In the 1970s, the National Bridge Inspection Standards were established. They established criteria for which bridges should be inspected, how often they should be inspected, and who is qualified to do it. Vehicle bridges that are longer than 20 feet and open to the public must have frequent inspections by qualified visual inspection bridge inspectors, according to the NBIS. Routine above-water inspections are performed every 24 months. Bridges with elements that cannot be accessed without diving equipment must have underwater inspections every 60 months at the most.
Why Perform Underwater Inspections?
As previously stated, essential bridge structural components reside beneath the waterline, and periodic inspections by experienced underwater bridge inspectors help to protect bridges and commuters who use them. However, looking for scouring erosion of soil surrounding bridge foundation elements underwater bridge inspection is an extremely crucial aspect of those assessments. A comparison of the current groundline elevation to past elevations is also carefully studied during routine inspections.
According to the Federal Highway Administration, is the most common cause of bridge failure in the US. The National Bridge Inventory lists thousands of bridges as scour essential. Scour can have disastrous consequences if there are no appropriate safeguards in place.
What is Scour?
Scour is the leading cause of bridge failure in the United States. It is a naturally occurring process in which running water removes riverbed silt from around bridge piers and abutments. Scour can ruin infrastructure and undermine bridge foundations if proper design and safeguards are not in place.
How Are Bridges Inspected Safely in High-Water Events?
During high-water occurrences, such as a flood, the best time to assess bridge scour is in real-time. Unfortunately, owing to the high currents, little clearance beneath the bridge, and shifting debris piles caused by turbulent, swiftly moving water, this can also be the most dangerous and troublesome time for divers to inspect a bridge. The most efficient way to keep inspectors safe at these times is to keep them out of harm’s way, which is made possible by unmanned surface vessels and other sonar technology.
They’re fast, nimble, and self-righting in strong currents, and they’re similar to remote-controlled boats, though some seem more like buoys. They were created for a variety of research purposes, and certain models have also been converted to aid in search and rescue missions. Many types of USVs have been modified to allow for scour inspection from the shore. Scanning with these nimble devices has a number of advantages, including:
- Increased safety by removing the need for a diver or inspector to enter the water during harsh weather. USVs can be controlled from a nearby safe location.
- Inspections must be completed in a timely manner, hence quick deployment is essential.
- Inspection capabilities in the event of a high-water event
- Sensors and cameras are used to acquire accurate, real-time data and send it back to shore.
The USV or other remotely driven vehicles are not a substitute for qualified inspectors inspecting items up close and personal. Qualified diver inspectors go underwater to undertake assessments of the channel features and those portions of the bridge below water during regularly scheduled inspections and in unanticipated situations, such as shortly after flood levels recede. The intensity of underwater inspections is possible.