Design for Earthquake Induced Movement on Lifelines – The Ferrymead Bridge Experience

Earthquake induced damage to pipelines attached to bridges was a serious problem that resulted from the Christchurch earthquake sequence of 2010 and 2011. Many major pipelines ruptured as a result of vertical movements of up to 500 mm and horizontal movement of up to 1.0 metre towards the rivers.

The provision of flexibility to accommodate major differential movement was a particular concern for the three lifelines crossing the Ferrymead Bridge, two DN 355 PE 100 water-mains and one DN 450 PE 100 sewage rising main. The design brief called for sufficient flexibility to allow for relative movements of up to 0.45 metres vertical (due to liquefaction and settlement) and up to 1.5 metres of movement directly towards the river (due to lateral spreading), all without loss of service. The final design easily allowed for this movement as well as at least 0.5 metres of movement parallel to the river.

The new Ferrymead Bridge was constructed between 2013 and 2015 and its engineering design was awarded a New Zealand Concrete Society infrastructure award – Commendation in 2015 and an ACENZ Innovate NZ silver medal in 2016. Since the earthquake resistant pipeline design was not presented for consideration in this award, this paper has been prepared to document the innovative solution that provided for the design brief parameters.

The design solution, which made full use of the inherent flexibility of polyethylene pipe to accommodate the relative movements with minimal risk of pipe rupture, is described. The critical importance of all aspects of the pipelines was recognised and the rigor applied to QA of all aspects of the pipelines’ construction from pipe quality through welding, installation and pressure acceptance testing is included.