forms like honey Comb. This bond the blocks together to form one large block. These retaining walls have a longer life span then the timber walls, however are more susceptible to damage, such as the blocks chipping and cracking and the top course moving slightly.
Boulder Retaining Wall
This wall is constructed using large boulders or rocks. Once dropped or moved into place and then stacked on top of each other they form a simple but effective retaining wall. They can be as long as desired, however they must angle back into the bank slightly as you get higher to provide strength. The boulders should be laid in a brick like pattern to increase stability, depending on the grad eof blocks used, some may need mortar in the gaps, others can use wedges of the boulders.
After constructing the retaining wall of choice, the last but very important step is drainage. This means getting the water that gets trapped behind the wall out to a place where it will not cause problems. Before the rear of the retaining wall is filled in, a piece of Ag Pipe is put down flowing to the desired location and set at the correct angle. The size of Ag pipe depends on the size of the wall and incline of the bank you have retained. Once this is in it is then covered with a thick layer of drainage rock. Usually around 300mm and geo fab material. It is then covered with soil. This ensures the water will seep through and go into the pipe instead of remaining in the soil.