NZ Geotechnical Society (NZGS) 22nd Symposium 2025 Auckland
There is continuing pressure to reduce carbon emissions from infrastructure projects as part of New Zealand’s emissions reduction plan. Retaining walls can have significant embodied carbon due to the quantities of materials above and below ground level. This paper explores the whole-of-life embodied carbon of different types of retaining walls.
Previous research has typically compared the embodied carbon of retaining wall options for a hypothetical project or focused on sustainability of a specific wall type. This research paper sources data from over 500 detailed retaining wall designs from real projects around New Zealand. Data is considered for concrete pile, sheet pile, post and panel, gravity, MSE and timber pole walls. The design drawings for each wall show weights and volumes of materials per linear metre, which have been measured and factored by published data for embodied carbon of construction materials. The type of wall and the retained height have been used to make meaningful comparisons between the data.
The data shows a clear correlation between embodied carbon and wall height, where embodied carbon increases with the height of the wall. The embodied carbon is also dependent on the type of retaining wall, where a concrete pile wall has significantly higher embodied carbon than a timber pole wall for a similar retained height. This research demonstrates that significant impact on embodied carbon can be achieved early in the concept design stage by working with clients and constructors to reduce the required retained height or to adapt design constraints to enable a retaining wall type with less embodied carbon.
