A Concrete Retaining wall can be described as a structure that retains the lateral pressure – usually formed due to soil. In simple terms, it is nothing but a wall that holds the soil on one side of it so the desired changes of the ground level elevation can be achieved. A difference of Elevation levels can be seen on the either side of the retaining wall in the illustration. A basement wall, for instance, is a retaining wall.
Retaining walls can be made up of materials like stone masonry, timber, steel etc. However, the most common material is concrete for retaining walls construction owing to its durability, adaptability and availability. It can be moulded in to any shape and size, can be ordered from concrete plants or made on the site – also called insitu concrete retaining walls.
Concrete Retaining Walls
Concrete retaining walls can be of different types based on their working methods and type of construction. These include, but are not limited to, Gravity Wall, Cantilever wall, Piling Wall and Anchored Wall. On a smaller scale of retaining walls, which is where smaller lateral loads are applied, block retaining wall and sleeper retaining wall – made of concrete retaining wall blocks and concrete retaining wall sleepers respectively – are also common.
Gravity Retaining Wall
A gravity retaining wall uses its self-weight to counter the lateral loads coming from soil. For this reason, the gravity walls are usually big and therefore heavier as compared to other retaining walls. It can be used for retaining walls as high as 3 metres.
Construction is pretty simple and can be done with plain concrete only. A proper drainage system should be provided to avoid the lateral pressure caused due to the water in soil.
Although Concrete can be prepared on-site it is better to use the services of Commercial Concreting companies. The concrete provided is designed in a proper manner keeping the right amount of water, cement, fine and coarse aggregate along with any additives, if needed. They provide concrete based on Concrete’s compressive strength which is usually difficult to know when concrete is prepared on-site, unless very strict precautions are taken and a sample has already been checked in the lab.
Generally, the use of Commercial Concreting makes the construction of concrete structures much easier and more reliable.
Cantilever Retaining Wall
A cantilever retaining wall, as the name suggests, is based on cantilever technique where a slab is put underground to support the stem (see illustration).
Since the cantilever retaining wall is of a smaller section as compared to gravity walls, reinforcement is provided in normal conditions. Alternatively, Pre-cast concrete and Pre-stressed concrete can also be used for the construction. It can used for retaining walls up to 10 meters of height.
Construction, however, is not as simple as compared to gravity retaining walls. And, a suitable drainage system is provided to avoid to extra lateral pressure that would be caused due to the water available in soil.
Piled Retaining Wall
Piled retaining wall is nothing but reinforced concrete piles driven next to each other in the ground up to a certain depth that is enough to counter the lateral earth pressure. A gravel fill is usually provided for the drainage of water.
Sheet pile retaining walls are also used in a similar manner. These kind of piles can be used for the retaining walls which are up to 6 meters in height. The construction requires heavy machinery for the drilling or driving of piles in the ground. Construction is complex and therefore requires technical knowledge.
Anchored Retaining Wall
Anchored retaining walls are usually provided where a high retaining wall with a thin cross section is required. Wires or deep cable rods are driven deep sideways and then anchored by pouring concrete on to them. These tiebacks or anchors act against the sliding and over-turning of the retaining wall.
Similar to other methods, a drainage system is provided to avoid excess lateral pressure caused due to the water.
Gravity Retaining walls, Cantilever Retaining Wall and other described above are the kinds of retaining walls that are supposed to take high lateral loads. These kind of walls usually require an engineer and a technical team to design the retaining walls which would stand against sliding and over-turning failures.
Small retaining walls, usually up to 1.2 meters (4 feet), can be constructed and used on a private property with little expertise. All you’ll need is time and materials to construct these retaining walls. Such small retaining walls are constructed to hold back the garden soil and for other smaller lateral loads.
Concrete Block Retaining walls and Concrete Sleeper Retaining walls are possibly the best choices for such tasks.
Concrete Block Retaining Wall
A concrete block retaining wall is nothing but a set of concrete blocks stacked on top of each other. But, in order to make it a retaining wall that lasts for years and can take loads in a safe manner, some construction techniques should be utilized.
Concrete Block Retaining Wall Construction
First of all, a trench of certain height should be dug and compacted. A layer of crushed stone base, 15 mm 20 mm stones in size, should be provided. This requires less compaction and is good for the drainage.
Concrete blocks, or hollow concrete blocks, are then stacked in the form of a masonry so that all the joints should not come in the same vertical line. This would allow the retaining walls to resist vertical loads as well.
Depending on the concrete blocks you are using, the can come up with butt joints or locking flange to avoid sliding of one block over the other.
The same stones that we used for the stone base can be provided on the back of retaining wall for the drainage of water to avoid extra water pressure.
Concrete Sleeper Retaining Wall
Concrete Sleeper Retaining wall is very similar to concrete block retaining wall. In this retaining wall, concrete sleepers are used instead of concrete blocks. A number of companies provide factory-made sleepers and vertical posts.
Concrete Sleeper Retaining Wall Construction
Site should be cleared and levelled. Measurements should be made and auger holes should be dug for a depth of around 1.4 meters for a retaining wall of 1 meter height. A deeper hole would be required in case the retaining wall is higher than 1 meter. The posts should then be concreted into the ground so they are secure. A Concrete of around 20MPa strength would do the job.
Once the concrete is hardened and posts are in their proper place, sleepers should be paced. Seal the back of sleepers with a plastic sheet or with a concrete layer. A perforated drainage pipe should be provided to run along the length of wall. A drainage material such as crushed stone of around 20 mm in size should be provided over the pipe.
After the placement of sleepers, one should wait for around 7 days for the concrete to gain strength after which it is okay to pour the backfill material.
Three Best Types of Concrete Retaining Walls
Since there are different uses for each Concrete Retaining Wall mentioned in this text, it is difficult to choose the best three types. However, if we grade them based on their simplicity of construction, we can enlist three.
- Concrete Block Retaining Wall
- Concrete Sleeper Retaining Wall
- Concrete Gravity Retaining Wall
Afore-mentioned retaining walls offer simple construction methods and can be constructed without any technical assistance, if their usage is limited to private properties and shorter heights of around 1.2 metres.
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References and Further Reading