crazy paving 
noun [mass noun] British
Paving made of irregular pieces of flat stone: [as modifier]: a crazy-paving patio...
- He said the gang has been vandalising benches and smashing stones from crazy-paving walkways in the historic cemetery most nights from 5pm.
- A decision to grass over a popular crazy-paving pathway has been branded ‘beyond a joke’.
- I built the dividing walls and even laid crazy paving.