Although on the surface it may appear that the gabion concept is a simple one, they are in fact highly engineered systems where specific performance criteria must be adopted during the design phase to achieve the required outcome. Maccaferri have been instrumental in determining these parameters as well as developing design processes stemming from their comprehensive R & D programs. Instrumented full-scale gabion walls, compression, friction reduction, tensile, punch, pull-apart resistance and full-scale flume tests is just some of the documented R & D that Maccaferri has been involved in over the years. The findings of these tests are specific to Maccaferri manufactured products only and one must not assume that units manufactured by others will yield the same results.
When gabions and Reno Mattresses® (Reno Mattress® is a registered trademark that refers to Maccaferri units only; other suppliers refer to rock mattresses) are specified in project tender documents, there is a tendency for the ‘basic requirements’ of the systems to be referenced i.e. mesh aperture size, wire diameter and coating type. Whilst these characteristics are important, the mechanical properties and therefore long-term performance of the gabion and Reno Mattress® units are equally (if not more) important. Over the past 20 years, I have witnessed many times where units seemingly conforming to the ‘basic requirements’ do not comply with relevant national and international standards with respect to quality, performance, and methods of manufacture.
Below are photographs of a rejected rock mattress and gabion from a New South Wales site that would appear to conform to ‘basic specifications’ in that they are manufactured from 2.0mm Ø and 2.7mm Ø double twist wire mesh respectively but in no way, conform to any national or international standards and should never be accepted by a designer or client. A cheaper price didn’t deliver value in this instance.
Rock mattress end panels ‘twitched on’ (the base and end panel should be manufactured from one mesh panel
Loose connection between gabion side panel and base (this should be an engineered mechanical connection)
The side panels and internal diaphragms have been loosely “connected” with what looks like individual ties for the rock mattress and a length of loose lacing wire using single twists for the Gabion. This could very well result in panels pulling apart if there is any movement of the structure or during high flows (unless the contractor has used additional methods to connect the panels correctly and that means extra time and costs). International specifications state that panels must be mechanically connected with minimum connection strengths between panels and there is no way this would be achieved looking at this substandard workmanship. The contractor that attempted to install these units informed us that each unit had to be manipulated into shape on site to achieve the desired outcome. In addition to performance, aesthetics will also be compromised with these poor-quality units.
A product and system specification should avert risk. Rather than merely stating the ‘basic requirements’, a specification should reference long term durability and long-term performance. If a supplier cannot provide the required independent test procedures and results, independent certifications (BBA Certificate http://www.bbacerts.co.uk/(link is external)(link is external), ISO manufacturing certificates etc.) and is not able to provide examples of projects demonstrating long term durability in similar Australian atmospheric conditions and applications, then how can they be considered to avert risk?
We often come across this issue relating to geotextiles, geogrids, geosynthetic clay liners etc. where “similar or alternative” products are not approved because their performance could not be substantiated. Gabions and Reno Mattresses® should be treated in the same way if not more stringently as they are visible after installation and their performance/or lack of can be easily monitored.
Examples of comprehensive performance specifications that will avert risk:
Reno Mattresses to be “Maccaferri ” type manufactured according to EN 10223-3:2013 from double twisted, hexagonally woven wire mesh of nominal 60×80 mesh, with 2.4mm frame wire and 2.0mm mesh wire, complete with diaphragms at 1m centres. Diaphragms shall consist of two layers of mesh having the base of the Mattress, diaphragms and end panels manufactured from one continuous mesh panel. All wire is mild steel, Galmac coated (Zinc-Al5% alloy) to the requirements of EN 10244-2 (Table 2 – Class A) and heat bonded through extrusion with an additional 0.5mm heavy duty grey polymer coating. Reno Mattresses must have a valid British Board of Agrément (BBA) certificate for zinc-aluminium alloy & polymer woven mesh and be manufactured in an ISO 9001 certified facility. Results from testing to determine their thickness in relation to water velocities must be provided.
Gabions to be “Maccaferri” type manufactured according to EN 10223-3:2013 from double twisted, hexagonally woven wire mesh of nominal 80×100 mesh, with 3.4mm frame wire and 2.7mm mesh wire, complete with diaphragms at 1m centres. All components to be mechanically connected at the production facility with a minimum panel to panel connection strength of 23kN/m; test done as per ASTM A975. The nominal tensile strength of the wire mesh shall be 50kN/m; test done as per EN 10223-3:2013. The punch strength of the wire mesh shall be 67kN; test done as per UNI 11437. All wire is mild steel, Galmac coated (Zinc-Al5% alloy) to the requirements of EN 10244-2 (Table 2 – Class A) and heat bonded through extrusion with an additional 0.5mm heavy duty grey polymer coating. Gabions must have a valid British Board of Agrément (BBA) certificate for zinc-aluminium alloy & polymer woven mesh and be manufactured in an ISO 9001 certified facility.
HOLD POINT – If gabions and rock mattresses other than those manufactured by Maccaferri are proposed by the contractor, conformance must be verified by the designer using the alternative manufacturers test results and certificates referenced in the above specifications.
When gabions and rock mattresses supplied by others do not perform as intended (and we unfortunately have many examples of this in Australia), it is gabions perse that get a bad name, not a specific suppliers unit. Whilst Geofabrics value competition in the market place, we believe that the market needs to be well informed. When a supplier offers a cheaper sub-standard product, and merely states (without documented evidence) that it is equivalent to Maccaferri, then we recommend that the relevant documentation and test data be requested so that an informed comparison can be made.