Published: 30 April 2020 | Category: Technical advice note | Audience: Road traffic engineers & consultants
This note is to advise that there is an issue with the use of hollow bar anchors and soil nails as an anchorage method and, as a result, this methodology must not be used unless its suitability for anchoring structural works as designed is demonstrable. The new requirement for hollow bar anchors and soil nails applies from the date of this notice for Waka Kotahi NZ Transport Agency, and may be used by any other road controlling authority.
Hollow bar anchors and soil nails have been used to anchor structures on roading projects following acceptance through the Bridge Manual departures process. The use of hollow bars appears to be becoming the ‘go-to’ anchor and soil nail type. Since their accepted use in the difficult and demanding ground conditions of the Kaikōura project they have grown in popularity as an anchor and soil nailing method, but there are concerns about the durability of hollow bars over the design working life of the structure.
The processes and procedures outlined in this update must be followed by Waka Kotahi NZ Transport Agency for all structural anchorage works undertaken from now on.
Waka Kotahi must ensure that its practices deliver proper value and do not cause medium-term issues that are likely to increase costs. In this case, the use of hollow bars as an anchorage and soil nailing method without proper consideration of their suitability to perform the role may have some unacceptable consequences.
The purpose of the notice is to advise that there has been an issue and to ensure action to obviate further instances. It also allows our suppliers to be more aware of our expectations for the importance of suitable design of structural features.
Hollow bars do not comply with the bridge manual in a number of areas including design working life, durability and quality control. Specific approval, through the departure process, will be required to use hollow bar anchors and soil nails as an anchorage method. The departure request will require sufficient evidence to demonstrate significant benefits for Waka Kotahi at reasonable cost and acceptable risk. This requirement applies to all uses of hollow bar anchors including rockfall protection structures.
While all departures are subject to specific approval by Waka Kotahi, generally such departures are unlikely to be accepted for major reinforced concrete structures but may be accepted for on-slope rockfall protection structures depending on a number of factors including, but not limited to, slope stability conditions; access; design working life of the anchor/soil nail; maintenance regime and durability of the element; and, head assembly.
Our target audience for this advisory note is generally internal staff giving approvals and those external agents designing road structures on behalf of Waka Kotahi. As a result, our communications will mostly be focussed internally.
Advice of these changes will be promulgated by:
The implementation should be fairly simple as the audience is specific and small. The aim is to target that audience using the communication exercise.
Given this update is a single, specific issue, it was not considered necessary to conduct company-wide, specific training on the changes.
It is important to check that this this has been delivered effectively and the desired outcome achieved. A review of the effectiveness of the changes will be undertaken by sampling the designs used for a number of structures, particularly slope protection, used in road construction projects. Should the advice not be being heeded, a larger sample will be taken to establish the problem size and a further communication exercise will be undertaken.
Author: Waka Kotahi New Zealand Transport Agency
Published: April 2020
Version: 1
Found at: https://www.nzta.govt.nz/roads-and-rail/highways-information-portal/technical-advice-note/
If you have any questions or feedback, please contact the Lead Advisor - Geotechnics at geotechnics@nzta.govt.nz
David Darwin - Chair, Ratification Group
Vanessa Browne - Delegated Approver
