5 Steps to Avoid Interference with Buried Pipes Using AR Before Excavation | On-site Workflow to Reduce Accident Risk

Beneath urban areas, various lifelines such as water pipes, sewer pipes, gas pipelines, power cables, and communication cables are laid out like a network. However, because these buried pipes are literally hidden under the ground and cannot be seen directly, they frequently present challenges in maintenance and construction sites. If, during excavation work, heavy machinery such as a backhoe (power shovel) accidentally damages a buried pipe, it can directly lead to serious incidents such as water leaks, gas leaks, or large-scale power outages. For example, damaging a water pipe can cause a major leakage incident, potentially resulting in water outages for surrounding areas and flooded roads. If a gas pipeline is damaged, it creates the risk of explosions or fires due to gas leaks, leading to serious consequences such as evacuation of nearby residents and prolonged suspension of gas supply. Damage to power lines can cause widespread power outages, and in the case of communication cables, it could sever emergency communication networks. If an accident damages buried pipes, restoration work and compensation measures require enormous time and cost, becoming a heavy burden for contractors. In fact, a survey by the Ministry of Land, Infrastructure, Transport and Tourism reports that more than 100 buried-pipe damage incidents occur each year, many of which are caused by accidental excavation due to insufficient pre-checks. Such incidents not only have a major impact on social infrastructure as a whole, but also lead to project delays and increased restoration costs. Thus, because a single buried-pipe accident can cause tremendous effects on surrounding areas and construction plans, it is critically important to take sufficient preventive measures in advance to reduce risk.

So how should we check underground pipes that are invisible to the eye? What has drawn attention in recent years is visualization of buried pipes using AR (augmented reality) technology. By overlaying location information of buried pipes onto the real-world scene captured by a smartphone or tablet camera, you can confirm the piping route and depth in real time, as if peering through the ground. Because it enables intuitive understanding without relying on drawings or guesswork, even young technicians without the experience of veteran workers can accurately grasp underground structures on the spot, contributing to safer operations. AR-based see-through displays of buried pipes are proving to be more than a mere convenience tool; they are having a significant effect as on-site safety measures.

This article explains five practical steps for using AR technology to avoid interference with buried pipes prior to excavation work. From the pre-excavation survey flow, to methods for interference checks using AR, on-site safety verification, and information sharing with stakeholders, we will walk through the entire process step by step. The applicable industries extend not only to construction and civil engineering but also to underground infrastructure in general, such as water and sewage, gas, electric power, and telecommunications. It is useful for practitioners involved in buried-pipe management, including construction consultants, surveying companies, municipal staff, and infrastructure management firms.

Step 1: Collect preliminary documents and verify information on buried pipes

First, identify from existing records as much as possible what kinds of buried utilities or objects exist beneath the planned excavation site. Make prior inquiries to the road administrator and each lifeline utility operator (water and sewer, gas, electricity, communications, etc.) and obtain location information for buried items. Then collect drawings, ledgers, and past construction records of buried pipes held by relevant agencies such as the water bureau and gas companies, and determine the pipe installation positions and burial depths. If records exist only on paper, carefully check them to avoid overlooking anything and, if necessary, digitize the drawings and organize them. Because old drawings may use different reference points or scales and therefore not match the site, compare multiple documents to assess their reliability.

Next, based on the collected drawings, we carry out on-site verification work. We infer the routes of underground conduits from the locations of related facilities exposed above ground, such as manholes, handholes, and fire hydrants, and mark them on the pavement with spray paint or similar. If there are locations where interference between the planned position and buried pipes is a concern, it is necessary to ascertain the details in advance. For important pipelines, without relying too heavily on old records, we consider confirming positions as needed using ground-penetrating radar (GPR) or utility locators, and even direct confirmation by small-scale trial excavation (test excavation). Especially in places where buried pipes are tangled, such as in urban areas, past repair works may have caused discrepancies between the information on drawings and the actual site conditions, so it is important to verify the reliability of the obtained information by comparing it with the on-site situation.

Traditionally, there have been cases where excavation proceeded by estimating the locations of underground pipes based on the experience and intuition of veteran workers. However, it is not easy to fully grasp complex, intersecting underground structures in one’s head, and any omissions in the records can lead to the unexpected appearance of pipes. Because even a slight oversight can cause a serious accident, it is essential to secure as reliable buried-pipe information as possible before starting excavation. The buried-pipe data collected and verified in this way forms the foundation for subsequent interference checks using AR.

Step 2: Preparing Data for AR Display and System Settings

Based on the collected information on buried pipes, prepare a dataset for AR display. Create 3D models and path data for each buried pipe from drawings and survey results, and import them into software or applications that support AR display. At this time, it is important to unify the coordinate systems of data obtained from different sources and to accurately transform and integrate them. When handling data acquired by multiple survey instruments, align them based on common surveying standards. If there are errors in coordinate integration, the positions of buried pipes displayed in AR on site may differ from their actual positions, potentially rendering safety measures ineffective. Therefore, rigorous quality control during the data processing stage is indispensable.

In recent years, systems have emerged that automatically generate 3D models of buried pipes from point cloud data acquired by LiDAR-equipped smartphones or terrestrial laser scanners and use them directly in AR. If the pipelines installed during construction are scanned and an accurate digital record is kept, that data can be used for AR display on site during later renovation work without having to pull out drawings.

Next, configure the display settings for buried pipe models on the AR system. By displaying models with different colors and shapes for each pipe type, you can visually distinguish buried pipes of different kinds, such as water pipes, sewer pipes, and gas pipes. For example, color-coding rules like blue for water pipes, brown for sewer pipes, and yellow for gas pipes are commonly used. Even in complex underground structures where multiple pipes are intertwined, such color-coded AR displays allow you to immediately identify the target pipe. Also, displaying attribute information such as burial depth as labels can help in judging excavatable depths. Rules for display colors and labels are increasingly being standardized internationally, making it possible to share information in a common format across different regions and sites. Prepare clear display settings in advance so they can be intuitively understood on site.

Also, before taking the data to the field, it is useful to test in advance whether the prepared data can be displayed correctly in AR. By roughly overlaying the model using a smartphone in the office, you can check for missing data or coordinate misalignments. If problems are found, make corrections at this stage to prevent issues on site during the actual operation.

Step 3: On-site Deployment of a High-Precision AR System

At last we launch the AR system on-site and perform a see-through display of buried pipes. First, attach a high-precision GNSS receiver to the smartphone or tablet brought to the site and configure it to receive correction information via RTK. If the terminal acting as the rover can obtain GNSS correction data from the base station, the device’s current position can be determined on the public coordinate system to within centimeters (in). Standard GPS positioning can produce errors of several meters (ft), but by using RTK-GNSS those errors can be reduced to a few centimeters (in), enabling precise alignment between digital data and the real-world environment.

Next, calibrate the device’s various sensors. Device orientation is detected by the electronic compass (geomagnetic sensor) and the gyroscope, but perform pre-calibration to prevent errors from the surrounding environment. Note that compass readings can be disturbed near metal objects or high-voltage power lines due to magnetic interference. Also, if the device is equipped with LiDAR, it scans surrounding terrain and structures in parallel with the camera feed, constructing a three-dimensional point cloud map in real time. This allows virtual buried-pipe models to be stably displayed along the ground’s undulations, and parts that become hidden beneath the surface are naturally occluded (遮蔽). By combining high-precision self-positioning via GNSS with attitude estimation and environment recognition from the IMU and LiDAR, discrepancies between the real world and the virtual model can be minimized.

When preparations are complete, launch the AR application and start displaying the buried-pipe data. Hold the camera over the site ground and confirm that the underground buried-pipe model is overlaid on the screen. Check whether the AR display matches known aboveground assets. For example, verify that the pipe model corresponding to a manhole visible on the surface is correctly displayed directly beneath it. If there is a slight offset in the display position, adjust the model position offset in the software and fine-tune it so that it matches the actual positional relationship. If you are using high-precision GNSS, large offsets should not occur, but it is reassuring to check this at the initial stage as a precaution.

Once you have confirmed that the displayed information is accurate, take the device and walk around the site a little to verify that the buried-pipe model stably follows your movement. Once the AR system has been set up on site in this way, proceed to the full interference check.

In the future, the practical implementation of AR displays using wearable devices such as smart glasses is also likely to advance. If workers wear head-mounted displays and can check AR information while using both hands freely, safety and work efficiency are expected to improve further.

Step 4: Interference Check and Safety Measures Using AR

Using an AR system, we verify on-site whether planned excavation locations will interfere with buried pipes. Just before starting excavation, we perform a final check by displaying a model of the underground buried pipes through the device’s camera to confirm that no pipelines run along the planned excavation route. If risky locations are found, we revise the construction plan or consider additional countermeasures before beginning actual excavation. After excavation begins, construction staff continue to proceed while continuously checking the subsurface conditions ahead on the AR display. Excavating while confirming the AR display in real time can almost certainly prevent contact accidents with buried pipes. In fact, survey results have reported that on sites using AR displays, the contact rate with buried pipes has fallen to almost zero compared with working from traditional paper drawings alone.

When excavation is actually underway and AR confirms that an embedded pipe exists in the direction the heavy equipment is moving, immediately suspend the backhoe's operation. Then change the excavation method for the relevant section. For example, switch to careful manual excavation for the area directly around the pipe, using shovels or spades to remove soil cautiously. If necessary, take measures to protect the exposed pipe from damage with shoring or cushioning materials. Also, it is safer to mark the location so the operator can visually confirm it—for example, by placing traffic cones directly above the pipe confirmed by AR or spray-painting warning lines on the ground. These safety measures can minimize the risk of pipe damage from unexpected excavation.

When carrying out tasks using AR, ensuring smooth communication within the on-site team is essential. Staff operating the AR display on tablets or smartphones, heavy equipment operators, and site supervisors must work closely together and continuously share information. Establish clear procedures for immediately relaying information confirmed in AR to operators, pausing work to confer when necessary, and the sequence of actions to follow. Regular meetings and training are required so that every team member understands how to interpret AR displays and the appropriate countermeasures. Also, if a buried object not shown in AR (such as an unknown cable) is exposed, stop excavation immediately, report it to the relevant parties, and consider response measures. Such calm, prompt handling can also prevent secondary accidents.

By combining AR interference checks with appropriate safety measures, the risk of accidents that damage buried pipes is greatly reduced. Workers' psychological anxiety is also alleviated, allowing them to focus on their work with a greater sense of safety. By maintaining vigilance toward buried pipes and proceeding with careful excavation, the overall efficiency of the construction work will consequently improve.

Step 5: Sharing information with stakeholders and updating records

Before beginning excavation work, share the information obtained from AR among the site stakeholders. Review the excavation procedures and safety measures together and confirm that there are no inconsistencies in the information. It is especially important that heavy equipment operators and site supervisors correctly understand the locations and depths of buried pipes shown in AR. When necessary, use screenshots or videos of the AR screen to explain while sharing visual information. By enabling everyone on site to form a concrete image of the underground conditions, safety measures can be thoroughly implemented under a common understanding.

Also, actively share the latest buried pipe information obtained on site with stakeholders both inside and outside the company. By using cloud services and GIS (geographic information system), you can instantly share data collected on site with stakeholders over the Internet. For example, a design engineer in the office can view in real time the 3D models and point cloud data uploaded to the cloud by field technicians, offer advice, or coordinate underground usage with other construction personnel. By digitally sharing data, geographically dispersed teams can collaborate smoothly and decision-making is accelerated.

Furthermore, the precise buried-pipe information obtained through this survey and verification will be recorded and retained as an asset for the future. The updated data on pipeline locations and depths will be reflected in infrastructure management ledgers and GIS databases to support future maintenance and the planning of other works. Information that tends to be dispersed on paper drawings can be preserved as digital data and used over the long term. Even when another excavation is carried out on the same road several years from now, safety confirmation can be achieved without repeating laborious trial excavations by displaying and using the 3D buried-pipe data accumulated this time on-site via AR. By thoroughly sharing information and updating records in this way, the organization’s overall safety management standards and operational efficiency will be improved.

By leveraging these AR technologies, the management of underground buried pipes, which previously relied on the experience and intuition of veteran workers, becomes data-driven, creating an environment in which anyone can make accurate judgments and carry out work on site. As a result, construction errors and rework are reduced, and it is expected to lead to a reduction in lifecycle costs in the future.

Cases of implementing AR display technology for buried pipe detection are increasing around the world, and at construction sites in urban areas where multiple buried pipes are densely clustered, safety checks using AR are becoming indispensable. Especially in the public works sector, where safety standards are being tightened, the use of AR display technology is increasingly becoming a condition for winning contracts. In Japan as well, major construction companies and public works sites are adopting AR systems, and demonstrations have confirmed improvements in safety and efficiency. Going forward, further technological advances are expected to enable the development of systems that work with AI (artificial intelligence) to automatically detect hazards and alert workers. Aiming for zero buried-pipe accidents, AR technology will be an important key to shaping the future of safety management on construction sites.

Finally, I will touch on the technical elements that support these buried-pipe AR interference-avoidance efforts. The positioning accuracy of AR systems used on site is extremely important, and without high-precision positioning the reliability of AR displays cannot be ensured. Since the GPS built into ordinary smartphones has errors of several meters (several ft), achieving the centimeter-level (half-inch accuracy) precise alignment described in Steps 3 and 4 requires the use of an external high-precision GNSS receiver. In recent years, devices that can be attached to a smartphone to perform RTK-GNSS positioning easily have appeared. The environment in which a single smartphone can perform precise positioning and AR see-through visualization is coming together, and the era in which each technician can carry high-precision tools and use them in field work is imminent. For example, using LRTK (an iPhone-mounted GNSS high-precision positioning device) makes it possible to obtain centimeter-level positioning (half-inch accuracy) on site immediately and to accurately align the displayed positions of buried-pipe models with the actual coordinate system. By combining high-precision positioning tools, the effects of all five steps can be maximized, greatly contributing to reducing the risk of buried-pipe damage accidents. Introduce new safety management methods that leverage AR and positioning technologies to further improve the safety and productivity of underground infrastructure construction.