Measure your paving

The first thing is to define whether our natural stone paving will be made up of paving stones or cobblestones, as the calculation methodology is different in each case.

In this post we will focus on how to calculate the thickness of paving stones, although to do this we must firstly check whether their use is suitable depending on the amount and intensity of traffic to which they will be subject (issue addressed in another entry: “exterior pavements with granite”). We must also not forget the importance of the quality of the area of level ground on which it will be supported.

The thickness of the paving stones depends on the:

Calculation of the thickness of a paving stone is made by considering two types of stresses: bending forces and the impact of hard bodies. It is advisable to choose the greatest thickness obtained from both options:

A) Thickness of the paving stones considering bending forces

This is calculated according to the expression

 

 

 

where,
P: Traffic load (kN). See table 1.
L: Length of the paving stone (mm)
F: Combined factor of security and putting. See table 2.
W: Width of the paving stone (mm)
ViE: Lower expected value of the resistance to bending (MPa). This value is obtained from a laboratory test on the chosen stone according to UNE-EN standard 12372.

Should you wish to change the obtained thickness for a certain project once the stone has been chosen, the only variables that we could amend to recalculate the thickness would be the length and width of the paving stone.

B) Thickness of the paving stones considering impact by hard bodies

The thickness of the paving stone must be capable of absorbing shock energy due to impact. Thus, depending on the use of the land, a minimum shock energy is recommended (table 3). This value is known for each variety of stone and the chosen dimensions according to the test described in UNE-EN standard 14158. Determination of shock energy due to impact, which consists of dropping a 1kg steel ball several times on to a paving stone placed on a sand bed, increasing the height until it breaks.

Sources:
 Guide for the design, construction and maintenance of exterior natural stone pavements. Fernando López González-Mesones (coord.), 2012.
 UNE-EN 12372: 2007. Determination of the resistance to bending under a concentrated load.
 UNE-EN 14158: 2004. Determination of shock energy due to impact.

Nuria Sánchez Delgado
Doctor in Geology
TECHNOLOGICAL CENTRE OF GRANITE IN GALICIA