Quality Over Quantity: Today’s Bridge & Tunnel Inspection 

Shane D. Boone, Ph.D., Chair of ASNT Research Council Infrastructure Committee

It’s no secret that the aging infrastructure across the United States poses a risk to the safety and serviceability of our nation’s structures. While other industries have implemented preventative maintenance methodologies for preservation of their assets, the transportation infrastructure industry has lagged and primarily utilizes a retroactive approach.  An example, Amtrak’s B&P Tunnel Replacement Program, seeks to replace the nearly 150-year-old B&P Tunnel in Baltimore, MD that is currently used to transport thousands of commuters daily along its Northeast Corridor (NEC). The decrepit tunnel is plagued by a range of issues, including excessive water infiltration, structure deterioration, and floor sinkage. Had the tunnel been properly inspected and evaluated on a routine interval throughout the 20th century, emerging flaws and defects may have been addressed in a proactive effort to prolong the tunnel’s lifespan.  While the current National Bridge and Tunnel Inspection Standards (NBIS and NTIS, respectively), recognize a proactive inspection process, there exist technologies that could improve the data gathered such that more informed decisions could be made by asset owners.

Nondestructive Testing and Evaluation (NDT-E), is a form of inspection that can be performed without impacting a structure’s integrity. Cracks, corrosion, discontinuities, or structural degradation, for example, can be identified long before they are reported with visual inspection. Utilizing NDT-E can provide key structural and material data allowing stakeholders of transportation infrastructure to better allocate their funding through more effective and efficient inspections.  These inspection methodologies can also potentially improve the safety and longevity of the structure(s) while maintaining the safety of
inspection personnel. 

The digitalization of the inspection industry has led to the adoption of new technology and tools for NDT-E personnel to assist in meeting federal inspection requirements. There are currently sixteen recognized methods of NDT-E across a range of industries and for the infrastructure of bridges and tunnels. 

Visual Testing (VT) is a technique of NDT-E inspection, and it can be utilized as an important method of risk assessment. VT involves the visual observation of the surface of a test object to evaluate the presence of flaws or defects in the material. VT is the most used test method in the infrastructure inspection industry, as most test methods require personnel to visually inspect the surface of a part prior to inspection. There are two visual testing techniques: direct, which involves the use of optical instruments for the inspector to physically observe the material; and remote, which involves the use of borescopes, drones, cameras, and computer-assisted viewing systems to identify possible issues within a structure.

Visual Testing is a vital first step in the routine inspection of any element of infrastructure, including bridges and tunnels. With the constant adoption of new technology in inspection software, the method and quality of data collection can be consistently improved. High resolution image (HRI) data collection via drone or other traveling vehicle can allow for a thorough record of an asset’s existing surface condition, that can potentially be compared year over year.  While this process can be implemented fairly easily, the current lack of standards related to the image data collection and subsequent resolution of the final deliverable has potentially caused a slower implementation of these types of tools. 

Federal Regulations from the Federal Highway Administration

Close, visual inspection of bridges and their spans is the first step of federally mandated bridge inspection. This is set by the NBIS and NTIS, which incorporate inspection regulations and protocol for bridges and tunnels, as noted above. Visual Testing is implemented with routine, hands-on inspections as well as in-depth inspections when potential flaws and defects are observed.

Inspection personnel must possess certain qualifications, including completion of a Federal Highway Administration (FHWA)-approved comprehensive bridge inspection training course. Inspectors must also take a refresher course every 60 months to ensure their skills are up to date with the latest technology and tools.

The current inspection standards for bridges are calendar based. Each bridge must be inspected at regular intervals not to exceed 24 months. Depending on the integrity of the bridge, some need to be inspected once every 12 months while others can expand their inspection frequency to once every 48 months.

Importance of New Technology in Visual Inspection

As mentioned above, HRI can be utilized to create visual records, including 3D models of a structure, that can be used to visually track how structural elements change over time and if flaws and defects emerge between inspection cycles. These 3D models can be used year after year to compare versus having still images taken from
different vantage points. 

In the last decade, methodologies have been improved to allow data collection at highway speeds, via drone, and fixed wing aircraft to capture visual data that can be stitched together into orthomosaic images. This has resulted in the creation of automated algorithms for crack, spall, and patch detection in concrete structures and surface crack and corrosion detection in steel structures. This enables a more efficient, reliable, and repeatable inspection which ultimately saves on cost and time, while also reducing the impedance on the
traveling public. 

VT is not just about efficiency, but also safety and effectiveness. It adds great benefit to the inspection process by reaching areas that are otherwise inaccessible or dangerous to access while maintaining the safety of inspection personnel. In addition to removing the potential safety risks when inspecting difficult to reach areas, utilizing HRI increases effectiveness through image resolution and
identifying discontinuities. 

While there have been many advances in the collection and processing of HRI, there are currently no standards for the resolution of the data captured and subsequent deliverable. This causes a challenge for inspectors as they then must recollect and restitch the data, incurring more time and cost. This could be avoided by setting a standard for the resolution of images captured from the inspection while still allowing inspectors to select their tools.  This standard should match that required by both the NBIS and NTIS, however, this level of resolution is difficult to achieve and can result in higher costs to the asset owner.   

Being More Effective with Visual Inspection

Visual inspection and supplemental HRI should be utilized to the fullest extent possible by having standard training on new equipment and software as well as standardization of data resolution and deliverables.  Properly utilizing these tools can provide asset owners with reliable, repeatable data that can be utilized to improve data driven decision making.  With limited resources, these asset owners can implement more efficient inspections that will be critical to our aging infrastructure.