Introduction: The Role of Non-Destructive Testing and On-Site Challenges

In Japan, bridges and tunnels built during the period of rapid economic growth have been in service for more than 50 years, and ensuring the safety of these aging structures has become a major social issue. In fact, there are said to be around 700,000 road bridges and more than 10,000 road tunnels nationwide, making countermeasures against aging urgently needed. Regular non-destructive testing (NDT: Non-Destructive Testing) is indispensable to keep such infrastructure healthy. Non-destructive testing is a collective term for inspection methods that examine deterioration and damage without destroying the object; it is used to detect cracks, corrosion, deformation, and the like in structures so that countermeasures can be taken early. Typical methods include close visual inspection, sounding inspection, and ultrasonic testing, but these are tasks that place a heavy burden on field technicians.

On site, there are many inspection targets, many of which are located at height or in confined spaces, so carrying out regular inspections alone requires considerable effort and time. For example, close visual inspections of road bridges and tunnels are generally mandated by law every five years, generating enormous inspection demand across the country. However, combined with a shortage of technicians and an aging workforce, efficiently inspecting many structures with limited personnel is a major challenge.

Inspections also rely heavily on individual technicians’ experience and intuition (subjectivity), and recording methods are still mainly analog, such as handwritten field notebooks or photo-attached reports. As a result, not only is the workload heavy, but the accuracy and reproducibility of the data tend to vary. In many cases, inspection results that were painstakingly obtained are not fully utilized and end up merely filed away.

Limitations of Conventional NDT Methods

Conventional infrastructure inspections required photographs taken with a camera and measurement values from instruments to be recorded separately. For example, when investigating cracks on a concrete surface, upon detecting an anomaly visually one would photograph it with a digital camera, then measure the width with a ruler or crack scale and write the dimensions in a notebook. Because imaging devices and measuring devices are separated, it is not intuitively clear later which measurement corresponds to which photo, making reconciliation during report preparation time-consuming. Marking damage locations on paper drawings or transcribing into spreadsheet software makes the recording work cumbersome and prone to errors.

Such manual, paper-oriented inspections also leave issues with data reproducibility and cumulative use. If deterioration locations identified during an initial inspection are overlooked or cannot be located during a subsequent inspection, it becomes difficult to track changes over time. When each inspector records data in different formats or focuses on different aspects, valuable inspection data may not be effectively used and simply end up compiled into reports and filed away. Furthermore, there has been no simple way to share or analyze measured values on site, causing time lags in identifying problem areas and sharing information among stakeholders. As a result, time is often consumed organizing hundreds of photos and producing reporting drawings, and administrative work can take more time than on-site work.

“See, Preserve, Measure” NDT Achieved by Smartphone + LRTK

To address these issues, in recent years digital transformation (DX) of inspections using ICT and robots has been promoted. Among these, approaches that utilize everyday smartphones are expected to penetrate field practices. Some modern smartphones, such as the latest iPhones, are equipped with LiDAR (Light Detection and Ranging) sensors, high-performance cameras, and GPS, enabling sophisticated spatial measurement in a compact device. Even smartphones without LiDAR can acquire point clouds via photogrammetry by reconstructing 3D models from multiple photos, but photogrammetry requires many photos and processing time, so using a LiDAR-equipped device is more efficient. By combining this with an outdoor GNSS receiver device, "LRTK," which enables centimeter-level positioning (half-inch accuracy), a single smartphone quickly becomes a high-precision 3D scanner and surveying instrument. LRTK is a pocket-sized RTK-GNSS module that attaches to a smartphone and uses correction data from satellites (such as the Quasi-Zenith Satellite System) to enhance positioning accuracy in real time (positioning accuracy is about horizontal ±2 cm (±0.8 in) and vertical ±3 cm (±1.2 in)). As a result, each point in the point cloud acquired by the smartphone is tagged with latitude, longitude, and elevation information, making global-coordinate 3D records—which were difficult to achieve before—easily possible on site.

With a smartphone + LRTK, the previously separate tasks of “seeing, measuring, and recording” can be accomplished at once. Scanning a structure’s surface with LiDAR visualizes the site as a three-dimensional model, allowing cracks and deformations to be checked in three dimensions on the spot. Because high-density point clouds and photos are tied to positional coordinates, important deterioration locations can be reliably preserved as digital records. Of course, dimensions can be freely measured later on the point cloud model, eliminating the need to “re-measure crack widths with a ruler while looking at drawings later.” It is fair to say that “see, preserve, measure” inspections can now be achieved with just a smartphone.

Furthermore, data measured on the smartphone can be uploaded to the cloud for centralized management. Previously, sites could only share photo data and paper reports individually, but sharing point cloud data in the cloud allows the office to instantly grasp the 3D situation on site. Stakeholders can collaborate in real time by discussing deterioration while viewing the same model. Each photo also carries map coordinates and orientation information, making it intuitive to know “which structure and which location this photo shows,” markedly improving the accuracy of reports. Coupled with intuitive smartphone app operation, the technology is easy to use for both veterans and newcomers, helping to eliminate knowledge silos. By digitizing inspection results in this way, reproducibility and objectivity improve dramatically, enabling consistent-quality recordings of conditions regardless of who conducts the inspection.

Benefits by Use Case: Bridges, Building Exteriors, Piping, Buried Utilities, Pavement

3D records created with a smartphone + LRTK demonstrate power across virtually all infrastructure inspection scenarios. Here are the concrete benefits by application.

• Bridges: Inspections of bridges and elevated structures face the challenge of accessing high or hard-to-reach areas such as under girders. A smartphone 3D scan can accurately record the shape and damage of structures within reachable range without scaffolding or an aerial work platform. For example, cracks on the underside of a girder can be preserved as point cloud data with precise position and dimensions, allowing safe analysis and report preparation back in the office. Even when close visual inspections using bridge inspection vehicles are required, performing 3D recording simultaneously ensures comprehensive preservation of inspection results. Accumulating 3D data from each periodic inspection enables quantitative assessment of changes since the previous inspection, aiding prioritization of repairs. Reducing the number of deployments of inspection vehicles and long-duration traffic control through 3D recording can also lower costs and lessen the burden on users.

• Building Exteriors: For building exterior inspections, it is crucial not to miss tile delamination or cracks. Recently, exterior investigations have been mandated for buildings above certain heights, and building owners are required to conduct regular safety inspections. Traditionally, binocular visual checks or sounding with a tapping rod were the norm, but combining smartphone scans allows the entire facade to be recorded as a digital field notebook. LiDAR scanning while close to the exterior from an aerial work platform enables later marking of delamination and cracks on a 3D model in the office, clearly indicating “what deterioration is at which floor and which position” in reports. Fine defects that are hard to convey in planar photos can be shown three-dimensionally, greatly easing explanations to building owners and consideration of repair extents. With repeated incidents of falling exterior materials becoming a social problem, objective records from 3D scans enhance inspection reliability and contribute to responsible maintenance management.

• Piping and Equipment: 3D scanning is also effective for inspecting piping and equipment in factories and plants. Point-clouding complex piping and equipment assemblies ensures corrosion and leakage points are not overlooked. Because measurements can be taken from a distance—even for high-temperature pipes or confined plant interiors—safety and work efficiency improve. Sharing acquired data in the cloud allows remote engineers to advise while viewing the on-site 3D model, facilitating remote support from specialized inspection technicians. Clearances and pipe diameters can be measured on the point cloud and directly fed into repair or replacement planning. Once scanned, repeated site measurements are unnecessary, shortening lead times from inspection to repair design. Measuring deterioration from a safe distance without stopping operations minimizes production impact.

• Buried Utilities: Buried utilities such as water and sewer pipes and cables become difficult to locate after backfilling, but 3D records made with a smartphone during construction enable visualization of invisible infrastructure. Scanning the trench and surrounding area at the time of pipe installation produces a 3D map faithfully reflecting burial depth and pipe routes. Storing this in the cloud and sharing it aids future maintenance excavations and can be used to evaluate interference risks with other works. The Ministry of Land, Infrastructure, Transport and Tourism is promoting three-dimensional records of buried utilities, and such smartphone measurement data will contribute to building unified underground spatial maps in the future. For small-scale projects, companies can complete records in-house without hiring outside surveyors, reducing costs and streamlining construction processes. This also helps prevent damage accidents during excavation caused by incomplete records.

• Pavement: Pavement inspections involve many tedious tasks such as counting cracks and measuring rut depth. A smartphone 3D scan of pavement surfaces captures the entire damage geometry in data, allowing required indicators to be freely computed after returning to the office. For instance, surface steps and unevenness can be analyzed in cross-section on the point cloud to calculate settlement amounts or automatically compute the volume of potholes. If inspectors carry a smartphone during road patrols, pavement conditions can be saved in 3D on the spot and defect data centrally managed on a GIS map. This makes it easy to determine repair necessity on site and accurately estimate repair material quantities, accelerating the PDCA cycle of maintenance management. Accumulated pavement inspection data can also be analyzed to inform repair planning.

Moreover, the acquired 3D data can be easily integrated with existing drawings and other survey data. Overlaying point clouds on CAD drawings or BIM models facilitates smooth consideration of repair plans—for example, visualizing discrepancies with color coding. Advanced analyses, such as comparing past and new point clouds to quantify deterioration progression, are also possible. Data stored in the cloud can be linked with GIS maps and asset management systems, enabling consistent information sharing across site and office, owners and contractors. As data becomes interconnected, inspection efficiency and accuracy will reach new heights. Integration with AI for automated crack detection and displacement analysis is also expected in the future. Smartphone inspection data will play an increasingly important role in the advancement of infrastructure maintenance.

In actuality, following the 2024 Noto Peninsula earthquake, technicians who rushed to the affected sites scanned collapsed and deformed locations with smartphones equipped with LRTK, immediately sharing the high-precision point cloud models and geotagged photos via the cloud. They measured the settlement of utility poles tilted by liquefaction and the depth of road cracks on site, enabling related agencies to rapidly grasp the situation. This is a prime example of how digital inspection methods contributed to speedy decision-making in disaster response, which previously required much time to compile investigation results. High-precision measurements with a smartphone surveying device per person are proving highly effective even in emergency inspections and disaster investigations of infrastructure.

Conclusion: The Future of Infrastructure Inspection Expanded by Simple Surveying with LRTK

The non-destructive testing solution using a smartphone + LRTK addresses on-site inspection challenges while opening new possibilities for infrastructure maintenance. Because it is less expensive and easier to operate than dedicated equipment, it is expected to significantly lower the barrier to on-site DX. With high-precision surveying, measurement, and data sharing possible from a single smartphone, the range of tasks related to inspections has expanded.

The main benefits of introducing smartphone + LRTK can be summarized as follows:

• Efficiency: Greatly reduces the time and effort required for inspections. Paper recording and manual dimension measuring are reduced, allowing a small team to inspect many facilities efficiently.

• Higher accuracy: RTK positioning records location information with centimeter-level precision, improving the reliability of inspection data. Based on accurate dimensional data, deterioration can be quantitatively evaluated. Human reading errors and recording mistakes are avoided, simplifying quality control.

• Improved safety: Because measurements can be taken from a distance, risks associated with working at height or in hazardous areas are reduced. Compared to traditional methods that rely on scaffolding or aerial work platforms, worker safety is enhanced. Reducing the need for scaffolding or lane closures contributes to worker safety as well as less impact on users and cost reduction.

• Information sharing: Inspection data can be instantly shared via the cloud, smoothing collaboration between site and office and between owners and contractors. Experienced technicians can remotely review data and support newcomers. Historical data is accumulated for long-term asset management.

• Versatility: Acquired 3D data can be used not only for inspections but also for repair planning and as-built management. A single smartphone + LRTK can handle surveying and design support, expanding business scope while reducing additional equipment investment. Applications for disaster surveys and as-built drawings are also expected.

Furthermore, 3D data obtained during inspections can be used for simple pre-repair as-built surveying (dimensioning and quantity calculation). Tasks that previously required a separate surveying team can be completed quickly with a smartphone, smoothing the transition from investigation to construction. Using LRTK, coordinates on design drawings can be laid out on site, enabling solo execution of stake driving and layout marking. AR functions can overlay a 3D model of the completed image onto the real landscape to give instructions such as “place a bolt at this position” or “repair this area,” allowing repair planning for defects found during inspection to be handled seamlessly.

In this way, the combination of smartphones and LRTK strongly promotes DX in infrastructure inspection. Equipping each field worker with a high-precision “digital eye” can be expected to prevent missed deterioration, enhance record quality, and speed up decision-making. Why not leverage this new technology that realizes non-destructive testing with a smartphone and usher in a new era of safety, efficiency, and accuracy at your site?