What is Foundation Settlement? – Types & Causes

Different types of foundations will be selected based on the soil density, bearing capacity to make the structure strong and durable.

However, a small amount of displacement will happen during construction or after the construction of the structure by the load occurrence regardless of the foundation. 

What is meant by settlement of foundation?

Imagine you try to stand on wet soil. After some time, you could see your footprints on the ground. How? Because you applied a force on the soil, which makes it compress and displaced it, making a dent.

The same applies to buildings. A vertical displacement that happens on the structure when the load occurs is called settlement of the foundation. The foundation settlement is measured in mm.

Types of foundation settlement

The foundation settlements have been classified as below.

• Uniform Settlement – The whole structure settled at a uniform rate without cracks is called uniform settlement. It happens when the structure is located at the same layer of soil up to foundation depth, and it does not have any major impact on the structure. 
• Tipping Settlement – When one portion of the structure settles down to a certain depth is called tipping settlement. It may lead to cracks in the construction and induce the collapse of the entire structure. 
• Different settlement – The differential settlement happens when the structure is built on soil, containing different layers. Different structure portions may settle down differently, and cracks appear on different elements of the structure, which leads to a collapse of the entire structure.

Total settlement of a foundation

The total vertical displacement (the combination of all settlement) happens at the foundation due to load occurrence is called a total settlement of the foundation.

The specification and calculation of foundation settlement have been mentioned in IS code 8009 Part 1 and Part 2.

It is classified as,

• Immediate settlement happens immediately after a particular stage of construction work on coarse-grained soil due to load occurrence.
• Primary settlement – Primary settlement happens slowly at the period of 2 to 5 years after completion of construction activity.
• Secondary settlement – It happens in the total life span of the structure and creates severe effects. 

Causes of foundation settlement

The structure may settle down due to the following reasons,

• Due to the leakage of sewage water.
• Inadequate bearing capacity of the soil.
• Improper compaction or consolidation.
• More vegetation root depth near to the foundation. 
• External vibration occurrence near to the foundation.
• When major excavation happens near to the foundation.
• The structure will settle down in case of seepage occurrence. 
• When the structural elements are built at different depths of foundation. 
• When the foundation is not constructed at a minimum depth of foundation. 
• When the structure was built on loose soil without proper type of foundation. 

Prevention

• Provide a minimum depth of foundation.
• Remove any tree roots passing beneath the foundation.
• Ensure proper compaction has been done on foundation depth.
• The right type of foundation has to be chosen for construction.
• Proper soil investigation has to be done before starting the construction work.
• Design the foundation which can accommodate massive load occurrence on the structure.

Permissible settlement of the foundation

The foundation settlement for different construction works has been mentioned below.

Happy Learning 🙂