How to read a rockfall barrier specification — from ETAG 027 to EAD 340059

Two documents, one transition

Flexible rockfall protection kits have been certified in Europe since 2008 with a single full-scale impact test. The first document was ETAG 027, the EOTA guideline published in 2008 and updated in 2013. When the Construction Products Regulation (CPR 305/2011) came into force, guidelines were replaced by European Assessment Documents. For barriers that document is EAD 340059-00-0106 (formerly ETAG 027), published in the Official Journal of the European Union in 2018.

For the specifier the consequence is simple. A new system receives its European Technical Assessment (ETA) under EAD 340059. Certificates issued under ETAG 027 remain valid, and manufacturers still quote a 2015 ETA in their Declaration of Performance as "ETAG 027 (EAD 340059-00-0106)". Writing only "conforming to ETAG 027" refers to a guideline that is no longer in force. The correct reference is: "CE-marked system with an ETA under EAD 340059-00-0106 (formerly ETAG 027)".

The test method is the same in both documents. What changed is the legal basis and the fact that a Declaration of Performance (DoP) became mandatory.

MEL and SEL: two numbers, two questions

Every certified barrier carries two energy values.

MEL — Maximum Energy Level. The largest energy the system stops in a single impact. In the test the block is released onto the central module of the net at a mean speed of at least 25 m/s over the last metre before contact; the system must stop it. Maximum elongation and residual height are measured in this test.

SEL — Service Energy Level. The guideline requires MEL to be at least three times SEL; the SEL values in the class table follow from that ratio. In the test the system takes two consecutive SEL impacts. After the first impact, measured with the block still in the net, the residual height must be at least 70 % of the nominal height; the block must not touch the ground and no mesh opening may open to more than twice its initial size. No repair is allowed between the two impacts. The system must stop the second block as well.

The two numbers answer two different questions. MEL answers "what happens if the worst block arrives". SEL answers "does the barrier stay in service while ordinary blocks come and go". A specification that gives only MEL has not asked the second question.

Energy classes

Classes run from 0 to 8 (ETAG 027, Table 2). The certified energy may not be below the table value for its class; the SEL column follows from the rule MEL ≥ 3 × SEL.

Class 0 has no SEL test and no SEL value. Class 8 is open-ended: every system tested above 4,500 kJ is declared in class 8 and its real SEL and MEL are written separately in the certificate. A barrier certified at 8,000 kJ is therefore declared as class 8, MEL 8,000 kJ, SEL above 2,667 kJ. This is why a specification states the required MEL and SEL, not a class number. The class itself is chosen from the design block mass, the impact speed from trajectory analysis and a safety factor — see How to choose the energy class of a rockfall barrier.

Height, elongation and clearance

The energy class alone is not enough. Three geometric values also belong in the specification.

Nominal height is the smallest distance, measured perpendicular to the reference slope, between the line joining the post bases and the upper support rope, measured before impact. The manufacturer's "commercial height" adds an allowance to it; the specification states the nominal height. It is chosen from the bounce height measured on site: trajectory analysis gives the 95th-percentile value.

Maximum elongation is the distance the net travels downslope in the MEL impact. The clearance to the protected asset follows from this number. The Declaration of Performance lists class, MEL, SEL and the residual height category; maximum elongation, the measured residual height, the forces on the foundations and the installation manual are in the ETA and the manufacturer's documents. Ask for the ETA itself and the installation manual with the tender.

Residual height is the smallest distance between the lower and upper ropes, perpendicular to the slope, measured after the test with the block still in the net. For MEL it is declared as a category: A — 50 % and above, B — between 30 % and 50 %, C — 30 % or less, or rupture of a support rope. A category A system remains largely in service even after a design impact. Above roads and other places where a second block is expected, the category is written into the specification.

The word "equivalent"

The most expensive word in a specification is "equivalent". A flexible barrier is tested as a kit: net, ropes, brake elements, posts and connections together. The performance of a combination that was never tested is unknown. One manufacturer's net with another manufacturer's brake element is not "equivalent"; unless the test is repeated, that number does not exist.

Two sentences therefore belong in the file. Components shall belong to one manufacturer and form part of the tested system. The ETA, the Declaration of Performance and the installation manual shall be submitted with the offer.

Eight clauses for the specification

1. Certification basis: CE-marked system with an ETA under EAD 340059-00-0106.
2. Energy: MEL at least [kJ], SEL at least [kJ]; both values from the class pair in the certificate.
3. Nominal height at least [m], based on bounce height and trajectory analysis.
4. Residual height after the first SEL impact at least 70 % of nominal; category [A/B/C] after MEL.
5. Maximum elongation [m]; clearance to the protected asset set accordingly.
6. Corrosion protection: hot-dip galvanizing to EN ISO 1461 on posts and steel parts; zinc or zinc-aluminium coating to EN 10244-2 on wire, mesh and ropes, class stated.
7. Anchors: type and length from the design; execution to EN 1537 or EN 14490 according to anchor type; one pull-out test per [n] anchors, with a signed record — see Anchor and rock bolt pull-out testing on site.
8. Acceptance: as-built report with photographs and coordinates; annual inspection checklist and post-event procedure handed over — see Rockfall barrier inspection and maintenance: checklist.

One step further

The Austrian standard ONR 24810 ties the certificate to a design code. It defines three consequence classes according to the importance of the protected asset and applies partial factors to energy: the 99th-percentile energy from trajectory analysis is multiplied by 1.00, 1.05 or 1.15 depending on the consequence class, and on the resistance side the barrier's MEL is divided by the same factor. A barrier above a highway is therefore selected one class higher than a barrier above open ground. Oman has no national rockfall code; when the client asks why class 6 was chosen instead of 5, this is where the answer comes from.