How to Conduct On-Site Scanning Surveys of Buried Pipes｜Precisely Locate Underground Utilities with 3D Visualization

Underground buried pipeline facilities are diverse, including water pipes, sewer pipes, gas pipes, power cables, and communication cables. Accurately determining the locations of these buried pipes is an extremely important issue when carrying out civil engineering work and infrastructure maintenance. Misidentifying the location of buried pipes on site can lead to accidents or trouble during construction and poses a risk of occupational injury. Buried pipe scan surveys play an important role in addressing this. Here, we explain in detail methods for conducting these scan surveys efficiently on site. Accurately understanding the positions of buried pipes is a critically important task from both the safety and efficiency perspectives of construction. Buried pipe scan surveys are not merely preparatory work for construction; they are essential for the safe management of infrastructure and the fulfillment of social responsibility.

Basics and Importance of Buried Pipe Scanning Surveys

A buried pipeline scanning survey is a non-destructive method for detecting and recording the location, depth, and shape of pipeline facilities buried beneath the ground surface, and for visualizing that information. In the past the positions of pipes were sometimes determined by estimation, but by utilizing modern surveying technologies, more accurate and reliable surveys are now possible. Data obtained from scan surveys are processed as three-dimensional point cloud data, allowing precise positional information of the buried pipelines to be determined. This information is then referenced during subsequent design and construction phases and used in developing construction plans. The accuracy of buried pipeline scanning surveys is influenced by multiple factors, such as the performance of the equipment used, the geological conditions at the site, and the technical skill level of the survey staff.

Accurately understanding information about buried pipelines is not just for preventing accidents. It is also important from the perspective of improving construction efficiency. If the positions of buried pipelines are known precisely, construction plans can be developed in greater detail. Unnecessary detours in design and unexpected extensions of construction schedules can be avoided. In addition, scan surveys have value from the standpoint of maintenance management of buried pipelines. By periodically surveying the condition of existing buried pipelines, the progress of aging can be understood and replacement work can be carried out at an appropriate time. In this way, scan surveys are an important investigation method with multifaceted value. Improved accuracy in construction planning can shorten construction periods and reduce budgets, bringing significant economic benefits.

When conducting a scanning survey, advance preparation is extremely important. For the area to be surveyed, review records and drawings of existing buried pipes and establish an approximate idea in advance of where the buried pipes are located. In addition, you need to confirm beforehand whether on-site surveys can be carried out easily by checking the site’s topography and geology, traffic conditions, and surrounding environment. Carefully carrying out these preparatory tasks will greatly improve the efficiency of field surveys. It is desirable to conduct multiple site inspections and have survey staff fully understand the site conditions before starting the main survey. During the preparation stage, coordination with local governments and facility managers is also important. Collecting as much detailed information as possible about existing buried pipes will significantly enhance the efficiency and accuracy of the main survey.

The organizational setup for conducting surveys is also an important factor. Because buried pipe scanning surveys require advanced technical skills, it is desirable that appropriately trained specialist staff be involved. Assigning multiple survey staff to different roles and having them cross-check each other as the survey progresses helps prevent mistakes and misidentifications. It is also important to properly record survey progress and report to the client or other stakeholders as needed. Survey staff should possess not only sufficient knowledge of operating scanning equipment but also basic knowledge of civil engineering structures. By centering the team on staff with extensive field experience and having them mentor less experienced personnel during the survey, the overall technical level of the team will improve.

Details of scanning equipment and exploration technologies used on site

There are many types of equipment used for buried-pipe scanning surveys. The most commonly used is ground-penetrating radar (GPR: Ground Penetrating Radar). Ground-penetrating radar transmits electromagnetic waves from the ground surface and receives the waves reflected by subsurface objects to detect underground structures. This method can, under certain conditions, detect not only metallic pipes but also non-metallic pipes such as plastic pipes. Ground-penetrating radar is adopted at many sites because it offers high survey accuracy and a wide survey range. Antenna frequencies for ground-penetrating radar are typically selected in the range of approximately 500 MHz to 2000 MHz. Lower frequencies provide greater penetration depth, while higher frequencies provide higher resolution. Because the optimal frequency varies with soil conditions, selecting equipment appropriate to the site geology is important.

Electromagnetic survey equipment is also commonly used in buried-pipe scanning surveys. This equipment emits electromagnetic waves from a transmitter placed on the ground surface and detects changes in the electromagnetic field around buried pipes with a receiving sensor to determine the location of the buried pipes. It is particularly effective at detecting metal pipes and is characterized by a relatively fast survey speed. Electromagnetic survey equipment is relatively easy to operate and suitable for use in the field. This equipment generally uses electromagnetic waves in the frequency range of 50 Hz to several thousand Hz. When a metal pipe is present, a strong electromagnetic field is formed around it, so detecting that anomaly allows the position of the buried pipe to be identified. Because of its ease of operation, it is used as a primary screening survey at many construction sites.

In modern scanning surveys, it is common to use multiple exploration instruments in combination. The approach is to use ground-penetrating radar to grasp the overall subsurface structure and then use electromagnetic survey instruments to confirm the more detailed positions of buried pipes. By combining multiple instruments in this way, survey accuracy is further improved. Because each instrument excels with different types of buried pipes and geological conditions, it is important to select the optimal instrument according to site conditions. For example, ground-penetrating radar exhibits very high detection accuracy in sandy soils, while electromagnetic survey instruments can be more effective in clayey soils. Surveys using combined techniques compensate for the weaknesses of individual methods and yield more reliable results.

Surveys that utilize GNSS positioning technology are also indispensable in modern buried-pipe scanning investigations. GNSS positioning allows the location where a buried pipe is found to be recorded with high precision. In particular, by using an iPhone-mounted high-precision GNSS positioning device, real-time recording of location information at the site becomes possible. These location data are later used during three-dimensional visualization processing when setting the precise coordinates of buried pipes. High-precision GNSS technology makes it possible to record buried-pipe positions with centimeter-level accuracy (half-inch accuracy), greatly improving the reliability of data at the design stage. With such high-precision positional information, contact accidents with buried pipes during construction can be almost completely prevented.

Data processing techniques for survey data are also a critical factor that determines the success of scanning surveys. Data obtained from ground-penetrating radar and electromagnetic survey instruments are converted into an easily understandable format by dedicated processing software. In particular, by using point cloud processing software, it is possible to integrate data from multiple survey instruments and construct a three-dimensional model of buried pipes. This three-dimensional model allows the positions of buried pipes to be understood spatially, making on-site work more accurate. In the course of data processing, it is necessary to address many technical challenges, such as noise removal, integration of data from different instruments, and unification of coordinate systems. These data processing techniques are among the most important factors that influence survey accuracy.

Procedures for Conducting On-Site Surveys and Precautions for Ensuring Quality

When conducting buried pipe scanning surveys on site, it is important to follow a set procedure. First, carry out a site safety check before the survey. For surveys on roads with heavy traffic, measures such as implementing traffic control and installing safety barriers are required. Also confirm the site's safety environment, such as whether construction machinery is operating nearby or other works are in progress. Regarding safety equipment for survey staff, it is essential to prepare appropriate items according to site hazards, such as safety vests, helmets, and safety shoes. Ensuring safety at the survey site may require many preparatory tasks, such as advance notification to nearby residents and consultations with the police.

Next, prepare the survey equipment and perform the initial setup. For ground-penetrating radar and electromagnetic survey equipment, it is important to carefully carry out pre-survey checks such as confirming power supplies, cleaning sensors, and performing calibrations. Neglecting these preparatory tasks can reduce the accuracy of the survey data. Also, for GNSS positioning devices, check satellite reception and confirm in advance that appropriate accuracy can be obtained. Checking the remaining battery level of the equipment is also important. If the survey will last for a long time, it is advisable to prepare spare batteries. To deal with equipment troubles, it is recommended to carry simple repair tools and spare parts for parts replacement in the field.

Planning the survey route is also an important task. Based on existing drawings and interviews, infer the route along which the buried pipes to be surveyed are installed. Then use detection equipment to actually locate the buried pipes. When the survey route is long, it is efficient to establish multiple survey lines and carry out the investigation in stages. In locations with complex configurations, such as where buried pipes intersect, a more thorough survey is required. If there are large steps or obstacles on the survey route, address them in advance so that the survey equipment can be moved safely and stably. Setting the survey route requires a detailed examination not only of existing buried-pipe drawings but also of the local road structure and topography.

The method of recording data is also important for ensuring the reliability of the survey. For locations where buried pipes are detected, accurate coordinates are recorded using GNSS positioning. At the same time, survey staff directly observe on-site and enter attribute information — such as the type, size, and burial depth of the buried pipes — into the recording form. Having multiple staff members verify each other’s entries while recording helps prevent omissions and errors. Photographing the site where a buried pipe was detected to visually document the situation is also useful for later verification work. When recording data, consistency and accuracy of the records should be emphasized. The design of the recording form is also important, and it should be carefully considered in advance so that all necessary information can be recorded without omission.

Unexpected buried pipes may be detected during surveys. It is not uncommon to find buried pipes that were not included in the preliminary information. In such cases, it is important to record the location and attribute information for those pipes in the same manner. These data become valuable information for future construction planning and the maintenance management of buried pipes. Survey staff should remain calm when faced with unexpected discoveries and be diligent about properly recording the data. The discovery of unexpected buried pipes is an opportunity to enhance the reliability of the survey, and it is important to handle it carefully.

Three-Dimensional Visualization Processing of Survey Data and Its Applications

Converting data obtained from scan surveys into clear three-dimensional visualization models is extremely important for on-site operations. By using point cloud processing software, data from multiple survey instruments can be integrated and buried pipes can be represented within a single three-dimensional coordinate system. This three-dimensional model allows intuitive understanding of intersections between buried pipes and their relative positions to other underground structures. Three-dimensional models can be observed from various angles, enabling accurate understanding of the alignment and slope of buried pipes. Three-dimensional visualization makes design-stage considerations more concrete and more accurate.

When creating three-dimensional visualization models, data quality management is essential. For the data obtained from each survey instrument, it is necessary to perform certain processing such as detecting and removing outliers and organizing irregularly distributed data. Carefully carrying out these data-cleaning tasks improves the accuracy of the final visualization model. Also, when integrating data from multiple survey instruments, unifying the coordinate systems is critically important. Incorrect coordinate integration can cause the relative positions of buried pipes to be misrepresented, so this task requires particular care. Data quality management is the most important step in determining the reliability of the final visualization model.

After the visualization model is completed, it is important to apply that model on site. By importing the three-dimensional model into civil engineering design software, the position information of buried pipes can be incorporated into design work. In addition, by using devices equipped with AR display functions, it is possible to display the locations of buried pipes on site in real time. With such AR displays, construction staff can instantly grasp where on the ground surface the buried pipes are located. By utilizing AR displays, contact accidents with buried pipes during excavation work can be reliably avoided. The practical implementation of AR display technology has dramatically improved on-site safety.

Three-dimensional visualization models are also useful from the perspective of maintenance and management. For existing buried pipes, conducting surveys at multiple times and creating time-series visualization models enables understanding of the progression of deterioration of the buried pipes. Such long-term follow-up surveys make it possible to appropriately determine the timing for pipe renewal. Regular scan surveys allow early detection of anomalies such as settlement or movement of buried pipes, enabling prompt countermeasures. Time-series visualization models make the condition management of buried pipes more scientific and predictive.

To ensure the quality of visualization models, the reliability of data obtained from field surveys is crucial. If location information is not recorded with sufficient accuracy during the survey, the reliability of the final visualization model will be reduced. Therefore, it is important to adopt survey methods from the field survey stage that consider the assurance of data quality. Survey staff should verify each measurement until they are satisfied and re-measure any values that are in doubt. The reliability of visualization models is secured only through meticulous attention during the survey stage.

On-site Application Examples and Future Development Directions

The results of buried pipe scanning surveys are being utilized at various sites. In the planning stage of new infrastructure construction, accurate location information of existing buried pipes obtained from scanning surveys is indispensable to avoid conflicts with them. Based on this information, the construction route and construction methods are determined, greatly improving construction safety. In urban construction, multiple buried pipes are often densely clustered, and in many cases safe construction is difficult without scanning surveys. It also helps reduce construction costs by avoiding interference with buried pipes.

Moreover, the importance of scanning surveys has come to be recognized in the maintenance and management of existing buried pipelines. Regular scanning surveys make it possible to understand the deterioration status of buried pipelines and, by carrying out renewal work at the optimal time, minimize the societal impact of sudden buried pipeline failures. Utility companies are using the results of scanning surveys to formulate maintenance and management plans for the entire buried pipeline network. This enhances infrastructure resilience and ensures the stability of social life.

On-site scanning survey technology is expected to continue evolving. Advances in sensor technology will enable more accurate detection of buried underground pipes at greater depths. In addition, by leveraging technologies such as AI and deep learning, automatic analysis of survey data will become possible, and survey efficiency is expected to improve further. Automatic analysis will allow for consistent, high-quality survey results that do not depend on the skill level of survey staff.

The enhancement of tools to support field surveys is also anticipated as a future development. With the spread of high-precision GNSS positioning devices, real-time recording of location information at survey sites will become easier. The use of devices such as iPhone-mounted high-precision GNSS positioning units is expected to further improve the convenience of data acquisition in the field. By appropriately utilizing such tools, the practical value of buried pipe scan surveys will further increase. High-precision GNSS positioning devices enable survey staff to obtain highly accurate location information easily without specialized training, and are expected to lead to the democratization of survey operations. Going forward, buried pipe scan surveys will be easier for more people to carry out, and infrastructure safety management systems will be further strengthened.