Welcome to the Vibrary!

This is a compactor and it compacts the soil to provide a solid foundation on which to build. It's vital to have the ground as packed down as possible, no holes or pockets that could later shift and cause improper settling, or in the worst case, cracking and compromise the integrity of the foundation.
The compactor also makes the entire building vibrate: the floor, walls, shelves, computers, patrons and librarians. Driving it must be much worse, though, and I'm sure all the earthworms for miles have headaches.