| Mechanical weathering is the gradual process of decay on artificially-created objects and infrastructure, due to the movement of the earth, plant growth, and other non-weather-related events.
A tree whose roots grow under a sidewalk, pushing up and eventually cracking it, contributes to the mechanical weathering of that sidewalk. Similarly, ivy deteriorates and can destroy a wall or building, if left to run amok.
Old pathways where many people have walked eventually sink down in the center, due to the millions of feet which have traveled them over the centuries. Freeways develop ruts from the trucks which traverse them; high freight traffic means this usually only takes decades. | 
