Building with granite: drainage systems in outdoor pavements
The durability of the pavements depends on a well executed drainage. The accumulation of water, both on the surface and inside a pavement, is a matter that should be avoided at all costs.
The calculation of drainage needs must contemplate not only rainfall data from the area, but also the work of flushing, cleaning and maintenance of the road.
In the drainage, the following elements are involved that must be considered in a timely manner: the surface slope of the pavement, the slope of the drainage pipes, as well as the lids and grids of the manholes, gutters and drains.
The tiled pavements must develop the water evacuation by surface runoff, until reaching the concave pavings, gutters or drainage pipes arranged for this purpose and that in turn connect with the general drainage network of the area through sewers or drains.
To do this, the surface of the pavement must have the appropriate slopes both longitudinally and transversally.
The transversal slopes must reach a value between 1.5% and 3%, depending on the rainfall characteristics of the area and the surface roughness of the stone. Likewise, they have to be formed from the natural esplanade, so that the structural base and the base of support and adherence maintain their uniform calculated thickness.
Logically, the topography of the natural terrain completely conditions the design of the drainage system, being able to develop, in this sense, different alternatives.
The longitudinal slope is almost always forced by the original topography of the natural terrain and does not usually need drainage elements, as it happens in the transversal slopes, except when strong slopes are combined with long routes.
Slope of drainage pipes
In internal drainage systems, the slopes of the pipes or gutters must reach at least 1.5%.
Lids and grids of the gutters, manholes and drains
For the design of this type of units, it is necessary to take into account the amount of circulatory traffic loads. For this, it is necessary to take into account the adequate thickness that allows supporting these loads, in accordance with the UNE-EN 124 Standard.
Regarding the gutters there are two types:
- Of uniform depth along its entire length: they are the most common and entrust the efficiency of the drainage to the support slope.
- Its section increases proportionally to its length: The gutter itself has a design that forms its own slope at the expense of increasing depth. They should be used in flat areas, where the slope of the terrain is not sufficient and it has a reduced extension.
The condition of the drainage network is a critical point in the maintenance plan for outdoor pavements. This must be inspected and cleaned with the usual mechanical or manual means, since only with a drainage network in good condition it is possible to guarantee the conservation of the outdoor pavement.
EVA PORTAS FERNANDEZ
AREA OF TECHNICAL CONSULTANCY
(TECHNOLOGICAL FOUNDATION CENTRE FOR GRANITE OF GALICIA)