A failure in the foundation leads to the failure of the structure built on it. As we always discuss, the foundation must be strong enough to withstand the applied loads.
However, foundation failure may not only be due to the failure of the foundation itself, but also to the failure of the soil or support upon which the foundation rests.
Foundation failure can be discussed in several topic areas. Let's look at failures based on foundation types.
There are essentially two types of foundations.
- Shallow foundations
- Deep foundations
First, let's talk about shallow foundation failures.
Foundation surface defects
In this article, we focus primarily on shallow foundations such as footings and rubble foundations.
A shallow foundation can fail for the following main reasons.
- Failure in the bearing capacity of the soil
- Foundation structural failure
- Fails for other reasons
Foundation failure due to soil failure
If used too much, the floor may fail. The designer must therefore be aware of the failure modes of the soil beneath the foundation.
Even if the bearing capacity of the soil is correctly assessed, foundation failure can occur if the applied load exceeds the bearing capacity of the soil.
The article, Failure of Shallow Foundations discusses the method of soil failure when loads are applied. It provides comprehensive guidance.
Foundation structural failure
The foundation may fail due to insufficient bearing capacity. There are different types of structural failures in shallow foundations.
- Punching rupture
The failure of the foundation is due to the insufficient bearing capacity of the members at the critical shear perimeter.
The figure below shows punching rupture.
The article written as Piercing Scissors For more information about this type of design, see Design. The article covers the design process of die cutting scissors in detail.
- Vertical line shear failure
Foundation failure along the edge of the column.
This type of failure occurs when the shear strength of the foundation exceeds the maximum shear strength of the concrete.
According to BS 8110 the vertical shear capacity is √f cu or 4N/mm 2 .
No reinforcement is provided for vertical line shear. When the shear stress limit is reached, the thickness of the foundation must be increased.
- Bending failure
Exceeding the flexural capacity of the section will result in flexural failure of the foundations or any type of shallow foundation.
Due to the increase in acting loads, design or planning errors can also lead to such failures.
Failures for other reasons
- Design basis with insufficient information
When carrying out structural planning, the ground conditions must be known.
The dimensioning of the foundation can be done based on the assumed bearing capacity, taking into account the surface conditions of the soil.
However, as we all know, there can be weak layers of soil underneath, causing the foundation to settle. Soil layers with organic material and compressibility can cause settlements when loaded.
Furthermore, assessment of soil conditions and bearing capacity should be carried out by an experienced geotechnical engineer. Therefore, the correct interpretation of geotechnical conditions is very important.
Incorrect design can lead to foundation failure.
Therefore, the planner must know exactly the terrain conditions.
- Corrosion of reinforcements
In the case of armor, corrections are made due to insufficient coverage of the armor.
In general, reinforcement coverage is maintained in the range of 40-100mm.
The need for reinforcement to cover this depends on the durability requirements of the foundation. The decision is made based on the exposure conditions to which the foundation will be exposed.
Additionally, the condition of groundwater must be checked to determine whether it contains harmful chemicals. When ions such as chloride and sulfate are present in groundwater, we must be very careful.
When selecting reinforcing coverage, all of the above factors must be taken into account.
The minimum cement content of concrete is also chosen based on durability requirements as it impacts the durability of the concrete .
Next article on How to choose the quality of concrete For more information, see the section “Quality of concrete in construction”.
Deep foundation failures
The following types of foundations are considered deep foundations
- Bored piles cast in place
- Precast driven piles
- Micropiles
Failure of this type of foundation can occur for several reasons. Let's discuss the construction of cast-in-place concrete bored piles.
Failure of drilled concrete piles/micropiles in situ
The error can have several reasons explained below.
- Inadequate rinsing
After excavating or drilling cores for the pile foundation, it is necessary to clear the space to be filled with concrete. This is called rinsing.
If the clearance is inadequate, there is a possibility that the concrete will mix with the soil and soil will accumulate in the embedment area. There may be a weak layer (soil) at the bottom of the battery that causes it to sink when loaded.
- constriction
Reducing the diameter of the pile and lack of care can cause the pile to fail under load.
We perform the Stack Integrity Test (PIT) to check the stack. Normally this type of problem in piles can be identified through this test. If someone does the test, we won't be able to identify the problem at the stake. The following types of defects may occur when gutting piles.
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- Failure due to insufficient structural capacity due to inadequate section
- Corrosion of the reinforcement if it is exposed during narrowing.
- Insufficient geotechnical capacity
The pile design takes into account the geotechnical and structural bearing capacity.
In general, geotechnical capacity is crucial compared to structural capacity.
If geotechnical assessment capability is not developed, the pile may fail or settle when loads are applied. This may be due to insufficient development of skin friction and end bearing.
We test layers to see if they can mobilize the workload. Tests must be carried out appropriately and correctly to avoid problems of this type.
The most common pile tests are static and dynamic load tests.
The article on Retaining Wall Defects could also be used for failures in other types of structures.
For more information, you can consult the following articles on pile foundations.
- Design and construction of foundations using driven piles
- Pile Foundations – Guide to Design, Construction and Testing
- Pile slab foundations
- Problems and solutions in the construction of pile foundations
- Stack Design (Things to Remember)
- Types of foundations (a detailed study)
