In New Zealand road safety barrier hardware used on the State highway network is subject to compliance testing to ensure that it performs satisfactorily for typical crash conditions. The hardware is accepted by the New Zealand Transport Agency as meeting the tested conditions only, and details of the accepted system will include properties such as dimensions and material, and specific installation placement and geometry.
The developer of the system, in conjunction with the supplier, will have written the product and installation manual using the tested conditions. The Transport Agency will have reviewed and accepted this manual as part of the product acceptance process. Any acceptable variations to the conditions used in testing will be documented in that manual.
An example of this is the concrete footing depth for posts used in Wire Rope Safety Barrier systems. The standard option for post footings for Armorwire Cable Barrier is 300mm diameter by 750mm deep hole filled with 25 MPa concrete. For the Brifen Cable Barrier system the post foundation size is 250mm dia x 750mm deep hole filled with 25 MPa concrete. These options are for footings installed in an AASHTO Standard Soil only - this being the standard soil used in testing. AASHTO Standard Soil may not be able to be achieved in medians or edge fills for either composition or compaction and this will result in the installation not performing as tested and accepted. As a result, in an impact, the system deflections will be much greater and the footings may be damaged and require replacement. For those locations where soil strength is an issue, the Armorwire and Brifen systems have accepted alternative designs ranging in depth from 400mm to 850mm, or more, depending on the strength of the soil on site. On site soil testing will be required to ensure the correct post footing depth is selected. The installer and the engineer need to ensure that acceptable foundations are achieved.
Any unaccepted variation in the product or installation detail may result in the system no longer meeting the original Transport Agency acceptance and potentially posing a risk to an impacting vehicle. This can raise significant liability issues for the contractor, consultant and unacceptable risk for the road controlling authority.
The system installer should ensure that they are fully informed of the installation requirements for a system compliant with the Transport Agency acceptance. Any potential variation in set out or material modifications should be escalated to the client’s engineer for review and acceptance. For proprietary systems the engineer must seek advice from the supplier in considering the variation. When a significant variation is required this may require the client’s direct involvement and acceptance as non-accepted variations run the risk of the client rejecting the installation as not fit for purpose. To remedy the installation after completion can be very expensive, especially when significant rework is required.