Retaining walls are rigid structures designed to support soil laterally so that it can be held at various heights on the two sides. The purpose of retaining walls is to hold soil to a slope that it would not naturally follow (typically a steep, near-vertical, or vertical slope). They are frequently utilized in terrain with unfavorable slopes or in regions where the environment needs to be drastically changed and constructed for more specialized purposes, including hillside farming or traffic overpasses. A seawall or bulkhead is a retaining wall that retains soil on the backside and water on the front.

A retaining wall is designed to hold certain items in place, such as the edge of an excavation or a terrace. The structure is made to withstand the lateral pressure of soil when the required change in ground elevation exceeds the angle of repose of the soil.

The most important component of effective retaining wall design and construction is recognizing and thwarting the tendency of the trapped material to move downslope due to gravity. As a result, there is lateral earth pressure behind the wall. The magnitude and direction of this movement, as well as the angle of internal friction (phi) and cohesive strength of the held material, all affect how much movement the retaining structure experiences.

At the top of the wall, lateral earth pressures are zero, and in uniform ground, they rise proportionately to a maximum value at the lowest depth. If the problem is not solved, earth pressures will force the wall forward or cause it to collapse. Moreover, hydrostatic pressure on the wall is caused by any groundwater behind the wall that is not eliminated by a drainage system. For lengthwise sections of uniform height, the whole pressure or thrust may be assumed to act at a third from the lowest depth.

To keep the pressure within the wall's design value, effective drainage is essential behind the wall. The hydrostatic pressure will be reduced or eliminated by drainage materials, which will also increase the stability of the material behind the wall.

 Types of Retaining Walls

Retaining walls can be classified into several categories based on their structure, materials, and construction methods. Here are some common classifications of retaining walls:

By Structure:

Gravity retaining walls

Reinforced retaining walls

• Cantilever retaining walls

• Counterfort retaining walls

• Precast retaining walls

• Pre-stressed retaining walls

 Classification by materials

• Concrete retaining walls

• Masonry retaining walls

• Stone retaining walls

Reinforced soil walls

• Reinforced soil

• Soil nailing

Hybrid System

• Anchored earth retaining walls

• Tailed gabion walls

Sheet pile walls

Gravity Walls

Gravity walls use their enormous weight to hold the material behind them and establish stability against breakdowns. A gravity-retaining wall can be built out of brick, stone, or even concrete. Gravity-retentive walls are much thicker in section. These walls’ geometry aids in their stability as well. Walls made of mass concrete are appropriate for retained heights up to 3 m. The wall’s stability, how it uses the area in front of it, the required wall appearance, and the construction technique all have an impact on the cross-sectional shape of the wall.

Reinforced Retaining Walls

On spreading foundations, reinforced concrete and reinforced masonry walls are gravity structures whose stability against overturning is given by the weight of the wall and its reinforcement bars. The most common wall types are as follows:

Cantilever Walls

A wall that is attached to the foundation is a cantilever retaining wall. A cantilever wall must be carefully designed because it holds back a lot of soil. They are the kind of retaining wall that is most frequently used. Cantilever walls are supported by a block of ground. The weight of the backfill and surcharge, which is also loaded onto this slab base, stabilizes the wall against toppling and sliding.

Counterfort Walls

Counterfort walls are cantilever walls that are reinforced with monolithic counterforts made of the base and rear slabs of the wall. The counter-forts link the wall slab and the base and serve as tension stiffeners to lessen bending and shearing stresses. Counterforts are employed to decrease the bending moments in tall vertical walls, with their spacing being equal to or slightly greater than half the height. For high walls over 8 to 12 meters high, counter forts are used.

Precast Retaining Walls

Precast retaining walls are concrete structures vibrated to retain soil. They are made up of a row of full-height modular plates. On the side that is exposed to the soil, there may be one or more vertical strengthening ribs that run from the base of the wall to its peak. They can be positioned atop a prefabricated foundation of different sizes that has already been built. The two parts are then held together using a concrete pour.

Prestressed Retaining Walls 

For the purpose of constructing a continuous, consistent concrete retaining wall, prestressed concrete panels are often laid between steel columns. Because of its distinctive design, pre-stressed concrete is intrinsically stronger than conventional concrete. Before installation, panels are crushed and tensioned using steel tendons, making the concrete panels more resilient to tension. Also, this lessens the chance of the concrete cracking.

Masonry Retaining Walls

A masonry retaining wall is a construction made of materials like stone that is intended to keep dirt, rock, and other materials in place. The term “masonry” refers to a construction method in which material blocks are piled and cemented together. Stone, brick, glass, ceramic, concrete blocks, and other materials are examples of these materials. A well-constructed stone retaining wall has the potential to be both extremely durable and visually appealing.

Reinforced Soil Walls

This category comprises reinforced soil and soil nailing and includes walls that use soil that has been reinforced with reinforcing bars to form a sturdy earth retaining system. Reinforced soils can be used to construct retaining walls in the following ways:

• As an essential component of the design.

• As an alternative to the use of reinforced concrete.

• To serve as temporary works.

• As repairs or upgrades to an existing configuration.

Soil Nailing 

When building a soil-nailed wall, the earth is reinforced as excavation continues by the addition of passive bars, or bars that essentially work in tension. Typically, they run parallel to one another and are slanted downward. These bars can also function partially under shear and bending.

Hybrid System

Hybrid or Composite retaining wall systems are the kind of retaining walls that rely on both their mass and reinforcements for stability. They include the following:

Anchored Earth Retaining Walls 

An anchored earth wall is any structure that uses facing components fastened to rods or strips with the ends anchored into the ground. Similar to abutments are the anchors. Often, high strength, pre-stressed steel tendons are employed as the tying cables. The ends of the strips are shaped to bond the strip at the point into the soil in order to enhance anchorage.

Tailed Gabion Walls

In civil engineering, road construction, military applications, and many other fields, gabions are cages, cylinders, or boxes filled with soil or sand. Rip-rap with cages is used to control erosion, while metal constructions are employed for creating foundations or dams.

Sheet Pile Walls

Steel sheets are driven into an excavation or slope until they reach the desired depth to create steel sheet pile walls. Their most frequent application is in short-term, deep excavations. They are thought to be most cost-effective in situations when soft soil retention at greater earth pressures is required. It is unable to withstand extreme pressure.

Functions of Retaining Walls

Retaining walls provide a variety of advantages that can help turn your environment into a beautiful and useful work of art. They are;

Structural Support

The purpose of a retaining wall is to hold soil in place. This mainly applies to terrain with minor slopes, where these walls serve as a required barrier to stop soil from moving forward during a landslide. Due to this, a retaining wall is a requirement for your landscape’s safety, assuring both your safety and the safety of your home.

Preventing Erosion And Improving Drainage

All landscape will eventually experience erosion, whether it be brought on by wind or water. Because of this, retaining walls are even more crucial, particularly if your landscape lacks a lot of trees and bushes to keep the soil in place. Retaining walls aid in minimizing sharper gradients, which not only maintain the soil but also aid in lowering surface runoff. This slows down the rate at which water flows over the surface, which lessens erosion.

Retaining walls accomplish all of this while also offering efficient flood control through water drainage designed to reduce floods. To add additional safeguards for appropriate drainage and water control, channels and drainage pipes can be incorporated into the construction. Finally, by terracing the area around the retaining wall, which allows water to percolate into the soil rather than run off the surface, the gradient is also reduced.

Aesthetics

Depending on their height and the type of material they are made of, retaining walls can prove to be durable and beautiful constructions. If constructed at the proper height, a retaining wall can also serve as a seating wall, increasing its usefulness. Your retaining wall may blend in seamlessly with other features in your yard thanks to the vast range of materials that are available, creating a stunning final product.

Gabion Walls

Gabion is a wire container that may hold any kind of inorganic substance including stone, concrete pieces, brick and more. The word is taken from the Italian word for “cage.” They are adaptable, permeable structures that are effective in preventing shorelines from eroding. In landscaping, gabion walls can be utilized as seating walls, accent walls, retaining walls, aesthetic site walls, and more.

Types of Gabions

There are numerous varieties of gabions. The typical types of wire mesh are gabion walls, gabion baskets, gabion beds, gabion sacks, and gabion wire mesh due to its malleability and versatility.

Gabion Basket

These box-shaped wire mesh baskets, which come in different diameters, are mostly used in highway and railroad construction.

Gabion Mattresses

The gabions act as mattresses to prevent erosion. These are used in channel coating, go by the moniker of “reno mattresses,” and are shorter in height.

Gabion Sacks

The cylindrical sacks made of double-twisted hexagonal-woven wire mesh gabions and filled with a porous, flexible structure are known as gabion sacks.

Gabion Wire Mesh

This is widely used on roads and railroads to stabilize slopes and prevent rock and stone falls. Together with geogrid reinforcement, welded mesh or wire mesh gabions are also used in embankments.

Advantages of Gabion Walls

Erosion Control 

Gabion retaining walls slow the flow of wind and water to shield any weak spots in your landscape from damage.

Installation is Simple

Creating gabions is straightforward and easy to learn. As their weight keeps them down, they typically don’t need to be buried in the ground, and unless your wall height is over 3 feet, they usually don’t require specialist design or installation.

Cost-effectiveness 

The main appeal of this situation is the freedom to select the fill material; as a result, you can set your own price and use materials that are inexpensive or even free.

Eco-friendliness

By selecting your own fill, you may also choose to use recycled or locally sourced materials to cut down on transportation expenses! You can recycle broken concrete pieces, leftover backfill materials, stone that is already on your property, and more.

Permeability

Gabion walls are great at lowering wind and water flow without completely halting it and redirecting that torrential downpour somewhere else.

Longevity 

Gabions have a very long lifespan and only get stronger with time. The wall merely gets stronger as the fill material settles and the spaces are filled with silt, vegetation, and debris. They are completely unaffected as the earth changes during freeze cycles and can rise and fall.

Disadvantages of Gabion Walls

Unsuitable For Small Projects

Gabions are heavy and difficult to bend or shape due to their inflexible frameworks. They work well for making big, bold, straight lines but are poor choices for narrow spaces or curving walls.

Potential Animal Habitats

All kinds of burrowing animals find the gabion walls’ nooks and crevices to be attractive nesting sites. Having local wildlife share your area with you can be a benefit, but not everyone wants to introduce a new neighbor to their yard.

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