Strengthening strategies – overview

This topic looks at strategies to strengthen and remediate ground and structures to improve seismic resilience. More detail can be found in the Ministry of Business, Innovation and Employment’s guidance Repairing and rebuilding houses affected by the Canterbury earthquakes. Section 15.3 of this guidance, which was updated in April 2015, is particularly relevant to these topics.

The New Zealand Geotechnical Society also provides the following detailed guidance for assessing and remediating liquefaction-prone residential sites in the Canterbury region:

While this guidance is intended to assist with ground improvement following the 2010 and 2011 Canterbury earthquakes, it provides useful advice for ground strengthening in other liquefaction-prone areas of New Zealand.

In 2017, MBIE and the Ministry for the Environment published Planning and engineering guidance for potentially liquefaction-prone land, which provides a risk-management approach to the use and development of land in potentially liquefaction-prone areas.

Ground remediation

Replacement techniques – including gravel mats

Densification techniques – including dynamic compaction, rapid-impact compaction, vibro-compaction, stone columns, compaction piles, compaction grouting and resin injection

Solidification techniques – including soil mixing, jet grouting and permeation grouting

Reinforcement techniques – including lattice wall and grid piling methods

Drainage techniques – including permanent dewatering and vertical drains

Strengthening residential buildings

NZS 3604-type pile foundations

Bracing foundations – including bracing perimeter foundations, bracing open pile foundations (sheet bracing and diagonal bracing) and bracing jack-stud frames

Strengthening commercial and public buildings 

Unreinforced masonry

Retaining walls 

Performance requirements – including minimum recommended SLS and ULS performance of retaining structures in various locations

Retaining wall design

Materials selection