Christchurch: Pipelines

Earthquake Concerns on Underground Pipes

• Wave propagation

• Permanent ground deformation

• Liquefaction

• Can lead to pipe leakage and/or pipe breakage

• Broken sewer pipes near Christchurch are pumping raw sewage into the water leading to the closure of many popular beaches.

• Several cases on gastrointestinal illness reported

• Susceptibility to pipe damage is mainly dependent on the material of the pipe and the earthquakes intensity.

• To a smaller extent factors include nature of surrounding sediments, pipe length and diameter, and amount and type of pipe joints.

Pipe Materials in Response to Earthquakes

• Steel and iron pipes carrying natural gas are prone to leakage or breakage especially at pipe joints and seams.

• Brittle concrete and PVC pipes that carry water or sewage are prone to fracture.

• Flexible high density polyethylene pipes respond best to ground acceleration due to earthquakes.

• Clay pipes make up over 300 km of the sewage and stormwater pipes under Christchurch. Almost all of the pipes inspected thus far were blocked or broken.

Damage• There was heavy damage to water and sewer pipes. Fifty percent of

wastewater system remains working, however significant damage was done to the water treatment plant.

• Sewer pipe leaks and silt blockages are causing raw sewage to flow into the Heathcote and Avon rivers and is expected to continue for months to come.

• The extent of damage to pipelines in Christchurch is still unknown but will continue to mount as infrastructure rebuilders get into the roads to carry out work.

• Even though there were gas leaks there were no major gas fires after the earthquake.

Ocean Outfall Project

• Opened March 24 2010

• Cost: $87.2 million

• 5 km of new pipeline, extending 3 km offshore

• Connects to 150,000 households in Christchurch

What is Ocean Outfall?• Includes new pump at Christchurch Wastewater Treatment Plant

oxidation ponds

• 2.3 km of concrete pipe onshore- dredge and lay

• 2.7 km polyethylene marine pipe into Pegasus Bay- mircotunneling

• Project to replace Avon-Heathcote Estuary due to concerns about marine environments and human heath.

• Discharges treated and disinfected wastewater out at sea

• After inspection the Ocean Outfall project seems to be intact.

• Prior to the earthquake three more ocean outfall projects were expected to take place to deal with wastewater treatment and disposal in Lytellton, Diamond Harbor and Governors Bay.

• Considerations must be made regarding whether or not ocean outfalls are the best strategy for wastewater management in earthquake prone zones.

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• With increasing migration of peoples to the Christchurch area, large scale land based wastewater treatment plants may not be desirable.

• Ocean outfalls may continue to be the solution for the increasing human waste disposal for this region.

• Therefore planning, construction, and maintenance of new systems should be well discussed and thought out.

Future suggestions • Using pipes of ductile nature.

• Larger diameter pipes fair better.

• Compacting ground before pipe laying.

• Injection of cement to bind sands and gravels.

• Designing simple networks with minimal joints.

• Installing perimeter walls in ground.