Remote monitoring to predict bridge scour failure using Interferometric Synthetic Aperture Radar (InSAR) stacking techniques

Sivasakthy Selvakumaran,Simon Plank,Christian Geiß,Cristian Rossi,Campbell Middleton

doi:10.1016/j.jag.2018.07.004

Abstract

Scour is the removal of ground material in water bodies due to environmental changes in water flow. It particularly occurs at bridge piers and the holes formed can make bridges susceptible to collapse. The most common cause of bridge collapse is due to scour occurring during flooding, some failures causing loss of life and most resulting in significant transport disruption and economic loss. Consequently, failure of bridges due to scour is of great concern to bridge asset owners, and is currently very difficult to predict since conventional assessment methods foresee very resource-demanding monitoring efforts in situ. This paper presents evidence of how InSAR techniques can be used to monitor bridges at risk of scour, using Tadcaster Bridge, England, as a case study. Tadcaster Bridge suffered a partial collapse due to river scour on the evening of December 29th, 2015 following a period of severe rainfall and flooding. 48 TerraSAR-X scenes over the bridge from the two-year period prior to the collapse are analysed using the small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) approach. The study highlights a distinct movement in the region of the bridge where the collapse occurred prior to the actual event. This precursor to failure observed in the data over a month before actual collapse suggests the possible use of InSAR as a means of an early warning system in structural health monitoring of bridges at risk of scour.

Highlights

Scour has caused the failure of hundreds of bridges globally in recent decades and is the primary cause of bridge failure in the United States (National Academies of Sciences, Engineering, and M., 2009)
The results demonstrate the potential of interferometric synthetic aperture radar (InSAR) X-band data to be incorporated into a methodology to detect unusual deformations in masonry arch bridge structures, with a potential capability to be integrated into structural health monitoring systems as a means of giving early warning of scour failure
InSAR stacking techniques were applied to a stack of 48 X-band synthetic aperture radar (SAR) images taken over Tadcaster Bridge in a two-year period preceding its partial collapse in December 2015 due to scour failure

Summary

Introduction

Scour has caused the failure of hundreds of bridges globally in recent decades and is the primary cause of bridge failure in the United States (National Academies of Sciences, Engineering, and M., 2009). In the United Kingdom, the increase in rainfall and flooding events in recent years has exacerbated this problem and contributed to the collapse of multiple bridge structures. It can be defined as the excavation and removal of material from the bed and banks of streams as a result of the erosive action of flowing water (Hamill, 1999). This erosive action in the vicinity of bridge piers can lead to the removal of ground material on which bridges are founded, increasing the risk of undermining bridge piers and resulting in collapse. The collapse of bridges and other structures in or adjacent to water bodies highlights the essential importance in finding new methods to undertake inspection and structural health monitoring (SHM) of bridges to identify precursors indicating signs of impending failure

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Discussion

Conclusion