This article explains various forces acting on a retaining wall and their influence on the behavior of the retaining wall. Depending on the type of construction, the forces acting on retaining walls vary.
For example, active pressure and resting pressure can be taken into account. Based on the structural behavior, the forces to be taken into account during the design are evaluated.
Let's go directly to the forces acting on retaining walls.
Type of force acting on a retaining wall
We build a retaining wall to retain water, soil, solid waste or other materials in an unstable dam.
Depending on the type of material to be retained as per the project requirements, there are different types of retaining walls such as concrete retaining walls, gabion walls, etc.
However, the application method and type of loads are similar for most types of retaining walls.
Lateral earth pressure
Depending on the behavior of the retaining wall, lateral loads are applied in three ways.
- Active earth pressure
Force exerted by the floor on the wall when the wall is free to deflect. In other words, for simplicity, let's say the floor moves toward the wall.
Active pressure is calculated using the following equation.
P A = k A γh; k A – active pressure coefficient = (1-sinΦ) / 1+sinΦ), γ – soil density and h – wall height
- Passive earth pressure
Pressure Earth pressure occurs when the wall presses against the ground. Here, for simplicity, we say that the wall moves towards the floor.
Passive earth pressure can be calculated using the following equation.
P P = k P γh; k P – passive pressure coefficient = (1+sinΦ) / 1-sinΦ), γ – soil density and h – wall height
- Resting pressure or resting state
This is a special case and the pressure varies between active pressure and passive pressure.
When we talk about rest, we assume that the structure is not moving. Therefore, the pressure exerted on the wall is greater than the active pressure.
The inactive state is taken into account in special situations and the behavior of the structure can also cause the inactive state.
For example, we design a rigid structure as a retaining wall, and if it does not deform when subjected to ground pressure (active pressure), the pressure will increase and the structure can reach the rest state.
Furthermore, during the design we took into account the state of rest, when the structure requires a minimum deflection. For example, if we build a cantilever retaining wall where we need to limit upward deflection, it must be designed for rest.
So we have a comparatively rigid structure that can limit deflection when force is applied.
The pressure exerted at rest can be calculated using the following equations.
P 0 = k 0 γh; k 0 – Resting pressure coefficient = (1- sinΦ), γ – soil density and h – wall height
The article Coefficient of Lateral Earth Pressure More information can be found at
surcharges
The surcharge is a pressure load on the floor maintained by the wall.
It may be some form of line load or evenly distributed load.
Correct assessment of the surcharge is very important in planning. For example, if there are structures close to the retaining wall, the correct pressure must be taken into consideration in the planning.
An incorrect estimate can lead to retaining wall failure .
Water pressure
It is very important to know the forces that act on a retaining wall due to pore water pressure.
Incorrect assessment of water pressure can lead to failures, as described in the article Retaining wall failure .
Water pressure significantly changes the safety factor.
Therefore, special attention must be paid to water pressure during construction and, whenever possible, adequate drainage must be provided.
Axial forces act on the retaining wall
If the retaining wall is supported by other structures, we must consider their influence on the structure.
Axial load failures are not common in retaining walls because a significant cross-section is required to accommodate vertical loads.
Retaining walls and their foundations in some structures are sometimes considered columnar foundations. In such a situation, a correct design must be made for the ultimate limit state and the serviceability limit state.
wind loads
Typically wind loads are not that critical for retaining walls.
However, if there are other structures on the independent retaining wall, this may affect its stability.
For example, high walls built on top of the wall can have some effect. But this may not be so critical.
Seismic loads
Seismic forces acting on a retaining wall have a significant impact on the stability of the retaining wall.
We calculate the earth pressure coefficient (active pressure, passive pressure, rest pressure) and then estimate the applied load.
The guidance was published as Retaining walls and flooring. IN US Army Corps 1110-2-2502 , find more information about the equations that can be used to calculate earth pressure coefficients.
The article appeared as Seismic Pressure Coefficient Reference can also be made to the excerpt from the guideline mentioned above.
Impact loads such as accidental loads, blast loads, etc.
Impact loads are not as common in retaining walls. They can only occur very rarely.
Furthermore, there is a lower probability of these loads acting against stability than if there was a high probability of pressure being applied to the exposed surface, creating a restoring moment.
However, retaining walls can be damaged by such loads.
Other powers
If retaining walls are built on top of another structure and this is considered the foundation of the wall, additional stresses may occur in the wall.
For example, if we build the retaining wall on the slab foundation as a basement wall, when loads are applied to the slab foundation, some of the stress will be transferred to the wall due to the stiffness of the wall.
The out-of-plane bending action of the slab foundation is transferred to the wall as in-plane stress. Due to the high stiffness in the in-plane direction, there is a significant increase in wall stress.
This must be checked during construction.
