The Benefit of Spatial Correlation for Non-Redundant Lifelines

Lifelines such as pipelines, telecommunication conduits, power transmission lines, transportation corridors, and other linear systems dominate our civil infrastructure. These linear systems are often non-redundant but are essential for a functioning society. These systems rely on the their foundation soils to provide resistance to static loading from dead and live loads and to dynamic loading from seismic, wind, wave, and other transient hazards. Although typically neglected in lifelines design, the spatial correlation of resistance and the spatial correlation of loading result in a lower probability of failure for non-redundant lifelines. In this paper a simple example of a bridge subjected to liquefaction is used to demonstrate the reduction in probability of failure that spatial correlation affords. A discussion of how this may affect design procedures for lifelines is presented. Additionally, typical spatial correlation distances are examined for soil resistance and for seismic loading. The goal of this paper is to foster discussion about the importance of spatial correlation for civil engineering works. By accounting for spatially variability in load and/or resistance it is shown that the system probability of failure is less than the typical assumption of statistically independent components. The fact that foundation soil resistance is spatially correlated and strong ground shaking is spatially correlated supports the argument that this should be included in the design of spatially distributed lifelines.