Chirstchurch: 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 storm-water 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 wether 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.