Construction Techniques to Visualize Underground Utilities with AR: Preventing Mistakes, Improving Inspection Accuracy, and Ensuring Consensus

Table of Contents

• The significance of visualizing underground utilities with AR

• Preventing construction errors using AR technology

• Improving inspection accuracy through AR utilization

• Facilitating consensus building in construction with AR

• Technical elements that support high-precision AR

• Simple surveying for anyone with LRTK

• Summary

• FAQ

The significance of visualizing underground utilities with AR

In recent years, as social infrastructure ages, safely carrying out construction without damaging existing underground utilities and advancing infrastructure maintenance have become major challenges. On construction sites, accurately understanding the positions of underground utilities such as buried pipes and cables is critically important. Accidentally damaging a gas line or power cable can lead to serious incidents or construction delays. Traditionally, workers often had to estimate positions on site using drawings or mark the surface with stakes or spray paint; understanding invisible underground conditions required effort and experience. Those methods carry risks of markers shifting or being lost, so workers must always proceed with caution. Furthermore, the labor of exploratory excavation to confirm the locations of utilities beforehand can be reduced with AR. If drawings and AR data are accurate, it is possible to grasp the positional relationships of buried utilities without digging up the ground, allowing rationalization from the planning stage.

By leveraging AR (augmented reality) technology, structures under the ground can be visualized as if透視 through the camera. Pre-prepared digital data of underground utilities can be overlaid on the screen of a smartphone or tablet to realize the “visualization” of underground pipes and cables. This enables workers to directly and accurately understand underground conditions on site by sight, allowing them to work safely and efficiently. Visualizing underground utilities with AR is attracting attention as a new construction technique emblematic of DX (digital transformation) in construction sites. In short, efforts to make previously invisible things "visible" are becoming commonplace on job sites.

Preventing construction errors using AR technology

The most direct benefit of AR visualization of underground utilities is preventing construction-time mistakes. In particular during excavation work, being able to see what is buried under the ground at a glance greatly reduces the risk of accidentally damaging pipes or cables. For example, simply pointing a tablet’s camera at the ground can display buried gas pipes and sewer/water lines on the screen as color-coded lines. Workers can intuitively understand what is buried beneath the ground in front of them, carefully adjust excavation locations, and prevent contact accidents with critical lifelines. Repairing damaged utilities tends to be costly and can have broad impacts on the surrounding area, so preventing such incidents is essential. Visualizing hazardous locations in advance with AR allows all workers to share the points that require attention, contributing to an overall improvement in site safety awareness.

Furthermore, AR is effective not only for dealing with existing utilities but also for preventing installation errors of new structures. By overlaying a design 3D model onto the real scene via AR, the “correct position” where components should be installed is visually indicated. Workers can accurately confirm on site whether components are placed according to the design on AR, instantly detecting and correcting even slight misalignments. For example, in bridge work when installing piers or anchor bolts, overlaying the 3D model of the design position onto the real world enables addressing even deviations of a few centimeters (a few in) without overlooking them. Detecting and correcting mistakes on the spot prevents rework later, thereby improving overall construction quality and safety.

Improving inspection accuracy through AR utilization

AR technology also contributes to increased accuracy in inspection tasks for infrastructure facilities and structures. Normally, inspecting and confirming the state of underground utilities required comparing drawings with the site or, if necessary, digging up the ground for direct confirmation. With AR, you can accurately understand the locations of underground pipes and structures without such labor, dramatically streamlining supervision and inspection work. In addition, if inspection findings confirmed via AR are recorded directly as photos or videos, you can keep inspection records that are more intuitive and easier to understand than paper reports. For example, because you can confirm in real time on a tablet the separation (distance) between excavation points and buried pipes while proceeding with work, you can simplify on-site marking tasks that used to rely on stakes or paint, and inspectors will need to measure distances repeatedly less often. Constantly understanding the positional relationship between excavators and underground utilities on AR improves safety and construction certainty and is also effective for inspections.

AR also proves powerful in maintenance of existing infrastructure. For instance, when inspecting aging bridges or tunnels, overlaying past design drawings and records of deterioration onto the current condition via AR allows precise identification on site of areas that need repair. Similarly, for maintenance of underground pipes, previous survey data and records of burial positions can be visualized with AR so that the condition and layout of buried pipes can be understood from the surface. This makes it easier to intuitively detect overlooked deterioration or damage, dramatically improving inspection accuracy. AR-based inspections are transforming traditionally experience- and intuition-reliant work into data-driven smart tasks. Some sites have already begun using AR for as-built inspections by regulatory authorities, streamlining the matching of drawings with constructed elements.

Facilitating consensus building in construction with AR

AR visualization not only enhances safety management and quality but also facilitates smoother consensus building among stakeholders. For clients, nearby residents, and infrastructure managers who may lack technical knowledge, understanding underground conditions or the post-completion image from drawings alone is not easy. However, by holding a tablet on site and displaying the arrangement of buried utilities or planned structures in AR, anyone can intuitively understand the current situation and the plan. There is no need to spread multiple paper drawings for explanation; showing footage overlaid on the actual site makes comprehension easier.

For example, on sites where buried pipes are densely concentrated, explaining construction status using AR displays in the presence of the client enables them to instantly understand what countermeasures are being taken underground. Content that previously had to be explained with words or drawings can be conveyed without misunderstanding by sharing AR imagery and explaining on site. Walking around while projecting the completed image in AR also makes it easier to gain agreement in neighborhood briefings or meetings with owners. Sharing information in a visually tangible way helps resolve stakeholders’ anxieties and questions, smoothing overall project communication. AR becomes a powerful communication tool on site and accelerates consensus building. Also, during joint inspections with facility managers (for example, gas companies or water utilities), confirming buried conditions together in AR allows you to accurately convey the impact range of the work and provide reassurance.

Technical elements that support high-precision AR

To accurately visualize underground utilities with AR on construction sites, several technical points are important. First and foremost is alignment accuracy. AR displays that rely only on standard smartphone GPS or compass can produce misalignments on the order of a few meters (a few ft), which was insufficient for civil engineering construction management that requires precision. That’s where RTK (real-time kinematic) satellite positioning technology comes in. By combining an RTK-capable high-precision GNSS receiver with an AR device, you can determine your own position with centimeter-level accuracy—errors of a few centimeters (a few in)—allowing digital data overlays to align with minimal offset. In practice, systems have been commercialized where simply walking the site with a tablet fitted with a compact RTK-GNSS antenna displays design drawings and buried utility data perfectly aligned with the real world. Dramatically improving positioning accuracy in this way has made previously difficult, highly accurate AR displays possible. In environments where GNSS signals cannot reach, such as inside tunnels or under elevated structures, SLAM (Simultaneous Localization and Mapping) technologies that estimate device position by capturing surrounding feature points with cameras or LiDAR sensors are also used to complement AR display accuracy.

Equally indispensable is preparing the digital data of the underground utilities to be displayed in AR. Original design drawings, CAD data, and geographic information from GIS must be converted into 3D models and pre-aligned for AR. The spread of BIM/CIM in recent years has led to better-prepared 3D design and construction data, accelerating the trend of bringing these to sites for AR use. However, if the positional information of buried utilities is inaccurate or models are outdated, AR displays will not match reality. Therefore, it is important to grasp the actual positions of buried utilities through high-precision surveys and update data accordingly. Recently, tools have appeared that allow easy high-precision point-cloud surveying or photogrammetry on site and immediate reflection of that data in AR displays. Combining these technical elements is creating an environment where anyone can easily perform high-accuracy AR visualization. The Ministry of Land, Infrastructure, Transport and Tourism’s promotion of i-Construction also recommends using ICT and 3D data, and AR-driven construction DX is expected to spread further.

Simple surveying for anyone with LRTK

LRTK has emerged as a solution to readily realize high-precision AR-based construction visualization on site. LRTK is a system consisting of an ultra-compact RTK-GNSS receiver that attaches to the back of a smartphone and a dedicated app; its characteristic is that turning on the device immediately provides centimeter-level positioning accuracy. Unlike other AR surveying tools, there is no need to place markers in advance or perform cumbersome manual coordinate alignment. Attach a smartphone case containing the compact receiver (weighing about 125 g and thickness 13 mm (0.51 in)) with a single touch, and your everyday smartphone instantly becomes a high-precision positioning device. Because high-precision AR can be used without difficult initial setup, even non-specialist surveyors can operate it immediately on site.

With LRTK, acquired data is reflected in the device app via the cloud in real time, allowing design models and survey data to be shared on site instantly. Enabling anyone to easily obtain centimeter-accurate point-cloud data and AR displays directly leads to reduced construction errors and faster surveying work. In fact, reports indicate that using LRTK allowed one person per smart device to perform everything from simplified surveying to layout marking, inspection, photo recording, and even AR-based as-built simulation, dramatically improving on-site productivity. Also, sharing the completed image in AR while walking the site with clients and stakeholders makes on-the-spot discussion and confirmation possible, smoothing consensus building. LRTK is turning high-precision surveying and AR technologies, which once required specialists, into tools anyone can handle in the form of simple surveying.

Summary

The construction technique of visualizing hidden underground utilities with AR has clearly large effects on construction sites. From preventing human errors during excavation to improving construction quality and smoothing communication among stakeholders, it offers benefits across the board. Environmental benefits can also be expected, such as reducing waste from fewer construction mistakes and paperless workflows through digitized drawings. By overlaying digital data onto real space, site management that used to rely on the intuition and experience of veterans is shifting toward smart construction where anyone can make objective, data-based decisions. Using convenient, high-precision tools such as the recently introduced LRTK brings an era in which AR technology—once difficult to adopt—becomes commonplace on sites. A future where work proceeds while visualizing underground utilities with AR will dramatically improve both safety and productivity and become a new standard in the construction industry. Eventually, using AR glasses (wearable devices) to continuously display the positions of buried utilities in workers’ fields of view while they work may also become commonplace.

FAQ

Q: What do I need to prepare to visualize underground utilities with AR? A: Basically, you need digital data that includes the location information of the utilities and an AR-capable device to display it on site. For example, if you have drawing data for pipes and cables (CAD or GIS data), you can import it into an AR app on a tablet or smartphone and display it on site. For accurate overlay, it is ideal to prepare a receiver compatible with high-precision GNSS (RTK). Recently, small GNSS receivers that attach to smartphones (such as LRTK) have become available, making it possible to perform high-precision AR visualization easily without special surveying equipment.

Q: How accurate is AR display of underground utilities? A: When combined with high-precision GNSS positioning, AR can display underground utilities with errors on the order of several centimeters (a few in). Positioning aligned only with conventional GPS could result in errors of several meters (a few ft), but using RTK allows you to overlay models almost exactly where the drawings indicate. However, in places where positioning satellites cannot be received (such as inside tunnels or under elevated structures), errors may increase. In such cases, techniques like SLAM (self-position estimation using cameras or LiDAR) are used in combination to correct positions as accurately as possible. The accuracy required for construction management can be adequately secured.

Q: Can it be used on site without specialized knowledge or expensive equipment? A: Yes, with the latest solutions it is possible. For example, combinations of small devices and apps that attach to smartphones like LRTK allow intuitive operation by anyone. Previously, expensive equipment like total stations or specialized AR glasses and specialist skills were necessary, but now it is possible to perform AR visualization easily using everyday smartphones or tablets. Systems have become so simple that site workers can start using them after a short explanation. User interfaces are also designed to be intuitive for workers, and many solutions can be put to practical use on site after short training.

Q: What types of underground utilities can be visualized with AR? A: There are no strict limitations on types of utilities. Any buried lifelines—gas pipes, water pipes, sewer lines, power cables, communication cables, etc.—can be visualized, as long as their location information exists as digital data. For newly installed facilities, data can be obtained from construction drawings; for existing buried utilities without drawings, methods such as magnetic locators or exploratory excavation can determine positions, which can then be converted to data via point-cloud scanning with LRTK or similar. Once digitized, the information can be reused repeatedly in AR displays.

Q: Is this AR technology already widely used? A: In Japan, some major construction companies have begun pilot introductions of AR-based utility displays on sites and have reported results. High-precision outdoor AR systems have also attracted attention overseas. Recently, products like LRTK that anyone can use have been commercialized, and usage is expanding not only on sites with special conditions but also at general construction sites. With support from governments and industry groups, AR-based construction management is expected to spread further and become one of the standard tools on site. The Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction promotion is also providing administrative backing, and these AR applications are steadily becoming the new norm in construction.

Q: Is the cost-effectiveness of introducing AR technology justified? A: Initial investment is needed for equipment and data preparation, but the benefits are expected to outweigh those costs. Preventing damage to utilities reduces risks of large compensation payments and delays, and efficiency gains lead to labor cost savings and shorter schedules. There are reported cases where AR-guided piling and automated as-built inspections significantly shortened work time. The emergence of smartphone-based solutions has reduced the cost burden compared to dedicated equipment, and in the medium to long term the cost-effectiveness is promising. Moreover, AR helps prevent rework and complaints caused by misunderstandings among stakeholders, adding further value. Considering these effects, introducing AR is well worth examining.