Retaining wall (a detailed study)

June 5, 2024 Roberto Magalhães

This article explains the types of retaining walls and their behavior. Various classifications of support systems are also discussed.

Why do we need a retaining wall?

Any structure used to hold earth in place is generally called a retaining wall. There are other types of support structures that support materials such as stones, sand, etc.

The design of support structures is not the same for all types of structures. It depends on the structural behavior and forces acting on a retaining wall .

Types of retaining walls

Gravity (masonry, stone, concrete, etc.)
Semigravity
Cantilever/supported
Counter pillars/support pillars
diaphragm wall
Anchored
Sheet piling wall (sheet piling, perforated wall, secant, tangent)

Let's discuss each type in detail.

Gravity Retaining Wall

As the name suggests, the structure supports the load through gravity. In other words, the weight of the structure itself acts as a counterweight to absorb the applied tipping moment.

Different materials are used to build support structures. Masonry and stones were previously used for construction.

However, with the development of the construction industry and the introduction of concrete, concrete gravity retaining walls have become increasingly popular.

Generally, gravity support structures are constructed as solid concrete structures. However, in some situations nominal reinforcement is provided to prevent thermal cracking.

Gravitational support structures are mainly used in the construction of hydraulic structures.

Semi-gravitational support structures

This is a further development of gravitational structures. In a gravity structure we generally do not provide any Reinforced Steel to carry the load.

With a semi-gravitational construction, we provide a certain amount of reinforcement to absorb the resulting tensile stresses on the surface, where the pressure of the earth acts.

When greater forces are applied and the width of the retaining wall cannot be increased, reinforcement with a modified base is provided to maintain stability.

Cantilever retaining wall Retaining wall

Cantilever walls are the most common type of construction we have seen in construction. In general, they are reinforced concrete structures.

This type is most effective when space is limited. We can reduce the thickness of the wall with the reinforcements provided for the wall and foundation.

The actual retaining wall is also the same self-supporting retaining wall. The only difference is that support is provided at the top level to control the subsequent deflection at the top.

Unlike a cantilever retaining wall, a supported cantilever wall is more stable.

retaining wall and retaining wall

Both types of retaining walls are used when the height of all retaining walls increases.

As the height of the free cantilever wall increases, the dimensions and reinforcements need to be increased. With significantly higher wall heights, this is no longer economical.

For example, at heights of 7 to 15 m, we may consider installing additional reinforcements to reduce loads on the main wall.

Most importantly, the construction of buttresses and retaining walls does not lead to an improvement in wall stability. Only the increase in self-weight through the diagonal walls contributes to increasing resistance to tipping.

Retaining wall with strong counter

The name indicates the arrangement of the reinforcing walls. There are counter supports in the wall that improve the rigidity of the wall.

Bracing walls are placed where earth pressure applies to this type of wall.

The retaining wall is not as effective as retaining walls with buttresses because the retaining wall is under tension. If the element is in tension, we must provide sufficient reinforcement to support the loads.

Support pillars can have different shapes. It is not always necessary to take into account the total height of the wall and the width of the foundation. There may be smaller supports, which effectively reduce the wall's bending and shearing forces.

Retaining wall with supporting pillars

Braced walls provide similar support to the main wall in reducing bending and shear forces.

However, compared to retaining walls, it is more efficient because in this type the concrete is subject to compression forces. Concrete can absorb compressive forces more efficiently.

Reinforcement walls are located outside. If there is space outside to build the reinforcing walls, this option is more economical.

diaphragm wall

This type of wall is a novelty in the construction industry. The construction method is most similar to in situ concrete bored piles.

Diaphragm walls are constructed as a replacement for retaining walls made of sheet piles, secant pile walls, etc. The same wall can be used as a basement wall after construction.

Diaphragm walls are becoming more and more popular nowadays in the construction of deep basements.

Diaphragm walls can be constructed as independent walls that can only support lateral loads. For deeper basement structures, diaphragm walls can be constructed as anchored or supported walls.

Anchored walls

For taller retaining walls, one of the most commonly used methods is to cap the side of the retaining wall to maintain its stability.

As the wall height increases, we need to increase the wall thickness. If side boundaries are provided at regular intervals, we can reduce the cost of the wall.

The application of lateral limits can be observed on several occasions.

Make sure the concrete walls are enclosed on the sides.
Provides lateral limits for sheet piling walls

Generally, anchorage termination is carried out beyond the geological fault, ensuring the required safety factor.

Pile retaining walls

Pile foundation methods are often used to protect soil in deep underground structures.

Although building the support system takes time, the stake method is more reliable. Furthermore, it can bear a comparatively greater load compared to a sheet piling wall.

There are different types of sheet piles.

Sheet pile walls
Bored pile walls
Sectional pile walls
Tangential pile wall

Pile retaining walls are also designed as anchor walls.

In addition to the types of retaining walls mentioned above, there are other methods of anchoring them to the earth.

The most common systems available are explained below.

Soil Nail Walls
Floor reinforcement
Gabion mesh
Mechanically stabilized earth retaining walls
Nativity Wall

Let's discuss each category in detail.

Soil nail wall

It is a type of earth retention system most commonly used to stabilize slopes. Prevents lateral movement of the earth more effectively.

This process is most common in road construction.

The steel road, anchored in the deep layer of earth, is designed in a regular grid according to the project requirements. These points are interconnected by reinforced concrete beams.