Passive linear protection via stone blocks
Stone screens are recommended to fight against the spread of smaller instabilities This passive solution (which does not prevent falling elements) is adopted by default by active solutions at the source of the problem and where there is a risk in a straight line Essentially, this type of protection is found by the roadside
ETAG 027 norm for stone blocks
In the context of the new European norms concerning stone blocks (norm ETAG 027), it is essential to scale the protection to be implemented in advance. Calculation of force of impact is realized according to the level of potential instability (MEL – Maximum Energy Level), and with this the trajectories and heights which determine the stone screen’s capacity.
- For impact energy below 100 kJ (MEL), a screen in accordance with ETAG norm 027 is not necessary. Here the French standard NFP 95-308 can be applied to class 1 screens (25kJ) or 2 (50 kJ), and full-scale testing of the screen is not necessary, in contrast to screens at higher impact levels.
- Conversely, for impact energies greater than or equal to 100 kJ (MEL), a screen according to ETAG is recorded, and full-scale testing of the screen is necessary, in contrast to screens at lower impact levels.
In addition, frequent inspection is necessary to guarantee its capacity to absorb possible impacts.
Finally, advance geotechnical studies are less important for the design of this type of work. The cost remains relatively friendly to the client. The effectiveness of this solution is limited by the source of the problems not being addressed. At the same time, its maintenance can be increased to supply a reasonable level of protection when the upper areas produce large amounts of material which accumulate at the foot of the screens.