Detailing

The Devil is in the Detail, so they say. Well, he certainly has his fingers into pavement design if you're not careful.

What are some of the 'details' which commonly cause problems if they are not properly addressed?

Movement joints

This is where the Landscape Architect, the Civil Engineer and the Structural Engineer might often disagree. It is certainly a subject where careful thought should over-rule standard design manual edicts.

There might be requirements for movement joints in a concrete road base or concrete podium deck structure. Of these two the podium deck rarely poses problems as what movement joints there are have been dictated by reasons other than shrinkage of the concrete. The need or otherwise for movement joints in a concrete roadbase is a frequent cause of disagreement even among engineers.

In one circumstance an engineer might not ask for movement joints in a concrete base which is 40 metres in length.
Some smaller projects have been aesthetically ruined by movement joints criss-crossing at 6-metre intervals.

Firstly it should be carefully considered to what extent movement joints are required in a concrete base, both for shrinkage in curing and thermal movement in service, careful design can reduce or eliminate the requirement for movement joints.

Movement joints in a surface course of setts represents a highly undesirable risk of failure and special measures must be taken if some movement must be provided for.

Movement joints in a surface course of paving flags or slabs do not represent any risk and need not be excessively wide, they might also be disguised if care is taken.

Edge restraint

The setts at the perimeter of a pavement are vulnerable to structural failure and special measures should be taken. Setts are relatively small in relation to the forces they are subjected to by vehicular trafficking, even setts as large as 150 mm rely upon their neighbours on all sides to prevent them from tipping sideways when subjected to heavy lateral loading. Individual setts bounded by neighbouring setts are highly resistant to stress but those at and near the perimeter of an area are in danger unless a suitably strong and stiff edge restraint is provided.

Sadly, adequate edge restraint is not always provided and failure in this situation is widespread.

We produce Technical Notes from time to time, intended to address particular situations. These are added to and updated, as time permits, and we appreciate the regular input we receive from interested industry professionals. In this way, we hope to continue to develop a productive dialogue within the industry and to share knowledge.