Underpinning is like giving a house or building new shoes. Just like how we need shoes to walk, buildings need a strong foundation to stand. Sometimes, over time the ground underneath a building can move or sink, which can make the foundation weaker and the building less stable.
Underpinning is the process of digging under the building's foundation and filling it back up with a stronger material. This can be done by putting in extra concrete or steel beams to hold up the building's weight. Imagine putting on a stronger pair of shoes that can support your weight better, now your feet won't hurt as much and you can walk better. Underpinning the foundation of a building is like giving it new stronger shoes so that it can be stable and safe for everyone inside.