US Patent 7168884 Reinforced permeable paving structure

A paving structure (11) of the type having an upper wear layer (12) and an underlying sub-base layer (15) of rigid insoluble hard particulate material forming voids for the collection of water permeating through the permeable surface where layer (12) has an intermediate reinforcing grid (16) located at an intermediate level of the sub-base layer (15) such that it is covered by an upper part of the sub-base layer (15U) which is of a thickness not less than 1½ times the dimension of the largest particles in that part of the sub-base layer. A reinforcing grid (26) at the base of the sub-base layer between this and the sub grade (18) may also be provided.