Table of Contents

• Introduction

• Current Situation and Challenges of Buried Utility Damage Incidents

• Conventional Methods for Confirming Buried Utilities and Their Issues

• Visualizing Drawings, Boundaries, and Buried Utilities On-Site with AR

• Benefits of Displaying Drawings, Boundaries, and Buried Utilities in AR

• High-Precision AR Display Achieved with RTK-GNSS

• AR Use at Excavation Sites: Visualizing Boundaries and Buried Utilities

• Easy High-Precision AR Introduction with Simple Surveying Using LRTK

• FAQ

Introduction

Excavation work in construction always carries the risk of inadvertently damaging pipes and cables buried underground. For example, if a backhoe (hydraulic excavator) severs a gas pipe or power cable while digging, it can lead to gas leaks or large-scale power outages. In fact, incidents of damage to underground buried utilities have continued to occur in recent years, causing serious problems such as impacts on nearby residents, high restoration costs, and safety concerns.

To prevent such excavation accidents, meticulous prior checks and vigilance are indispensable. If the positions of buried utilities can be accurately identified and the “invisible made visible,” everyone can work with confidence. A recently notable approach is to utilize AR (augmented reality) technology to visualize underground buried utilities and boundary lines in advance. This article explains how on-site AR display of drawings, boundaries, and buried utilities contributes to accident prevention, considering the current situation of buried utility damage incidents and the challenges of conventional measures. We also introduce the latest technologies that make high-precision AR easy to realize and our simple surveying system LRTK, offering tips to aim for zero excavation accidents.

Current Situation and Challenges of Buried Utility Damage Incidents

At roadworks and land development sites, unseen underground infrastructure is always a latent hazard. In Japan, more than 100 cases of underground buried utility damage incidents are reported annually, and some years see roughly 150 cases. The main damaged targets include potable water pipes, sewer pipes, communication cables, power lines, and gas pipes. Damage to water pipes accounts for a large proportion in some years—about half. Although the number of gas pipe break incidents is not high, once they occur they pose a high risk of gas leakage or fire to the surrounding area and always carry the potential to become a major incident.

Behind these buried utility damage incidents are cited issues such as insufficient underground detection and prior checks and miscommunication of information. There are cases where excavation operators or construction managers assume “there should be no buried utilities here” and operate heavy equipment, resulting in accidentally cutting an overlooked cable. It is also possible that the actual buried position differs from what is recorded on the drawings, even where the drawings appear to indicate a safe location. Small differences in awareness or complacency can lead to major accidents, and construction sites are constantly alerted to this risk. Once an accident occurs, delays in the construction schedule and impacts on the surrounding area are unavoidable, and contractors face loss of social trust and the risk of compensation claims.

Achieving “zero accidents” requires measures to eradicate buried utility damage incidents. This means thoroughly enforcing conventional safety measures (such as prior confirmation of buried utility locations, exploratory hand-digging, and third-party attendance) while also employing the latest technologies to improve the accuracy and reliability of confirmation work.

Conventional Methods for Confirming Buried Utilities and Their Problems

To prevent accidents, various confirmation tasks have traditionally been carried out on site. Before beginning excavation, teams typically obtain various burial drawings (such as buried pipeline maps and utility owners’ piping diagrams) to grasp what is buried underground. If necessary, they also use buried-utility detection equipment such as ground-penetrating radar or cable locators to investigate the actual positions of pipes and cables beneath the surface. When important gas lines or communication cables are present, it is common to request the utility owner’s representative (from gas or communications companies) to attend and jointly confirm positions on site. Confirmed utility routes are often visualized for the heavy equipment operator by marking the ground with spray paint, driving stakes, or placing signs.

However, several problems have been pointed out with these conventional methods. First is the uncertainty of drawing information. Paper drawings and design plans do not always accurately reflect the current situation. Older infrastructure often shows discrepancies between recorded drawings and actual buried positions, and records may not have been updated after renovation work. There are cases where excavation performed based on drawings judged safe uncovers unexpected cables. Second is the difficulty of pinpointing positions on site. Even if coordinates or distances are written numerically on a drawing, accurately measuring those on an outdoor site requires surveying knowledge and effort. For those without experience, translating drawing information to an exact point on the ground is not easy, and decisions often end up relying on experienced-based intuition.

In addition, detection equipment is not omnipotent. Targets that are hard to detect include pipes under concrete or deep-buried plastic pipes that detection devices struggle to find. Completely identifying all buried utilities in advance requires significant time and effort and is sometimes impractical. Coordinating third-party attendance and carrying out marking work also take time. If human error or communication gaps occur, markings may not be shared with workers and the accident risk remains. Thus, conventional methods alone have limits in confirming buried utilities, and more intuitive and reliable support measures have been sought.

Visualizing Drawings, Boundaries, and Buried Utilities On-Site with AR

A new approach that has emerged is the use of AR (augmented reality) technology. AR overlays CG and text information onto smartphone or tablet camera images. Using AR makes it possible to display design lines, boundary lines, and the positions of underground buried utilities—previously only confirmable on paper drawings—overlaid onto the actual site as AR displays. For example, when viewing the site through a tablet screen, virtual lines and markers can appear on the ground. It is as if wearing X-ray glasses to peer underground: the routes of pipes buried beneath the surface and site boundary lines seem to float over the real world.

The key point of AR display is that it provides visual information that workers can intuitively understand. There is no need to mentally interpret drawings and map them to the site; simply pointing a phone reveals information such as “a gas pipe runs ahead from here” or “you may only dig up to this line.” Tasks that used to rely on veteran intuition can, with AR, be visually judged by anyone. Even inexperienced operators can operate heavy machinery within safe limits by following virtual guide lines shown on the screen.

AR also offers the advantage of real-time information sharing. If multiple people view the AR display on site, managers and operators can share the same image. Headquarters staff or design personnel located remotely can receive photos or videos of the AR display and understand the situation or give instructions without visiting the site. In this way, visualization with AR not only makes information easier to see but also serves as a powerful communication tool on site.

Benefits of Displaying Drawings, Boundaries, and Buried Utilities in AR

Using AR to visualize drawing information, boundary lines, and buried utility positions brings many benefits, including:

• Improved work efficiency: The need to repeatedly compare paper drawings and actual site conditions is eliminated; required information can be understood by simply holding up a device. By substituting some stake placement and surveying point checks with AR, the time spent on surveying and checks is greatly reduced. As a result, preparatory work becomes more efficient and construction schedules can be shortened.

• Improved safety and reliability: Because AR can accurately indicate dangerous areas and important buried utilities, the risk of accidental damage by heavy equipment can be reduced. With all workers paying attention to the same locations, incidents of “digging without knowing” are prevented. Measurements in high or confined spaces can also be confirmed from a safe distance via AR display, eliminating the need for workers to assume dangerous postures.

• Smooth communication: Shared visual information via AR helps site staff, designers, and supervisors hold a common image. Truly, “seeing is believing”: complex design intent that is hard to convey on paper drawings can be understood at a glance. This makes meetings and instructions smoother and reduces mistakes from misalignment of recognition.

• Promotion of DX and contribution to skill transfer: Using familiar technologies like smartphones and AR, advanced surveying and confirmation work becomes possible even without expert surveyors. This is a helpful tool for labor-saving and labor-reduction at construction sites suffering from severe manpower shortages. It also aligns with site digitization initiatives (ICT construction and *i-Construction*), and as an intuitive technology that young workers readily accept, it contributes to skill transfer. A reproducible method that does not rely on veteran “intuition and experience” could become a future standard.

Thus, on-site visualization using AR is a groundbreaking solution that positively impacts quality, efficiency, and safety. In excavation work especially, it is undeniably a major asset in accident prevention.

High-Precision AR Display Achieved with RTK-GNSS

That said, ensuring accuracy is crucial to make AR practical on-site. GPS built into ordinary smartphones or tablets can sometimes have errors of several meters. Displaying underground utilities with that level of error would not be usable for safety confirmation if the displayed position deviates from the actual pipe by meters. Conventional AR apps align by recognizing planes in camera images or using artificial markers, but as users walk around, displays can gradually drift. In wide outdoor sites with few reference points, it is difficult to keep virtual models correctly positioned for long with ordinary GPS accuracy. For these reasons, AR has so far been a rough visualization tool and has been difficult to apply to surveying or layout tasks that require millimeter- or centimeter-level precision.

The trump card to solve this issue is combining RTK-GNSS positioning with AR display. The RTK (real-time kinematic) GNSS positioning method uses correction information from a base station to dramatically improve positioning accuracy. By attaching a dedicated high-precision GNSS receiver to a smartphone or tablet and receiving correction data delivered over the network or augmentation services such as Japan’s quasi-zenith satellite “Michibiki” centimeter-class augmentation service (CLAS), a smartphone can determine its position with an error of about 1–2 cm (0.4–0.8 in). This level of precision is orders of magnitude better than the several-meter accuracy typical of ordinary GPS, and it can be achieved with palm-sized equipment.

If a smartphone can obtain accurate coordinates in the global geodetic system, it becomes possible to directly link pipeline routes shown on design drawings or GIS data with the real-world site. In other words, digital coordinates and physical site coordinates can be handled with a common reference. By linking coordinate information embedded in design data with the device position and orientation obtained via RTK-GNSS on site, virtual objects (for example, buried pipe models or design lines) can be displayed precisely overlaid on their correct real-world positions.

With high-precision GNSS-based AR, once alignment is performed, virtual models remain fixed to the correct place even as the user moves. Without complex initial calibration or marker placement, simply pointing a device yields AR that automatically appears at the correct positions. This “no coordinate-alignment-needed” AR experience, difficult with ordinary GPS, gives the sensation that points and lines on the design drawing materialize directly at the site. For example, even at night or in bad weather, trusting the line shown on the device allows confident excavation to the correct position. It is precisely this centimeter-level accuracy (cm level accuracy (half-inch accuracy)) in AR display that can fundamentally reduce the risk of damaging buried utilities and make AR a reliable tool.

AR Use at Excavation Sites: Visualizing Boundaries and Buried Utilities

Now let’s look at typical use cases of AR at excavation sites. The key is to clearly indicate “where to dig” and “where to be cautious.”

First is using AR for boundary line marking of excavation areas. In open-cut excavation and similar work, the shape and depth of the planned excavation area are defined in the design drawings. Normally, this range is surveyed and staked or marked on the ground with spray, but AR can greatly reduce that labor. If you prepare 2D line data from the design drawings in advance, simply pointing a smartphone on site will display the planned excavation boundary lines virtually on the ground. Operators can control machinery while checking the lines on the screen and accurately excavate within the designated area even without physical stakes. For example, if a red line is displayed showing “do not dig beyond this boundary,” the limit is immediately clear and surrounding workers can share that line. Even inexperienced workers can complete tasks without hesitation by following the visual guide lines.

Next is visualization of buried utilities. If the route information of underground buried utilities (GIS data or CAD drawings) obtained in advance is loaded into the AR app, the camera view on site will project the routes of underground pipes and cables virtually onto the surface. For example, if a buried gas pipe crosses diagonally underfoot, a yellow virtual line or warning marker will be displayed along the ground above it. Workers can intuitively understand “a gas pipe runs under here” and can switch to hand digging with a shovel near that spot or use shallower bucket teeth on the heavy equipment to carefully remove soil. This can dramatically reduce the risk of hitting a pipe.

Until now, work on site often involved measuring straight-line distances on drawings, marking the ground, and then digging with caution around where utilities were “probably” buried. With AR, the actual routes of buried utilities appear directly, allowing workers to grasp distances precisely, such as “a pipe is within 1 m (3.3 ft) from here”. This provides great reassurance to operators. If an unknown buried object not shown on the drawing is exposed, the positional relationship with known buried utilities displayed around it helps rapid judgment—e.g., “this pipe is not on the new drawings, so it may be old.” Thus, AR not only presents existing information but also promotes on-site discovery.

By showing both excavation boundaries and buried utility locations simultaneously in AR, it becomes clear “how far to dig” and “what to avoid.” Construction managers can identify hazardous areas in advance and optimize work plans via AR, and safety briefings or KY activities can use actual AR images to alert workers. As a result, the entire site can share awareness and concrete measures toward zero accidents.

Easy High-Precision AR Introduction with Simple Surveying Using LRTK

As discussed, high-precision alignment is key to realizing on-site AR visualization of buried utilities. How can you easily obtain such high-precision location information on site? Traditionally, specialized surveying equipment and procedures were required to establish control points, but today centimeter-precision positioning is possible with just a smartphone. A representative example is our portable GNSS system, LRTK.

LRTK consists of a small high-precision GNSS receiver that can be attached to a smartphone or tablet and a dedicated app. Turning on the power and launching the app starts RTK positioning. The device is pocket-sized and lightweight, so you do not need to carry heavy tripods or fixed surveying instruments. It requires no complex initial setup: tap a button on the screen at the location you want to survey to record that moment’s latitude, longitude, and elevation. It is designed to be intuitive and operable without specialized knowledge, so both veterans and younger staff can use it easily.

Yet positioning accuracy is surprisingly high: by receiving RTK correction information, you can stably obtain accuracy within a few centimeters (within a few inches). There is no need to purchase a large dedicated device or set up a local base station, keeping initial costs lower than traditional high-precision surveying equipment. Furthermore, LRTK receivers support multiple satellite positioning systems (GPS, GLONASS, Galileo, etc.) as well as Japan’s satellites, allowing stable positioning even in mountainous areas with poor reception. Models compatible with Michibiki’s CLAS signal can acquire correction information directly from satellites even where mobile signals are unavailable, enabling high-precision positioning to continue in tunnels or remote mountains. The reliability of maintaining consistent accuracy across various sites is a great reassurance for site personnel.

By utilizing LRTK, anyone can easily obtain centimeter-precision location information, making the previously described high-precision AR visualization of buried utilities easy to introduce. For example, measure known reference points or building corners on site with LRTK and align them with the design coordinate system; thereafter, simply overlay the design data accurately on the smartphone screen. Tasks that used to take a skilled worker half a day to perform can be replicated quickly by anyone using LRTK and AR. As a result, AR displays for preventing buried utility accidents can be adopted as a new everyday practice on site. With no need for expensive dedicated equipment and the ability to measure whenever needed, LRTK truly represents a revolution in simple surveying. Actively utilizing such latest tools to raise safety standards on site is the fastest route to zero excavation accidents.

Finally, the fusion of AR visualization and high-precision positioning technology is becoming the standard on future construction sites. To protect lives and societal infrastructure, we should actively use technology and move forward toward the goal of “zero damage to buried utilities.”

FAQ

Q. Can AR really make buried utilities “visible”? A. AR is not magic, but by overlaying pre-prepared buried utility position data onto real-world images, it creates an experience that feels as if the underground is visible. For example, if you import gas pipe route information from drawings into an AR app, viewing the ground through a smartphone will show the pipe’s path as a line. You do not actually see the pipe itself underground, but because you can visually confirm “what is buried here,” you can make decisions at a level close to what you would with direct visual observation.

Q. What preparations and equipment are required to display buried utilities in AR? A. Basically, you need an AR-capable smartphone or tablet and digital data of the buried utilities or design drawings. Prepare the location information of pipes, cables, boundaries, etc. in GIS data or CAD formats and load them into a compatible AR app. The smartphone must accurately determine its current position and orientation, so it is recommended to use a high-precision GNSS receiver (such as a device like LRTK) in addition to the built-in GPS. AR itself works without high-precision GNSS, but display positions will be prone to error, making it unreliable for safety-critical uses. With a high-precision GNSS-equipped phone, prepared data will be accurately overlaid at the site, allowing confident use of AR displays.

Q. Is it okay to rely only on smartphone GPS and the electronic compass for alignment? A. For precise alignment, the accuracy of a standard smartphone GPS or compass is, frankly, insufficient. GPS errors of several meters are common, and compasses are easily affected by local magnetic environments; they are not suitable for indicating precise underground pipe positions. Therefore, for serious AR use on sites, it is realistic to use a smartphone-mounted high-precision GNSS unit. RTK positioning from high-precision GNSS enables position determination with centimeter-level error and provides high-precision orientation correction based on GNSS. Using such auxiliary devices ensures the virtual models on the smartphone always match actual positions and makes AR reliably usable for on-site decisions.

Q. If the drawing data is inaccurate, does that affect the AR display? A. Yes. AR simply displays the provided data, so if the original drawing information is wrong, the same error will be reproduced. For example, if a pipe is missing from the drawing, it will not appear in AR. This is an important consideration. However, adopting AR increases opportunities to discover such data deficiencies. When checking AR on site, if you sense a discrepancy—“a pipe that should be straight on the drawing seems to detour in reality”—you can re-investigate with detection equipment. In short, AR is not omnipotent but serves as a complementary tool that promotes human awareness. With accurate data, AR’s benefits are maximized; if data is deficient, AR helps detect issues early. In any case, preparing up-to-date drawing information and prior detection results is a precondition for effective AR use.

Q. Are you concerned that site workers may not be able to use it properly? Is special training required? A. AR app operation is very simple and intuitive. Basically, information is displayed automatically by pointing a smartphone or tablet camera. Those accustomed to smartphone cameras or map apps will have little trouble. A few hours of explanation or a simple demo at introduction is usually enough for most workers to use it on site the next day. Young workers often find it easier to understand than reading paper drawings. LRTK-type positioning devices are also easy to use—just power on and connect to the phone—and are designed to be operable without expert knowledge. On site, supervisors typically lead by example, and workers often adopt it naturally after seeing it used, a pattern of gradual, organic adoption.

Q. Is the cost of introducing AR and high-precision equipment really worth it? A. Preventing even one buried utility damage incident can justify the investment. Considering the costs of incident response and repair, losses from schedule delays, and damage to social trust, investing in accident prevention via AR is highly meaningful. Fortunately, recent high-precision GNSS devices and AR apps have become more affordable as they spread, and initial costs are relatively low compared to buying dedicated heavy machinery. When factoring in labor savings from improved efficiency and reduced errors, the overall cost-performance is high. Once data is prepared, it becomes an asset that can be reused at other sites and for future projects. AR use offers benefits in both safety and productivity and is becoming a next-generation standard method. Early adoption can lead to future competitive advantage. AR technology that transforms safety culture while improving efficiency will likely bring value beyond its cost.