There is no intention here to provide a concise flow chart or menu driven routine which will provide the reader with a full specification for any given situation. Not that we are holding back or exercising caution, the fact is that pavement design is a very broad subject with more complexities and technical anomalies than many other areas of engineering design. However, we can usefully consider what we know to be the major issues, so here they are:
Number 1 is 'Site Category'
For the uninitiated, this is a term used in British Standards to define the level of vehicular loading a pavement must support.
British Standards form the most useful and robust guidance and you will come across references to BS7533 throughout.
The number and type of vehicles which a pavement must support is fundamental to the design choices we can make.
Number 2 is the type of paving element.
This can broadly be broken down into 3 categories:
- "Setts" are paving elements which are usually less than 150mm wide and are usually as deep as they are wide.
- "Shallow Setts" are paving elements which are less than 150mm wide and are less deep than they are wide. The performance requirements for natural stone setts is described in BS EN 1342
- "Slabs" and "Flags" are paving elements which have a width more than 150mm and more than 2 times their thickness.
The performance requirements for natural stone slabs is described in BS EN 1341
The performance requirements for precast concrete paving elements is described in BS EN 1338
Using modern and affordable technology shallow slabs can be mixed with setts in the same surface, even under heavy vehicular trafficking but there are limits to what is possible and some design imperatives which must be followed.
Number 3 is the type of surface construction, bound or unbound.
Bound construction means paving elements bedded and jointed using mortar.
Unbound mortar means paving elements bedded and jointed using only aggregate.
You might find that we suggest an unbound construction for some situations. After all, why pay for mortar if it's not needed?
Number 4 is the type of cleaning regime employed. Yes, this is really important.
Number 5 is the supporting base layer upon which the paving is bedded.
Number 6 is "Detailing" and the Devil really is in the Detail when designing pavements and carriageways.