Retaining walls - what is a retaining wall?

1. What is a retaining wall?

A retaining wall is a structure whose primary purpose is to support an embankment or slope. It helps prevent the collapse, depletion or deterioration of soil or engineering fill, i.e. landslides, and also creates level areas on sloping sites. In addition to this primary role, a retaining wall (either solid or hollow) also has an aesthetic role since it can be a decorative element that will break up the monotony of the terrain.

2. Types of retaining structures

Retaining walls or structures can be divided into two basic groups - mechanically stabilised earth structures and embedded ones.

2.1. Mechanically stabilised earth structures

This group of structures, also known as reinforced soil structures, includes (solid) stone retaining walls, stone structures, various forms and types of reinforced concrete walls (or similar materials), concrete or wooden crib walls, and gabion walls.

2.2. Embedded retaining structures

This group includes bored reinforced concrete piles, with the piles either interlocking (secant) or installed next to one another (contiguous), diaphragm walls and panels, and reinforced concrete or steel king post (Berlin) walls with horizontal wooden or concrete lagging in between.

2.3. Calculating the dimensions of retaining structures

Mechanically stabilised earth structures use self-weight to transfer the destabilising earth forces acting behind it to the substrate. They can be rigid or flexible with elements made of different building materials.

When determining the dimensions of retaining walls, above all, the actions of the primary physical forces such as the pressure of the soil and the retaining structures own weight must be taken into account. In addition to these, other stresses impact mechanically stabilised retaining structures.

When performing analyses and static load calculations, the bearing capacity, toppling/overturning, the position, the impact of forces on the bottom of the foundations, possible sliding under the foundations, and groundwater must all be taken into account, as well as the dimensions of the critical points of the wall itself.

3. Building a retaining wall

When building a retaining wall, the pressure of the soil on the wall and the size of the foundations need to be considered, as well as the strength of reinforcement and the quality of the concrete mixture, i.e. the concrete grade, if it is a reinforced concrete structure.

A retaining wall does not necessarily have to be made of reinforced concrete. This type of wall can also be made from concrete or stone blocks. The main role of the retaining structure is to prevent soil erosion on steep terrain as well as to prevent water penetration from a higher to a lower level. The type of retaining wall used, whether it is solid or hollow, and what material it is constructed from will depend on the complexity and type of terrain.

Regardless of the existing state of the terrain, construction itself always begins with the excavation of a trench for the foundations. The footing trench is then filled with gravel, which must then be compacted thoroughly. Once this subbase has been prepared, wooden formwork is placed along with steel reinforcement and then concrete is poured. Reinforcement consists of steel bars connected together to form a rebar cage. When the concrete has been poured, the wall foundations are finished. The concrete must cure properly before building work can continue.

When the wall has been built, drainage pipes with filters need to be installed to remove atmospheric and groundwater.

3.1. Waterproofing a retaining wall

When building a retaining wall, waterproofing is often completely ignored. Without it, footing concrete is completely exposed to the impact of surface runoff and water running down the wall itself. In order to avoid various types of damage, it is crucial that waterproofing is installed correctly and at the very outset.

4. Price of a retaining wall

The price always depends on several factors – above all, the quantity, type, and quality of materials, the accessibility of the terrain, how the wall will be built, and the contractor.