The blog of Alvaro Boiero
"Live as if you were going to die tomorrow. Learn as if you were going to live forever" Mahatma Gandhi
The blog of Alvaro Boiero
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"Live as if you were going to die tomorrow. Learn as if you were going to live forever" Mahatma Gandhi
Retaining walls: classification and uses
In some civil projects, it is common that there are differences in elevation between sectors of the ground. Such differences can be solved by profiling a slope, with a certain inclination to ensure its stability; or by means of a vertical or quasi-vertical retaining structure, when there are physical space limitations. These latter structures are known as retaining walls, and are fundamental elements to ensure the functionality of many projects.
Content
What is a retaining wall?
In civil projects, a retaining wall is a rigid vertical or quasi-vertical structure, which serves as a transition between two sectors of land with different elevations, and whose function is to control the predominantly lateral movement of the soil. Some practical applications of retaining walls are:
- Railroad and highway projects where there are differences in elevation in the ground, and there is not enough right-of-way to profile a stable slope.
- Bridge abutments.
- Construction sites on sloping ground, where it is necessary to form a horizontal surface.
- Marine structures used for berthing ships at docks and harbors.
- Flood control structures.
- Unstable lands, where the retaining structure provides the necessary strength to prevent landslides
Figure 1 shows some illustrative photographs of these practical applications.
Figure 1 Retaining walls (Source: compiled from www.google.com).
The procedure to be followed in the design of retaining walls consists, as in the case of many other types of structures, in the successive repetition of two steps: 1) the tentative selection of the dimensions of the structure; and 2) the analysis of the stability of the structure against the forces that will request it. In case the analysis indicates that the structure is not satisfactory, the dimensions are altered and a new analysis is performed (Terzaghi, 1955).
Classification of retaining structures
Retaining structures can be grouped into two main branches: externally stabilized retaining systems (those that support earth thrusts by their own weight or stiffness), and internally stabilized systems (those that provide reinforcement to the ground to ensure stability). Figure 2 summarizes the main types of walls, according to O'Rourke & Jones (1990).
Figure 2 Classification of earth retaining structures (Source: adapted from O´Rourke & Jones, 1990).
Externally stabilized retaining systems
As already mentioned, externally stabilized retaining systems are those in which the load due to earth thrust is resisted by the self-weight and stiffness of the retaining structure. Basically, we are talking about gravity walls and in situ walls (gravity walls and in situ walls, as shown in Figure 2).
Figure 3 groups the gravity walls most commonly encountered in practice, while Figure 4 shows the in situ walls, including the main characteristics of each.
Figure 3 Gravity walls.
Figure 4 Walls built in situ.
Internally stabilized retaining systems
Internally stabilized retaining systems are those that provide reinforcement to the soil to stabilize it. This type of system was developed in the 1960s and can be grouped into two categories: reinforced soils and in-situ reinforcement.
Soil is a material that is strong in compression, but has virtually no tensile strength. Thus, the inclusion of reinforced tension members in the soil can significantly increase its strength. The result is a mechanically stabilized soil.
Usually, this type of solution includes the placement of panels, although the main stabilizing effect is provided by the elements working in tension, thus forming a type of retaining wall. Reinforced earth walls are the typical example of this type of wall. This type of structure employs galvanized steel strips attached to prestressed concrete panels, as shown in Figure 5
Other similar methods are also used for this type of structure. Reinforcing elements may consist of steel strips, geotextiles, or wire mesh. Panels can be made of prestressed concrete, concrete blocks, gabions, and other materials.
On the other hand, in-situ reinforced soils include reinforcement elements inserted into the soil mass, instead of being placed during the formation of the backfill, as in the case of reinforced earth walls.
An in-situ reinforced wall is the soil nailing wall, which consists of drilling quasi-horizontal holes into which reinforcing steel (typically rebar or rebar) is placed and then filled with grout. Sometimes the wall is covered with shotcrete, as shown in Figure 6.
This type of structure does not require excavation work, making it a very useful solution for projects where space is limited.
References
- Coduto, D. (2001) “Foundation Design: Principles and Practices”. Second Edition. Prentice Hall. New Jersey, USA.
- O´Rourke, T. & Jones, C. (1990) “Overview of Earth Retention Systems”. Proceeding Paper. Part of Design and Performance of Earth Retaining Structures. Ithaca, New York, USA.
