To prevent downslope soil erosion, different retaining walls are built. These walls hold back soil from buildings, structure or a particular area. This article presents a brief insight into such types of walls.
The build of retaining walls consists of materials like masonry, stone, brick, concrete, vinyl, steel or timber. Certain areas have topography that varies from slightly rolling to mountainous. For such areas, retaining walls allow the construction of steps or level areas.
Retaining walls had been used by ancient Roman civilization in the construction of roads. Their extensive use can be found in many castles in Europe as well. Since then, there were many types of retaining wall construction which have been used and improved over time.
Gravity walls use their mass or weight to resist the pressure exerted by the earth behind them. These walls usually have an average height of three to four feet. They are made from mortar-less stone or masonry units.
Gravity is able to hold back the earth or soil, due to its construction. These walls consist of a volume of materials. These materials are stacked together in the making of the walls. The weight or force of friction that is created by these materials is greater than the force exerted by the soil. The thickness of the wall at the base exceeds that at the top. A process known as ‘battering’ helps the walls to improve stability by leaning back into the retained soil. In this process, as the walls get taller they slant backwards. Battering is done to prolong the lifespan of gravity walls, which otherwise would tilt outward. Construction of gravity walls demands a high quantity of building materials. That is the reason these walls are difficult to build, and get more cumbersome as they get higher.
Cantilever Retaining Walls
Cantilever walls are among the taller retaining walls, and are single layer walls. Here, the walls have uniform thickness and are tied to a footing. Properly engineered cantilever walls hold back sufficient amount of soil. Typical basements in a house are an example of these retaining walls.
Cantilever walls are manufactured in the form of an inverted ‘T’. The word ‘cantilever’ means ‘projecting horizontal beam fixed at one end only’. Here, it means that the walls transform horizontal pressure from behind the wall into vertical pressure on the ground below. The footer of cantilever walls should be wide enough to prevent the wall from tipping. The thickness of not only the footer but also that of the wall is important. The walls are built with steel-reinforcement in both the footing and wall structures. Cantilever retaining walls are and should be designed only by structural engineers. They are not meant for self-building purposes.
Sheet Piling Retaining Walls
For areas having soft soils and tight spaces, sheet piling retaining walls are mostly utilized. Materials such as steel, vinyl or wood planks go into the making of these types of retaining walls.
The statistics of the walls include one-third portion above the ground and the rest (two-third) below ground level. A cable or a rod is used as a tie-back anchor to the walls. The rods are placed at a distance and tied to the back of the walls. Hydrostatic pressure is one of the main causes of the instability of the walls. So to eliminate this drawback, proper drainage has to be ensured during construction.
Counterfort Retaining Walls
Counterfort retaining walls are similar in construction to cantilever walls. However, these types have one additional benefit in the strength provided by triangular walls.
The top of the wall and the back of the footer are joined by these triangular structures. The three structures of the footers, retaining walls and the additional walls are incorporated by reinforcing steel. The support provided by the triangular wall extends the durability of the counterfort retaining walls. This is because the additional support keeps the walls attached to the footers. These retaining walls also are best built by engineers only.
Concrete Retaining Walls
These types are common in gardens and other outdoor landscapes. They offer better support for vertically-slanting slopes.
Concrete retaining walls are high-built and have deeper and heavier soil underneath them. These properties make them offer better resilience and solidity. These walls require greater base depth so as to create a better foundation. Properly installed concrete retaining walls do not face problems like tilting, bowling or cracking. They are also not susceptible to climate-induced degradation.
Block Retaining Walls
For enclosing an area in a garden, block retaining walls are the most suitable. These walls are of two types. Modular retaining walls, and segmental retaining walls. They have interlocking concrete units to hold back the load of the soil. Similar to gravity walls, they use the force of gravity to resist overturn and sliding. The nature of the walls prevents hydrostatic pressure as well.
Rock Retaining Walls
For leveling flower beds in gardens, you might consider installing rock retaining walls. The rocks and stones that are used in the construction of these walls must suit the landscape.
When rocks are stacked together, spaces are left between the rocks. These spaces or gaps are filled with the soil mix. If plants are allowed to grow in between the rocks, it will strengthen the walls. Growing roots will prevent soil from becoming loose, and help prevent soil erosion.
Cinder Block Retaining Walls
Cinder block are also used for retaining walls and gardens. Here, the cinder blocks are reinforced with steel bars embedded in a concrete foundation.
The wall is built upon a 1-foot deep flat-boxed shaped trench. The foundation is double in size than that of the trench. The steel bars are placed in the form of an ‘L’ shape. The cinder blocks are placed using mortar and a trowel. As cinder blocks are hollow, the steel bars rise through them when the blocks are laid. Post construction of the walls, facades of stones or bricks may be added to make the walls attractive. This is done by most people, as cinder blocks are not so attractive.
Terraced Retaining Wall
Those who have yards with deep slopes usually have a hard time growing plants or install architectural structures on them. For such uneven landscapes, terraced retaining walls fit the bill.
An internal tie system helps in bracing the walls and locking them in position. There is no limit to the height of the wall, as it is the width that decides the installation. Materials that can be used include concrete blocks, timber, brick
or natural stone blocks. Such walls can be put to use in various creative ways. One good example could be retaining water and making it a small pond filled with fish and water plants.
As you can infer from the above description you have a wide variety of retaining walls to choose from. Keeping your landscape in mind, go for a suitable retaining wall. And as mentioned earlier, it is wise to hire professional structural engineers for the job.