High-resolution sonars set to revolutionise bridge scour inspections

Abstract

As rainfall intensities increase so does the risk of scour damage to river crossings. Scour inspections are traditionally carried out by divers, but the water around bridge piers is often turbulent and murky such that little can be seen. This paper reports on a trial inspection of the underwater foundations of the 1889River Hamble railway viaduct in Hampshire, UK using state-of-the-art high-resolution sonar and marine laser technologies. The trial was so successful it could transform the way such inspections are carried out in future. Three different sonar systems and a laser scanner produced a holistic assessment of the viaduct structure above and below the waterline. A three-dimensional record of all scour erosion features was digitally mapped along with the condition of the substructure. Significant scour was identified, contradictory to previous diver-based assessments. As discussed in the paper, sonar technologies can be rapidly deployed for emergency inspections as well as be immersed longer term for routine or periodic assessments. BackgroundThe UK climate impacts programme (UKCIP) supplies a range of future scenarios driven by likely climate change in the UK up to 2080, predicting that extreme rainfall events will become more frequent and intense. This climate scenario poses increased risk for UK railway bridges since extreme rainfall is associated with violent flood events that ultimately threaten bridge foundations as they substantially worsen scour.It is widely accepted that scour is one among the most common causes of bridge failures and therefore it is imperative to establish strategies to assess resilience against future and more violent hydraulic load cases.There are approximately 60 000 highway and railway bridges that cross watercourses in the UK. Many of these structures are in excess 150 years old with foundation depths that are either uncertain or simply unknown. Archive records for these structures can sometimes be out-of-date or missing altogether. A significant number of bridges are extremely susceptible to scour as a function of hydraulic and geotechnical conditions.No well-established inspection methodologies currently exist that can adequately reveal the physical processes, conditions and likely extent of scour to bridge foundations (Manes, 2014). As a direct consequence, engineers charged with the responsibility of design or assessment cannot readily underwrite structural performance and longevity leaving a residual concern connected to risk management and limiting the possibility of catastrophic failure.The most common methodology to assess scour and the net risk of future scour in rail bridges is based on surveys carried out by commercial divers. It is readily appreciated that inspection by diving suffers from considerable limitations related to poor visibility in water. In fact, it is quite plausible for divers to overlook critical defects if the area for concern does not fall within the inspection track followed by the diver and support craft.Bridge scour is primarily caused by the...

Assessing the suitability of bridge-scour-monitoring devices

“…The review of Imam & Chryssanthopoulos (2012) reported that 17% of metal bridge failures (in the UK) were due to scour. The UK has over 87,000 bridges (RAC foundation, 2020) which comprise an ageing stock and which often have unknown (or uncertain) foundation depths (e.g., Clubley et al 2015). Diagnosis of scour problems for bridge structures is also more challenging than for other 'damage detection' tasks, as the damage is often obscured from view by the water surrounding the piers.…”

“…This presents a major forensic engineering challenge for both visual inspection and more complex Structural Health Monitoring (SHM) systems. In particular, if the water level is above the level of the bridge foundations, then the exposure cannot be assessed from the riverbank (e.g., Ko et al 2010;Selvakumaran et al 2018); and when this happens, a diving team must be deployed in waterways where underwater visibility is often poor (e.g., Clubley et al 2015).…”

“…Scour effects may be more frequent and unpredictable if weather patterns change and floods increase in their frequency and scale due to climate change (cf. Clubley et al 2015;Dikanski et al 2017). For bridge engineers undertaking investigations and assessments of bridge assets, SHM systems may be helpful if the outputs they deliver in terms of data (and subsequently information) are directly linked to key decisions that the asset owner needs to take (e.g., maintenance, closure, or replacement of a bridge structure) (e.g., Vardanega et al 2016).…”

Electromagnetic Sensors for Underwater Scour Monitoring

“…(1) Pulse or radar devices [16][17][18] High Medium (2) Single-use or float-out devices [19] Low Medium (3) Fiber-Bragg grating systems [20,21] Low Low (4) Sounding or driven rod systems [19,22,23] Medium Medium (5) Sound wave devices [24][25][26] High High (6) Electrical conductivity devices [27] High Medium (7) Dielectric probes [28] High Medium Indirect Scour Measurement Devices (8) Tilt sensors [19,24] Low (9) Accelerometers [26,[29][30][31] Low (10) GPS [32,33] Medium (11) Satellite [34,35] Low…”

Editorial

“…The paper by Clubley et al (2015) introduces an exciting new trial of how sophisticated high-resolution sonar in conjunction with marine laser techniques has been applied to review the existing river foundations of a rail bridge in the UK. Its application allowed the inspection engineers to determine rapidly and comprehensively a three-dimensional record of the scour erosion.…”