Other Considerations

From a pavement point of view, it is desirable to keep the aggregates in the pavement as dry as reasonably possible — so as to promote strength, stiffness and resistance to deterioration (see Chapters 8-10) — but the pervious pavement concept is directly in opposition to the general principle. Therefore other strategies have to be taken to make sure that the pavement provides sufficient strength, stiffness and durability for traffic loading. Normally this requires particular attention to aggregate quality. While, typically, aggregates to a 4-40 mm grading range, or similar, are required to ensure a suitable pore space for water storage, their requirement for durability may be higher than conventionally. There are greater stresses on particles conse­quent on them having an open structure with fewer contact points (see Chapter 9, Section 9.2). Also, more load spreading should be achieved, if possible, in the over­lying pavements. Furthermore the design must allow for softening of the subgrade caused by the water stored in the pavement. Some design information is given in Woods Ballard & Kellagher, (2007) with more information given in Pratt et al (2002) and, for block pavements, Interpave (2005).