Ian Froggatt, senior geotechnical engineer, Aurecon. This paper was first published in GE’s February 2015 edition.
On 4 September 2011, 22 February 2012, and 13 June 2012, Christchurch suffered major seismic events. As well as the loss of life and extensive damage to buildings that occurred, more than 2,000 retaining walls of various heights and types of construction were damaged. The damage ranged from minor movements to total collapse.
The author moved to Christchurch in October 2011 to begin work at the Stronger Christchurch Infrastructure Rebuild Team (SCIRT), where the main focus of his work has been the assessment and remediation of retaining walls owned by Christchurch City Council (CCC). The type of wall has ranged from relatively low height stone facing structures which are little more than erosion protection faces, to concrete crib walls, timber pole structures and gabion and reinforced fill structures over 6m high.
This paper presents the author’s observations concerning the general behaviour of, and type of damage suffered by, the walls he has inspected, some possible structural reasons for the mode of movement, the remedial solutions adopted and a summary of some measures SCIRT has adopted for specific walls in an attempt to improve seismic resilience.
The paper does not discuss technical analysis or design in detail, but instead aims to cover what has been learnt from observations of retaining wall damage and provides a general overview of how retaining walls have been remediated in Christchurch.