Improving Maintenance of Shared Underground Utility Ducts with AR: Visualizing Buried Facilities to Streamline Inspections

In recent years, initiatives to remove utility poles and place power lines and communication cables underground—known as pole-free urbanization—have advanced to improve cityscapes and strengthen disaster resilience. At the core of this infrastructure is the “shared underground duct for utility cables” installed beneath roads. These shared ducts are unseen civil-engineering assets that support urban life, but their maintenance requires continuous inspection and thoughtful practices. This article explains the structure and importance of shared underground ducts, summarizes the challenges facing current inspection operations, and explores a new solution that visualizes underground facilities above ground using AR (augmented reality) and RTK positioning to reduce inspection labor. It also introduces how 3D point-cloud scanning, cloud services, and integration with digital ledgers can enhance maintenance, and the significance of an easy inspection tool anyone can use by combining a smartphone with an RTK device. Finally, using our “LRTK” as an example, we present an integrated, innovative method that combines buried-asset recording, AR utilization, and surveying, and propose its adoption.

What is a shared underground duct: structure and role of an important infrastructure hidden underground

Shared underground duct for utility cables refers to an underground structure—typically concrete conduits beneath roads—designed to house multiple lifelines such as power cables and communication cables together. By consolidating infrastructure that would otherwise be buried separately into a single location, power and communications can be delivered safely and efficiently without utility poles or overhead lines. In urban areas, pole-free initiatives are being promoted for improved aesthetics and disaster resilience, and the development of shared underground ducts supporting this is progressing. With overhead lines gone from the surface, streetscapes become cleaner and pedestrian spaces expand, while urban safety is enhanced through reduced outage risk from strong winds or fallen trees. A shared underground duct is not merely a box for cables; it is a critical infrastructure that underpins urban functionality and safety.

The structure of a shared underground 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 underground space that houses multiple power and communication lines together. The handhole section is an opening to the surface placed at regular intervals along the conduit, providing space for workers to descend for inspection and repair. This configuration allows access to underground facilities without excavating the surface and enables efficient consolidated maintenance of multiple operators’ equipment.

In practice, the introduction of shared ducts significantly reduces the effort required for maintenance inspections and repair work, and offers many advantages such as the ability to inspect and restore cables quickly from a dedicated space during disasters.

That said, installing a shared duct is not the end; regular inspections are required to operate it safely over the long term. Laws regarding shared ducts and guidelines from road managers mandate periodic checks of structural integrity every few years, with repairs performed as needed. Keeping underground shared ducts, which operate out of sight, in good condition at all times contributes to citizens’ peace of mind and safety. Therefore, maintenance of shared underground ducts is an important challenge in urban infrastructure management.

Inspection work for shared underground ducts: current methods and challenges faced

Currently, inspections of shared underground ducts are mainly performed by people’s eyes and hands. Typically, a worker opens the lid of a handhole (inspection opening) placed by the roadside or on sidewalks and descends to carry out visual inspections. Large shared ducts have walkways that allow personnel to enter, while small conduits may be inspected by inserting cameras or fiberscopes. Inspections check items such as whether the concrete structure has cracks or leaks, whether cables are damaged or abnormally hot, and whether drainage equipment is functioning. Attention is also paid to interference points with other buried utilities such as gas and water/sewer pipes. Inspection results are recorded via photographs and logbooks, and repair plans are drawn up as necessary.

However, traditional inspection methods face several challenges. The first is the issue of workload and time. Because people must enter the underground space to inspect, inspections require a multi-person team, including safety monitors, increasing labor needs. Since work is performed on roads, preparations for traffic restrictions and the opening and closing of heavy manhole covers are required, and inspections at a single location can take a long time. Shared ducts extend long distances in urban areas, so inspecting the entire length regularly requires substantial man-hours; with current concerns about staffing shortages, this workload is heavy.

The second issue is the limit of visibility. Inspections that rely on flashlights or floodlights and human eyesight inevitably carry the risk of overlooking problems. Detecting abnormalities in deep parts of the conduit, high or blind-spot areas relies heavily on experience and intuition, and quality can vary when experienced personnel are lacking. It is also not easy to grasp the condition of the entire extensive duct network, so inspections are often forced to make judgments based on partial information.

Inefficient information management is another problem. Data obtained from inspections (photos and measurement results) are compiled into paper ledgers or reports, and comparing with past inspection records or instantly cross-referencing data from multiple locations is not always possible. Sharing information between departments can take time, and correcting or reflecting discrepancies between drawings and actual site conditions on the spot is difficult. In older shared ducts, original construction drawings may remain on paper and differ from actual conditions. Such analog management can hinder rapid decision-making and planned maintenance.

Finally, safety cannot be overlooked. Entering underground spaces carries risks of oxygen deficiency and toxic gases, requiring careful preparation and precautions. Opening lids and workers moving in and out on roads is itself a hazardous activity that requires alerting drivers and pedestrians. The more frequently inspections are performed, the more exposure to such risks increases.

As described above, current inspection operations for shared underground ducts are labor- and time-intensive, heavily dependent on individual skills, and carry safety challenges. A promising means to resolve or mitigate these issues is the use of AR technology and high-precision positioning (RTK). The next section examines in detail efforts to use AR to visualize buried facilities from the surface and guide inspection work.

Visualizing buried facilities with AR and RTK: inspection navigation by above-ground “see-through” visualization

If cables and conduits sleeping deep underground could be visualized on site without special imaging equipment, inspection work would be dramatically streamlined.

This is made possible by combining AR (augmented reality) and RTK-GNSS positioning. AR technology allows digital information to be displayed overlaid on the real-world view through a smartphone or tablet screen. For shared ducts, if pre-acquired location data or 3D models of underground structures are displayed in AR, workers on the surface can intuitively visualize what facilities run beneath the road and where they are located.

However, accurately aligning AR overlays requires precise knowledge of the device’s position and orientation. This is where RTK (Real Time Kinematic) high-precision GNSS positioning technology plays an important role. Standard GPS can have errors of several meters (several ft), but RTK uses correction information from a base station to improve positioning accuracy to a few centimeters (a few in). By attaching a compact RTK-capable GNSS receiver to a smartphone or tablet, current location can be measured to the centimeter level (cm level accuracy (half-inch accuracy)), enabling AR content to be aligned precisely with the real world.

This AR + RTK “above-ground visualization of buried facilities” offers various advantages for navigating inspection work.

• Quick location identification: For example, if the location of a handhole or underground facility to be inspected is unknown, an AR display can mark that spot on the ground so it can be identified at a glance. There is no need to carry drawings and use surveying instruments to set out positions; simply pointing a smartphone at the site will indicate “this is the lid to open next.” Digital markers can prevent misses even at night or in poor visibility.

• Shared underground-structure imagery: AR visually recreates the “underground piping image” that exists in the head of a veteran worker on the spot. Less experienced workers can grasp the layout of conduits and the spatial relationship with other buried utilities by looking at AR visuals. By making the invisible visible, AR aligns the entire team’s understanding and supports accurate decision-making.

• Guided inspection items: If linked to a digital ledger containing inspection items and past repair histories, AR can pop up information such as “this section was repaired last time” or “anomaly sensor present here.” In effect, AR can display a checklist to support comprehensive inspections. Even without experienced staff, AR can provide instructions, supporting standardized inspections.

• Non-destructive verification of buried assets: If the location information of buried assets acquired in advance is accurate, AR reproductions allow location confirmation without trial excavation. Combined with the 3D scanning technologies discussed later, one can, for example, accurately reconstruct in AR “the depth and burial of a previously repaired cable” and assess interference with other works above it. Reducing unnecessary excavations saves work time and cost.

• Recording and remote sharing: AR views can be saved as screenshots or videos. Annotating concerning areas while recording and sharing that data via the cloud with office specialists makes it easy to simultaneously confirm and discuss conditions on-site and remotely. AR video conveys the “sense of the site” better than text or still images alone, speeding up decision-making.

In this way, AR and RTK visualization extend inspectors’ “eyes and brains.” In the infrastructure sector, practical application of AI-based automatic diagnosis and AR visualization inspections is beginning to be expected, and field demonstrations are already underway in some areas. AR-enabled inspections are bringing digital objectivity and efficiency to tasks that previously relied on human experience and intuition.

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

While AR and RTK improve field efficiency, data preparation and utilization underpinning these functions are equally important. Key technologies here are 3D point-cloud scanning, cloud data management, and integration with existing digital ledger systems. Combining these enables a significant step-up in shared duct maintenance.

First, about 3D point-cloud scanning. Recently, using LiDAR sensors built into smartphones/tablets or high-performance cameras for photogrammetry, obtaining 3D point-cloud data of the site has become easy. Point-cloud data is a collection of numerous points that represent the shape of objects in space in detail. A worker can simply hold a smartphone and move around exposed sections or inside handholes to record surrounding structures as a 3D model.

Using point-cloud data in shared duct maintenance allows more precise current-condition understanding. For example, during construction or repair, scanning exposed cables and conduits captures their layout as a point cloud, preserving a digital “copy of the buried asset.” Even after backfilling, displaying the saved point-cloud data in AR can restore the original positions and shapes as if透視している, guiding future excavation work accurately. This directly supports non-destructive confirmation of buried assets mentioned earlier.

Point clouds are also useful for detecting changes. If the same location is scanned at each inspection, comparing current and past point clouds can reveal crack progression or deformation. Micro-displacements that are difficult to detect by eye can emerge as differences when point clouds are overlaid. In the future, AI could analyze point-cloud data to automatically detect signs of deterioration.

Next is cloud integration. Point clouds, positioning data, photos, and notes captured on site can be uploaded to cloud servers via mobile networks. With web GIS and 3D viewers on the cloud, office PCs can view and analyze field point clouds and position data almost in real time. This creates seamless information sharing between field and office. For example, when a field worker taps a sync button in the LRTK app, positioning results and photos are uploaded to the cloud, enabling office engineers to review and respond—establishing a rapid response system. Accumulating data in the cloud facilitates organizational knowledge sharing and moves maintenance from being person-dependent to data-driven.

Equally important is linking with existing digital ledgers and other systems. In infrastructure management including shared ducts, information is often organized in GIS or dedicated asset management ledgers. If an AR inspection tool can interoperate with these systems, calling up and updating ledger information on site becomes easy. Practically, CAD drawings or GIS data can be imported into an AR app from the cloud and overlaid on site. For instance, DWG-format drawings created during the design phase can be uploaded to the cloud and AR-projected on site to verify cable routes. Conversely, newly measured position data discovered on site can be fed back into ledger data to update the cloud DB.

This bidirectional data linkage resolves discrepancies between ledgers and actual conditions, enabling maintenance based on always-up-to-date information.

By implementing point-cloud scanning, cloud services, and ledger integration as described, maintenance of shared ducts moves toward digital twin realization—where real-world infrastructure and its digital model are synchronized, supporting everything from condition monitoring to preventive maintenance in a unified digital workflow. This is a form of DX (digital transformation) in the infrastructure field and strongly supports long-life planning and asset management.

Easy inspection tools with smartphone + RTK devices for anyone to use

To maximize the benefits of AR visualization and 3D data utilization, the tools must be easy to use in the field. Historically, high-precision positioning and 3D scanning required specialized surveying equipment and expert knowledge. Today, however, 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 plus a dedicated app to turn the phone into a versatile surveying instrument with centimeter-level accuracy (cm level accuracy (half-inch accuracy)). Simply attaching the small device, which weighs only a few hundred grams, enables RTK positioning via network without complex setup, and anyone can easily perform high-accuracy positioning in a global coordinate system and single-point measurements. Integrated smartphone cameras and LiDAR can be used for point-cloud measurements, and AR-based positioning guidance or stakeout can be done on the screen—allowing one device to handle many functions. Captured data can be shared to the cloud on the spot, smoothing data transfer between field and office.

Here are several benefits that smartphone + RTK easy inspection tools bring:

• Portability and responsiveness: The tool is small and lightweight enough to fit in a pocket, so workers can carry it and use it whenever needed. Positioning and AR display can start immediately, enabling nimble site inspection without assembling bulky equipment.

• Ease of learning: The intuitive UI of a smartphone app allows operation without specialized surveying skills. Measurements and inspections proceed by simple taps and on-screen guidance, so new staff can become productive quickly. Visual AR feedback also supports standardization that does not rely on intuition or experience.

• Labor reduction and efficiency: Tasks that traditionally required two people for surveying (e.g., one holding a prism and another looking through a transit) can be completed by a single person with a smartphone and RTK receiver. A single tap records and shares data automatically, reducing post-processing and reporting work. This enables limited staffs to cover more inspection points.

• Added value through multifunctionality: One smartphone can measure positions, display AR, take photos, scan point clouds, and calculate distances and areas—providing the data needed on demand. For example, if you want to measure a cable depth or estimate the volume of a cavity, you can do it immediately in the app. Observations made during inspections can be digitized on the spot, enriching decision-making materials.

• Safety and comfort: Lightweight equipment reduces physical burden during long patrols. AR can pre-display hazards or indicate guided routes to prevent workers from entering dangerous areas accidentally. AR markers are reliable in dark or poor weather, improving work accuracy and safety.

Thus, smartphone + RTK easy inspection tools realize “high accuracy for anyone, anywhere,” transforming field operations. With realistic per-person device deployment becoming affordable, organizational DX accelerates. Tasks that relied on experienced personnel can be leveled by tools, moving maintenance toward a less person-dependent system. Use of such digital tools also helps diversify the workforce—encouraging participation by younger staff and women—and contributes to addressing future labor shortages.

Promoting buried-asset management DX with LRTK: integrating recording, AR use, and surveying

The enabling technologies discussed in this article—AR visualization of underground facilities, high-precision RTK positioning, 3D point-cloud data utilization, and cloud integration—are not science fiction; they are already being integrated into practical field solutions. Our offering, “LRTK,” exemplifies a tool that brings innovation to buried-asset management.

LRTK is a system consisting of a dedicated RTK-GNSS receiver that mounts to a smartphone and an app, delivering the following functions in one stop:

• Centimeter-class positioning and recording: With one-touch operation, current position is measured and latitude, longitude, and elevation are recorded with centimeter-level accuracy (cm level accuracy (half-inch accuracy)). Measured points are automatically plotted on maps and stored with timestamps and notes. Registering duct internal equipment and surface structures into ledgers becomes dramatically simpler.

• 3D point-cloud scanning: By walking around with the phone camera, users can acquire 3D point-cloud data with absolute coordinates. Because LRTK continuously maintains high-precision self-positioning, scans remain undistorted and anyone can create precise 3D records. Acquired 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 site imagery. For example, calling up a point-cloud model of underground pipes scanned during trial excavation and AR-projecting it after backfilling accurately restores the buried route on site. No tedious alignment is required; RTK-based high-precision coordinates automatically place the model in the correct location.

• Surveying support (stakeout and guidance): LRTK includes a coordinate navigation feature that guides users to specified points based on coordinates or lines input from design drawings. Arrows and distances are shown on the smartphone screen to lead users to target positions. This makes it easy to mark stakeout points for new works or excavation locations without waiting for a surveying team.

• Cloud management of photos and notes: LRTK supports geotagged photo capture, and photos are linked in the cloud with point clouds and maps. For example, photographing deterioration inside a shared duct saves the image with its capture coordinates so you can intuitively see “what photo was taken where” on a map or 3D view. This automates information organization that is difficult with paper reports and speeds retrieval of past inspection histories.

Having all these functions integrated in a single platform—LRTK—is a major advantage. With just a smartphone and an LRTK device, surveying, inspection, recording, and sharing can be performed end-to-end, lowering the IT adoption barrier at sites. It is a practical tool to “improve maintenance of shared underground ducts with AR.”

Social infrastructure such as shared underground ducts are long-lived assets used for decades once installed. Improving and advancing their maintenance directly ties to infrastructure safety and cost reduction. Introducing digital technologies like AR and RTK for labor-saving and advanced inspections makes it possible to keep infrastructure in good condition with limited personnel. High-precision data accumulated daily also becomes a valuable asset for future refurbishment and renewal planning.

As you move forward with DX for shared underground duct maintenance, why not start by introducing an AR + RTK solution that is usable in the field? By utilizing LRTK, you can digitize everything from buried-asset recording to visual inspection and surveying in a single workflow, smartly transforming field operations. This is a prime opportunity to update work that relied on veteran intuition into data-driven practices by making invisible infrastructure “visible.” Incorporating the latest technologies into maintenance of crucial infrastructure like shared underground ducts will support the realization of a safe and efficient pole-free society.