What is a Kelly Bar used for?

The Kelly bar is primarily used in foundation drilling, particularly in the installation of piles. It is a specialized tool that allows for the drilling of deep holes into the ground, which is essential for setting foundations that can support structures. The Kelly bar works by providing a means to deliver the drill into the ground, and it operates by rotating and moving the drill string up and down.

In the context of the given choice, it is specifically mentioned that the Kelly bar is used to install PISA (Piles Installed with a Digger Derrick). The digger derrick is a type of crane that is capable of digging and lifting, making it suitable for this application. Therefore, the use of the Kelly bar in conjunction with a digger derrick fits perfectly within its functional design and application in construction.

Other choices in the question do not accurately represent the purpose of a Kelly bar. They pertain to different mechanisms or functions not associated with drilling or pile installation.