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.
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,