Streamlining Maintenance of Utility Ducts with AR: Visualizing Buried Infrastructure and Reducing Inspection Effort

In recent years, efforts to remove utility poles and place power lines and communication cables underground—so-called “pole-free” initiatives—have advanced to improve urban aesthetics and strengthen disaster resilience. At the heart of this infrastructure is the “common utility duct” installed beneath roads. Although these ducts are unseen civil structures that support urban life, their maintenance requires continuous inspection and careful management. This article explains the structure and importance of underground common utility ducts, outlines the challenges facing current inspection practices, and explores a new solution that uses AR (augmented reality) technology combined with RTK positioning to visualize subsurface infrastructure from the surface and reduce inspection effort. It also introduces how 3D point-cloud scanning, cloud services, and integration with digital ledgers can elevate maintenance practices, and discusses the significance of a simple inspection tool anyone can use by pairing a smartphone with an RTK device. Finally, using our offering “LRTK” as an example, we present an integrated, innovative approach to recording buried assets, applying AR, and surveying, and propose how to deploy it.

What is a common utility duct: the structure and role of a vital underground infrastructure

A common utility duct is an underground structure—typically a concrete conduit under the road—designed to house multiple lifelines such as power cables and communication cables together. By consolidating infrastructures that were previously buried separately into a single location, it becomes possible to supply electricity and communications safely and efficiently without the need for poles or overhead lines. Pole-free initiatives are being promoted in urban areas from the perspectives of both improving scenery and enhancing disaster resilience, and the development of common utility ducts supports these efforts. Removing overhead wires from the streets not only creates a cleaner streetscape and wider pedestrian areas but also helps reduce the risk of outages caused by high winds or fallen trees, thereby improving urban safety. A common utility duct is not merely a box for cables; it is an important infrastructure that underpins urban functionality and safety.

The structure of a common utility duct can be broadly divided into two elements. One is the conduit section where cables are routed, and the other is the handhole section (manhole) provided at regular intervals. The conduit section is a tunnel-like space extending underground where multiple power and communication lines are accommodated. The handhole sections are openings to the surface placed along the conduit at set intervals, providing space for workers to descend for inspection and repair. This configuration allows access to underground equipment without excavating the ground and enables efficient maintenance of multiple operators’ equipment in a consolidated manner.

In practice, introducing common utility ducts substantially reduces the effort required for maintenance inspections and repair works, and offers many benefits such as enabling rapid cable inspection and restoration from dedicated spaces during disasters.

That said, installing a common utility duct is not the end of the work—regular inspections are required to ensure safe long-term operation. Under the Common Utility Duct Act and road manager guidelines, it is mandatory to verify structural soundness on a periodic basis every few years and perform repairs as necessary. Keeping the unseen, buried infrastructure in good condition is essential for citizens’ safety and security. Therefore, maintaining common utility ducts is an important operational challenge for urban infrastructure.

Inspection work for common utility ducts: current methods and the challenges they face

Currently, inspections of common utility ducts are primarily performed by people, using their eyes and hands. The common practice is to open the lids of handholes (inspection openings) installed along roadsides or sidewalks and have workers enter the interior to perform visual inspections. Large ducts may have walkable passages, while smaller conduits are sometimes inspected by inserting cameras or fiberscopes. Inspection items include checking the concrete structure for cracks or leaks, ensuring cables are not damaged or showing abnormal heat, and verifying that drainage systems function properly. Inspectors also pay close attention to interference points with other buried utilities such as gas and water/sewer pipes. Inspection results are recorded through photographs and logbooks, and repair plans are formulated as needed.

However, traditional inspection methods have several noted challenges. First is the issue of workload and time. Because workers must descend into underground spaces for verification, inspections require teams of multiple people; when considering safety watchers and the like, manpower needs increase. Since work takes place on roads, preparations for traffic control and the heavy work of opening and closing manhole covers can extend the time required per inspection location. Common utility ducts often run long distances through urban areas, so performing regular inspections of the entire length demands considerable labor. With current concerns about staff shortages, this workload is a growing burden.

The second challenge is limited visibility. Visual inspections relying on flashlights or portable lighting are inherently prone to oversight. Discovering abnormalities in deep sections of the conduit or in high or blind spots often depends heavily on experience and intuition, so sites lacking seasoned staff can see variability in inspection quality. It is also difficult to grasp the condition of extensive duct networks at a glance, so inspections often must be based on partial information.

Inefficient information management is another issue. Data gathered during inspections (photos and measurements) are often compiled into paper ledgers or reports, making it difficult to instantly compare against past records or to aggregate data from multiple locations for analysis. Sharing information between departments can be time-consuming, and when field conditions differ from drawings, it can be difficult to correct and reflect those differences on the spot. In older ducts, as-built drawings may remain only on paper, creating discrepancies with current conditions. Such analog management can hinder rapid decision-making and planned maintenance.

Finally, safety concerns cannot be overlooked. Entering underground spaces carries the risk of oxygen deficiency or toxic gases, requiring careful preparation and vigilance. The act of opening lids and having workers enter and exit on roadways itself is hazardous and requires caution to protect motorists and pedestrians. As inspection frequency increases, so do the opportunities for exposure to these risks.

As described above, current inspection work for common utility ducts involves significant manpower and time, is highly dependent on individual expertise, and raises safety concerns. One promising approach to addressing and mitigating these issues is the use of AR technology and high-precision positioning (RTK). The next section looks in detail at efforts to use AR to make buried infrastructure “visible” from the surface and to guide inspection tasks.

Visualizing buried infrastructure with AR and RTK: surface-level “see-throughs” to guide inspections

If cables and conduits buried deep underground could be visualized on site without special X-ray equipment, inspection work would become dramatically more efficient.

This capability is enabled by combining AR (augmented reality) with RTK-GNSS positioning. AR technology allows digital information to be overlaid on real-world views through a smartphone or tablet screen. In the case of common utility ducts, pre-acquired subsurface location data and 3D models can be displayed via AR so that, while standing on the surface, users can intuitively visualize which infrastructure runs where beneath the road in front of them.

However, to align AR overlays accurately with real-world positions, a device’s position and orientation must be known with high precision. That’s where RTK (Real Time Kinematic) high-precision GNSS positioning comes in. Ordinary GPS can have errors of several meters, but RTK uses correction information from a base station to improve position accuracy to the centimeter level. By attaching a compact RTK-capable GNSS receiver to a smartphone or tablet, users can measure their position to centimeter accuracy and precisely align AR content with the physical environment.

This AR+RTK “surface-level visualization of buried infrastructure” offers various benefits for navigating inspection tasks.

• Rapid location identification: If the location of a handhole or underground asset to be inspected is not known, AR can display a marker on the ground to show the spot at a glance. There is no need to consult drawings and set up surveying equipment—the worker simply points a smartphone to see “this is the cover to open next.” Digital markers can also prevent oversights during nighttime or low-visibility conditions.

• Shared understanding of subsurface structure: AR can visually reproduce the “mental map” of underground piping held by experienced workers. Less experienced staff can quickly grasp pipe layouts and spatial relationships with other buried assets by viewing AR imagery. By “seeing the unseen,” the entire field team can align their understanding and make accurate decisions.

• Guided inspection items: When linked with a digital ledger that stores inspection items and repair histories, AR can pop up information like “this section was repaired last time” or “this spot has an abnormal sensor.” In effect, AR can present a checklist overlay to support thorough inspections. Even without seasoned personnel on site, AR instructions help standardize inspections.

• Non-destructive confirmation of buried assets: If the location information of buried assets is accurate, AR can reproduce that information visually to confirm positions without test excavations. Combined with 3D scanning technologies described later, AR can, for example, accurately recreate “at what depth and how a previously repaired cable was buried,” allowing teams to evaluate potential interference with planned works. Reducing unnecessary excavation cuts both time and cost.

• Recording and remote sharing: AR views can be captured as screenshots or recordings for documentation. Annotated footage of problematic spots can be shared via the cloud with experts in the office, enabling simultaneous review of site conditions across locations. AR-enhanced video conveys the “on-site context” more effectively than text or still photos alone, accelerating decision-making.

In this way, AR and RTK visualization act as tools that extend inspection staff’s “eyes and brains.” In infrastructure sectors, practical use of AI-based automated diagnosis and AR-enabled visual inspections is beginning to be expected and, in some cases, field trials are already underway. AR-powered inspections bring digital objectivity and efficiency to areas that previously relied on human experience and intuition.

Advanced maintenance through 3D point-cloud scanning, cloud services, and digital ledger integration

While AR and RTK can streamline fieldwork, the preparation and use of robust underlying data are equally important. Key technologies for this are 3D point-cloud scanning, cloud data management, and integration with existing digital ledger systems. Combining these technologies can significantly enhance maintenance of common utility ducts.

First, about 3D point-cloud scanning. Recently, it has become easy to acquire 3D point-cloud data using LiDAR sensors built into smartphones and tablets or via photogrammetry using high-quality cameras. Point clouds are collections of many points that represent the shape of objects in space in detail. A worker can record surrounding structures as a 3D model simply by walking around with a smartphone and scanning exposed sections of buried infrastructure or the interior of handholes.

Using point-cloud data for utility duct maintenance enables more precise grasp of current conditions. For example, scanning exposed cables and conduits during construction or repairs creates a digital “replica” of buried assets. Even after backfilling, displaying the saved point cloud via AR lets users restore the original positions and shapes as if viewing through the ground. This directly supports non-destructive confirmation of buried assets and accurately guides future excavation.

Point clouds are not only shape records but can also be used for change detection. By scanning the same location during periodic inspections, differences such as crack propagation or deformation can be identified by comparing past and present point clouds. Even subtle displacements that are difficult to notice with the eye appear as differences when point clouds are overlaid. In the future, AI could analyze point-cloud data and automatically detect early signs of deterioration.

Next is cloud integration. Field-acquired point clouds, positioning data, photos, and notes can be uploaded to cloud servers via mobile networks. Using web-based GIS or 3D viewers hosted in the cloud, office staff can view and analyze site point clouds and positioning information nearly in real time on their PCs. This enables seamless information sharing between field and office. For example, a field worker pressing a sync button in the LRTK app can upload positioning results and photos to the cloud, allowing office engineers to review and provide instructions—establishing a rapid response workflow. Accumulated cloud data also promotes organizational knowledge sharing, helping to shift maintenance from a person-dependent practice to a data-driven one.

Equally important is integration with existing digital ledgers and other systems. Infrastructure management typically organizes information in GIS or dedicated asset-management ledgers. If AR inspection tools can exchange data with those systems, it becomes easy to retrieve and update ledger information on site. For instance, CAD drawings or GIS data uploaded to the cloud can be imported into an AR app for overlay on the field view. If DWG-format drawings created at design time are uploaded to the cloud, their cable routes can be projected via AR at the site. Conversely, newly measured or discovered positional information captured in the field can be fed back into ledger data and update the cloud database.

This bidirectional data linkage resolves discrepancies between ledgers and field conditions and enables maintenance based on up-to-date information.

By implementing point-cloud scanning, cloud services, and ledger integration, maintenance of common utility ducts can begin to realize a digital twin: a digital model that stays synchronized with the physical infrastructure, supporting everything from condition monitoring to preventive maintenance in a unified digital workflow. This is the DX (digital transformation) of the infrastructure sector, strongly supporting life-extension planning and asset management.

Simple inspection tools for anyone: smartphone + RTK device

To maximize the benefits of AR visualization and 3D data, the tools must be easy to use in the field. In the past, high-precision positioning and 3D scanning required specialized surveying instruments and expertise. But today, the combination of a smartphone and a compact RTK device is making it possible for each field worker to carry advanced positioning and inspection tools.

For example, our RTK solution uses a pocket-sized RTK-GNSS receiver that attaches to a smartphone and a dedicated app, turning the phone into a centimeter-accurate, multipurpose surveying instrument. By attaching a small device weighing only a few hundred grams, network-based RTK positioning can start without complex setup, allowing anyone to easily perform high-precision positioning in a global coordinate system or single-point measurements. The system also integrates with the phone’s camera and LiDAR to perform point-cloud measurements, AR-guided positioning and layout marking, and other functions—all with a single device. Data obtained can be shared to the cloud on the spot, smoothing data transfer between the field and the office.

Here are several advantages of a smartphone + RTK simple inspection tool:

• Portability and responsiveness: The tool is compact and lightweight, making it easy for workers to carry and use whenever needed. Inspections can start at a moment’s notice, enabling agile site rounds without prepping large equipment.

• Ease of learning: With a user-friendly smartphone app UI, no specialized surveying skills are required. Measurements and inspections proceed by following intuitive taps and on-screen guides, allowing even new staff to become productive quickly. Combined with AR visual feedback, this helps achieve standardized inspections not reliant on intuition or experience.

• Labor savings and efficiency: Tasks that once required two-person surveying teams (for example, one person holding a prism while another operates a transit) can now be completed by a single worker using a smartphone and RTK receiver. A single tap can record and share measurements, reducing post-processing and reporting workload. This allows limited staff to cover more inspection points.

• Added value through multifunctionality: A single smartphone can handle positioning, AR display, photography, point-cloud scanning, and distance/area calculations, so field teams can capture the data they need on the spot. If a worker wants to measure the depth of a cable or estimate the volume of a void, the app can perform those tasks immediately, enriching the evidence used for on-site decisions.

• Safety and comfort: Lightweight equipment reduces physical strain during long patrols. AR can display hazardous areas in advance or show guided routes to prevent workers from accidentally entering dangerous zones. In dark or adverse weather, AR markers provide reliable reference points that increase work accuracy and safety.

Thus, smartphone + RTK simple inspection tools realize “high precision, anywhere, by anyone,” transforming field operations. As unit prices become realistic for one-per-worker deployment, organizational DX accelerates. Tasks that once depended on skilled personnel become standardized through tools, enabling maintenance systems less reliant on individuals. Moreover, such digital tools help broaden participation in field work by younger staff and women, contributing to solutions for future labor shortages.

Promoting buried asset management DX with LRTK: integrating records, AR, and surveying

The AR-based subsurface visualization, high-precision RTK positioning, 3D point-cloud usage, and cloud integration discussed in this article are not futuristic fantasies—they are being integrated now into practical tools for the field. Our offering, “LRTK,” exemplifies such a tool that brings innovation to buried asset management.

LRTK is a system composed of a dedicated RTK-GNSS receiver that attaches to a smartphone and a companion app, delivering the following one-stop capabilities:

• Centimeter-level positioning and recording: With one-touch operation, users can measure their current position and record latitude, longitude, and elevation with centimeter accuracy. Measured points are automatically plotted on a map and stored with timestamps and notes. Registering duct equipment and surface structures in a ledger becomes drastically simpler.

• 3D point-cloud scanning: By walking around while using the phone’s camera, users can acquire 3D point-cloud data with absolute coordinates. Since LRTK continuously maintains high-precision self-positioning, scans remain undistorted and anyone can produce precise 3D records. Captured point clouds can be viewed and measured in the cloud and exported to CAD software as needed.

• AR projection of buried assets: The LRTK app can overlay pre-registered 3D models and measurement data onto live camera views at the site. For example, a point-cloud model of underground pipes scanned during test excavation can be recalled and AR-projected on the site after backfilling to accurately recreate the buried route. No tedious alignment is needed—RTK-based high-precision coordinates automatically place the model correctly.

• Surveying support (staking and guidance): LRTK includes a coordinate navigation feature that guides users to specified points based on coordinates or design alignments input from plans. Arrows and distance indicators on the smartphone screen guide the user to the target location, making staking and marking for new construction or excavation easy without waiting for a surveying crew.

• Cloud management of photos and notes: LRTK supports geotagged photo capture, and photos are linked in the cloud to point clouds and maps. For example, photos of deterioration inside a duct are saved with the shooting location’s coordinates and can later be viewed intuitively on a map or 3D viewer. This automates organization that is difficult with paper reports and speeds retrieval of past inspection records.

Having all these functions integrated in a single LRTK platform is a major advantage. With just a smartphone and an LRTK device, teams can perform surveying, inspection, recording, and sharing end-to-end, lowering the barrier to field IT adoption. LRTK is thus a practical tool for “streamlining maintenance of common utility ducts with AR.”

Infrastructure like common utility ducts is a long-lived asset expected to be used for decades. Improving and advancing their maintenance directly contributes to safety and cost reduction. Introducing digital technologies such as AR and RTK to streamline and enhance inspection work makes it possible to maintain infrastructure in good condition with limited personnel. Moreover, the high-precision data accumulated daily will become a valuable asset for future repairs and renewal planning.

As you begin to pursue DX in maintenance of common utility ducts, consider first adopting an AR + RTK solution that can be used on site. By using LRTK, you can digitalize everything from recording buried assets to visual inspection and surveying in one integrated workflow and smartly transform field operations. Making the invisible infrastructure “visible” is an excellent opportunity to update practices that relied on experienced intuition to data-driven methods. By incorporating the latest technologies into maintenance of this vital infrastructure, we can help realize a safer, more efficient pole-free society.