Seismic resilience of underground lifelines: Case study of the Christchurch City potable water network
X. Bellagamba
The recent 2016 Kaikoura earthquake and the 2010-2011 Canterbury Earthquake Sequence illustrated the devastating effects of earthquakes in terms of their impact on economic, social and personal life of the entire community. While significant efforts have already been devoted on the improvement of the building inventory, less attention has been devoted to spatially-distributed infrastructure providing crucial services like transportation, water, power, telecommunication or sewerage. The purpose of this thesis is to explore and improve the resilience of underground infrastructure, and to develop a framework of advanced concepts of seismic performance assessment for distributed infrastructure. The case study selected to illustrate the developed concepts and tools is the water distribution network of the city of Christchurch both in the context of the Canterbury earthquakes and also future seismic hazards in the Canterbury region.
This study can be decomposed into five different elements of research. First, fragility functions for buried pipelines in liquefaction-prone soils are developed using the Canterbury earthquake dataset. To make this model widely applicable, unknown parameters are replaced by random variables, increasing the uncertainty of the model. It should improve the accuracy of loss assessment studies for underground pipe network in liquefaction-prone soils.
Second, network resilience analyses are conducted. These analyses cover the seismic performance of the network as well as the recovery of its functionality. Results are given in terms of potential service reduction, as models are currently unable to accurately predict the amplitude of a single pipe failure. Three types of analyses are conducted: historical cases (e.g. 2011 February earthquake), scenario analyses (e.g. Alpine fault rupture, Porter Pass fault rupture) and probabilistic analyses. The results obtained will help communities improving their preparation to such events.
The third objective aims to quantify the probabilistic seismic hazard effect on the long-term maintenance costs. The realization of this objective will help network managers to provision their finances accordingly based on their accepted risk.
The penultimate objective is to estimate the benefits of pipe replacement given the applied maintenance strategy. The quantification of the potential benefits can help network operators and decision-makers to select the appropriate strategy given their available resources and goals.
Finally, the last objective is devoted to the development of a tool to estimate the most probable break locations following an earthquake. It can serve as a post-disaster decision-support tool to prioritize inspections and repairs, where they are most needed, and thus to reduce the global impact on the community.
In summary, the combination and application of the aforementioned research elements delivers new, efficient and intelligent tools to help decision-makers improve the seismic resilience of their social units (community, network operator company, insurance company or other). This should lead to a comprehensive mitigation and transfer of the seismic risks as well as a reduction of the earthquake impacts on their social units.
Impact
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