Research to reduce geotechnical uncertainty and understand the cumulative impact of seismic events on earth dam performance

Why earth dams?

New Zealand has a large number of earth embankment dams, many of which were designed from the 1920’s through to the 1980’s to enable hydroelectric power generation and provide reliable water storage. Given that hydropower generation accounts for approximately 55% of total electricity generation in New Zealand, earth embankment dams form a vitally important part of New Zealand’s energy infrastructure.  The agricultural and viticultural sectors of New Zealand increasingly rely on embankment dams for irrigation purposes; and many urban centres rely on large earth dams for reticulated water supply.

Accordingly, earth dams are of significant economic importance to New Zealand.  Any potential loss would be felt both functionally (power outages or failure of water supplies) and in terms of damage or death that could result from an embankment dam failure. 

What concerns do we face?

Many of the world’s large earth dams were constructed before the evolution of current engineering design standards. A number of recent international sinkhole and erosion incidents suggest that some mechanisms of dam failure could take many decades to manifest at a visible scale. All over the world, the dam engineering community is calling for an improved science-based understanding of long-term earth dam performance. Compounding these long-term performance uncertainties is New Zealand’s highly seismic environment.

Hydropower asset owners in New Zealand have expressed a need for improved guidance for evaluation of embankments following earthquakes. Engineering ‘knowledge-gaps’ are identified as key concerns:

• Dam engineers presently lack a comprehensive understanding of New Zealand’s dam assets.  
  • New Zealand does not have a national dam inventory.    
  • The geotechnical properties of many large structures remain uncertain.
• The influence of dam and abutment geometry on core deformations is poorly understood.
• There exists considerable uncertainty surrounding the behaviour of filter and transition soils during, and following, seismic loading.
• We possess a limited understanding of the response of earth embankments to successive periods of ground shaking – that is, the cumulative effects of earthquake events occurring throughout the entire life of the dam.

Recent updates

How will the UCQC Earth Structures Research Team address these concerns?

The UCQC Earth Structures project was developed to address local industry concerns and advance the state of dam engineering both in New Zealand and internationally.

The project is presently supported and guided by three leading dam asset owners: Genesis Energy, Meridian Energy, and Mighty River Power. Governance is provided by a steering committee comprising representatives from industry partners, along with Peter Amos of Damwatch Services Ltd.

Additional guidance is provided by local engineering consultants and members of the New Zealand Society of Large Dams (NZSOLD). Existing links with world-class international researchers will be further developed as the project progresses.

The key performance concerns will be addressed within core research modules 1.1 to 2.3, illustrated above. The research methods will include:

• Analytical and empirical desk analyses to screen for geotechnical susceptibilities
• Scale-modelling of embankment deformations using international apparatus (Module 2.1)
• Commissioning of novel laboratory apparatus at the University of Canterbury to assess particle migration in soils under steady-state and seismic loading conditions (Module 2.2)

What are the expected outcomes?

The aim of the research project is to develop an improved understanding of deformation and erosion phenomena.  The project will provide science-based decision-support tools to help asset owners manage risk, prioritise improvement works, and improve post-earthquake inspections.

The commissioning of a specialized seepage testing facility in New Zealand will benefit the dam community directly (testing of dam materials) and indirectly (via research outcomes and the local availability of equipment and expertise).  At a broader level, the UC Quake Centre Earth Structures Research Project aims to create a world-class research community at the academic-industry interface.  The project will grow capability in New Zealand, both within industry and research faculty, and develop sought-after internationally-recognized expertise.

Who will benefit?

Research outcomes will set the stage for improved dam risk management across New Zealand in coming decades.

• Asset owners will benefit from reduced uncertainty in the assessment of earth dam performance, and will gain science-based frameworks to aid in minimising financial and performance risks associated with aging earth dams.
• The academic community will benefit from the concentrated investment of resources and expertise in the field of geotechnical dam engineering. International research collaborations will provide enduring links to facilities with complementary expertise and specialist equipment.
• The New Zealand dam engineering community will benefit from research outcomes and the development of local, world-class, capability in the field.
• The New Zealand public will benefit by way of improved reliability of power and water supply, and safer dams.