Underground Utilities – Seismic Assessment and Design Guidelines

Much of New Zealand is susceptible to earthquakes as the country is situated at the active boundary between the Australian and Pacific tectonic plates. Our communities and economy depend on being able to respond and bounce back quickly from seismic events.

The vulnerability of underground utilities to damage from earthquakes was highlighted by the Canterbury Earthquake Sequence (CES) of 2010 and 2011. The earthquakes caused significant damage to parts of the underground utility networks in Christchurch and Kaiapoi, disrupting supply to households and businesses and cost several billion dollars to repair.

The CES however is not a one off sequence of events. Much of New Zealand is at a risk of similar sized earthquakes occurring as shown in Figure 0-1. Hence, it is essential to develop underground infrastructure networks capable of withstanding seismic events in a uniquely New Zealand context.

Scope

The Guidelines mainly focus on underground utility networks of:

• Potable water
• Wastewater
• Stormwater

However, they are also applicable to underground telecommunication, power and gas networks.

The Guidelines provide processes that enable practitioners to:

• Identify sections of networks that are vulnerable to damage, to assess the amount of damage likely to occur and estimate the Levels of Service expected after an earthquake;
• Identify measures to improve the resilience of the existing networks. This includes the development of response plans and capital works programmes to improve the robustness and redundancy of the system and to make it easier to restore service after a seismic event. Direction is given on how to incorporate these activities into asset management planning;
• Determine how to restore a network following an earthquake and to assess the long-term implications of the damage sustained;
• Design and install new utilities that provide an acceptable level of resilience.

The Guidelines aim to improve the ability of underground utility networks to function and operate during and following earthquakes for safety, economic and community wellbeing reasons. The Guidelines recognise that earthquakes may cause some limited and manageable damage. Although they do not attempt to prevent all damage, they do seek to help manage and contain it.

The Guidelines are based on findings from a research project titled The Seismic Response of Underground Services funded by the Ministry of Business, Innovation and Employment (MBIE). While the Guidelines draw heavily on information from the CES of 2010 and 2011, they also incorporate findings from other events in New Zealand and include material from other international and national sources.

There is a technical dispute over findings related to concrete pipes which is currently the subject of dialogue between Hynds Pipe Systems Limited and Opus. As a result of those discussions, it is possible there may be some changes to the documents.