Retaining walls are part and parcel of hillside living, but fixing them post earthquakes has brought repair and insurance challenges.
Ministry of Business, Innovation and Employment (MBIE) has released technical engineering guidance on the seismic design of residential retaining walls in the Port Hills. Failure of retaining walls can cause serious damage to houses and neighbouring properties.
The guidance is part of the Repairing and rebuilding houses affected by the Canterbury earthquakes residential guidance document.(external link)
Most of the affected retaining walls, which are the focus of this document, are for residential sites in the Port Hills of Christchurch. However, the same design principles will be applicable to other residential sites in the city, although ground conditions may be quite different.
The guidance has been developed following a robust process of expert consultation. It has been informed by a review of international literature and from observations of how retaining walls performed in the Port Hills during the earthquakes.
The guidance is technical and aimed at professional engineers competent in the design of retaining walls to assist them while they are working for homeowners to design retaining walls that adequately withstand the effects of earthquakes.
Following the earthquakes, the Council, along with Stronger Christchurch Infrastructure Rebuild Team(external link) (SCIRT), has worked on retaining walls which posed a danger to public safety or blocked public access routes.
In cases where the Council is responsible for retaining walls, SCIRT will be responsible for their reconstruction and will inform households in the area well in advance of any construction work.
In cases where homeowners are responsible for a retaining wall, they will need to work with the Earthquake Commission(external link) and to contact their insurer to check whether their insurance policy covers retaining walls.
To assist with this process we have produced a booklet detailing common scenarios: Determining responsibility for retaining walls [PDF, 884 KB] [PDF 800KB].
If you require further information or assistance, please contact us.