ICT活用で精度アップ！土木出来形管理効率化のポイントとは？

As-built management (dekigata management) at construction sites is a critical construction-control process that verifies and records whether completed structures conform to the design in shape and dimensions. Especially for public works, measured data must demonstrate conformity of the actual as-built condition to the contract-specified standards, which is a prerequisite for passing inspections. However, the current situation relies heavily on manual as-built management; measurement and photographic documentation are very time-consuming and carry risks of missed measurements or missing records due to human error.

The key to solving these issues and dramatically improving the accuracy and efficiency of civil engineering as-built management is the use of ICT (information and communication technology). This article reviews the current state and challenges of as-built management and introduces specific ICT technologies such as drone surveying, GNSS surveying, point cloud data processing, and cloud-based as-built management. From a field perspective, it explains the benefits these technologies can deliver—accuracy improvement, labor savings, assurance of objectivity, enhanced safety, and digital archiving—and organizes the main points so they are easy for beginners to understand. At the end of the article, we also touch on the latest surveying method combining smartphones and compact GNSS (LRTK) and offer tips for on-site implementation.

土木出来形管理の現状と課題

As-built management is the construction-control process of checking and recording whether completed structures and ground conditions match the shapes and dimensions shown in the design drawings. Traditionally, as-built management has been conducted mainly by manual measurements using tools such as tape measures, leveling staffs, and spirit levels. It is common practice to measure heights, widths, and thicknesses at each construction location by hand, compile the differences from the design values into drawings or as-built management tables, and check them.

However, manual as-built management has various pointed-out problems. Specifically, the following issues exist:

• Requires manpower and time: Field surveying and recording require multiple people, including experienced personnel, and the workload increases dramatically for large structures. If measurements are done carefully, inspection preparation can occupy the team until the last minute of the construction schedule.

• Limited measurable points and risk of oversight: Manual work only yields fragmentary dimensions at specific points, and the number of points that can be obtained at one time is limited. Therefore, it is difficult to grasp the overall shape in a surface-wise manner, and differences from the design in unmeasured areas can easily go unnoticed.

• Complicated photo record management: As-built management requires photographing parts that will be hidden later, such as buried items or rebar, and keeping those photos as records. Traditionally, photos were pasted into paper ledgers or organized into folders, a tedious process that in busy worksites often leads to forgetting to take critical photos.

• Cumbersome reconciliation with design values: To determine whether measured values fall within specifications, they must be compared against the design drawing tolerances. On sites with many measurement points, writing measurement results onto drawings or entering them into spreadsheets is a heavy burden, and including report preparation, the inspection process is extremely inefficient for inspectors as well.

Thus, traditional as-built management has drawbacks—“can only measure one place at a time,” “subject to human error,” and “data organization is time-consuming”—creating significant burdens and risks for field engineers.

ドローン測量で広範囲を効率計測

One ICT technology that can be applied to as-built management is drone surveying. By aerially photographing the site with a camera mounted on a drone and generating 3D survey data (point clouds) from many photos, large construction areas can be measured in a short time. The time required for this work is orders of magnitude less than traditional manual surveying; surveys that used to take several days can sometimes be completed in a few hours with a drone. Because it is a non-contact measurement from the air, it is also a major advantage that the as-built condition can be safely captured on steep slopes or cliffs where people cannot enter. In recent years, drones equipped with RTK-GNSS have appeared, allowing high-precision positioning information to be recorded with photos during flight, so the generated point clouds can achieve accuracy within a few centimeters (within a few inches).

The 3D models created from drone-acquired photos reproduce fine surface irregularities of the ground in detail. Therefore, by comparing with design data, you can verify whether finished heights and gradients fall within specified ranges across the entire surface. Evaluation of as-built conditions, which was traditionally judged by a limited number of measurement points, can now be performed in a surface-wise and three-dimensional manner using drone point clouds, preventing oversights and improving quality. The obtained 3D data can also be used for construction progress management and post-completion records, and because all stakeholders can share the same information, it becomes objective inspection material.

GNSS測量で即時・高精度な位置出し

Another important technology for as-built management is GNSS surveying (satellite positioning). Using a GNSS receiver, coordinates of measurement points can be obtained in real time on site and compared with the design reference. Particularly, RTK (Real Time Kinematic) GNSS surveying uses correction information from a base station to instantly cancel out errors and achieve positioning accuracy on the order of centimeters. In the past, expensive GPS surveying instruments and skilled technicians were required, but nowadays network-type RTK services and user-friendly GNSS terminals make high-precision positioning relatively easy even on site.

The advantages of GNSS surveying are its responsiveness and labor savings. Unlike conventional total station surveys, which require line-of-sight setups, GNSS simply provides coordinates at the location where the receiver is placed, so you can move to the point you want to measure and get coordinates on the spot. For example, to check as-built conditions over a large development area, one person can carry the antenna and巡回measure measurement points, eliminating the need to form a survey team or repeatedly set up equipment between points. Because positions can be directly tied to a reference coordinate system, acquired data are easy to integrate with design CAD drawings and other measurement results. Moreover, because surveyors do not have to enter hazardous locations, GNSS contributes to improved safety. Even at sites where heavy machinery is operating or on busy roads, positions can be identified from a distance with GNSS, reducing workers’ risk exposure. Except for spaces where GNSS cannot be used alone—such as inside tunnels—GNSS has become an indispensable positioning method for as-built management.

点群データ処理で精密な現場解析

Properly processing and analyzing the vast point cloud data acquired by drones or 3D laser scanners can dramatically improve the accuracy and efficiency of as-built management. Point cloud data record many points that compose the site, each with XYZ coordinates—a “3D copy of the site” that captures the space almost continuously. Points are arranged at high density, on the order of several centimeters or less (several inches or less), so they can capture subtle irregularities down to millimeter-level detail (fractions of an inch).

By processing the acquired point clouds with specialized software, comprehensive comparisons with design models or reference surfaces become possible. For example, overlaying as-built point clouds with design data and calculating differences allows immediate judgment of constructed volumes and finish accuracy. Visualizations such as colored heat maps showing deviations from the design, and automatic extraction of areas that exceed tolerances, are easy to perform. The Ministry of Land, Infrastructure, Transport and Tourism has also introduced a new “surface management” method that evaluates earthwork quantities and pavement thickness using 3D measurement data, and the use of point clouds is becoming the new standard in as-built management. Inspection work that was formerly done with experienced technicians poring over drawings and measurement values can now be done accurately and efficiently by anyone using point cloud processing.

Furthermore, various secondary uses are possible from point cloud data, such as calculating volumes and cross-sectional shapes. You can instantly compute fill and excavation quantities from differences between the current and design surfaces, or automatically generate longitudinal and cross-sectional drawings at arbitrary locations. If as-built point clouds themselves are preserved as final construction documents (3D as-built data), they are useful for monitoring deformations that appear after construction. Having a digital, site-wide record significantly raises the level of construction management and quality assurance.

クラウド型出来形管理でデータ共有と客観性

Cloud-based as-built management systems further promote ICT utilization. This refers to a system in which survey data, photos, and records acquired on site are uploaded via the Internet to cloud servers and shared or viewed by all stakeholders. Consolidating data in the cloud enables real-time information exchange between the field and the office, greatly improving the efficiency and transparency of construction management.

Using the cloud markedly advances the objectivity of as-built management and the creation of digital archives. As-built information that was previously managed on paper documents or local PCs can be uploaded to the cloud so that anyone can view the same data. There is no worry about unauthorized alteration or loss, and during inspections the client or inspectors can view and confirm data remotely from the office—enabling “remote attendance” at inspections. There are also systems that automatically generate as-built management diagrams and report forms in the cloud, so entering numbers on site can directly produce as-built management drawings and reports, contributing to operational efficiency.

Moreover, accumulated as-built data in the cloud proves valuable as a digital archive. If 3D data and photos at completion are retained, the exact past condition can be understood years later when carrying out repairs, aiding in planning. Because cloud data do not deteriorate or get lost like paper records, the cloud is effective for passing information along over the infrastructure life cycle. Thus, adopting a cloud-based system not only reduces the workload of as-built management but also increases asset value through long-term data utilization.

ICT出来形管理がもたらす5つのメリット

Introducing ICT-based as-built management yields the following advantages:

• Improved accuracy: Non-contact 3D measurement can comprehensively digitize the site, enabling detection of minute deviations and dramatically improving as-built management accuracy. Areas previously overlooked by manual surveys can be covered, and accurately understanding differences from design leads to early detection and correction of quality defects.

• Labor savings: Measurements by drone or GNSS drastically shorten work time; processes that used to take several days can be completed in a few hours. Losses due to waiting for heavy machinery or re-measurement are reduced, allowing efficient as-built management with fewer people. Even novices can quickly obtain results through automated software calculations without relying on the skills of veteran personnel.

• Objectivity: Digital-data-based as-built management provides objective evidence rather than relying on subjective judgment or intuition. Measurement results are stored as numbers and 3D models, and all stakeholders can share the same information, allowing issues to be verified and discussed based on data. Transparent records increase trust from clients.

• Safety: Non-contact measurement technologies reduce the need for workers to enter hazardous areas. Drones can measure from above and GNSS from a safe distance, reducing fall and contact risks near slopes or heavy machinery. Reducing the number of required personnel also lowers accident and heatstroke risks during movement.

• Digital archiving: All as-built information is saved as data, becoming a valuable recorded asset for the future. If drawings, measurements, photos, and point cloud data remain in the cloud, they can be retrieved and used after project completion. Digitally archived as-built data make it easy to reference past information during maintenance or future projects, supporting better decision-making.

スマホ×小型GNSSで始める手軽なICT測量（LRTK）

Recent surveying technology that combines smartphones with compact GNSS significantly lowers the barrier to introducing ICT as-built management. For example, the smartphone surveying solution called LRTK enables anyone to perform centimeter-level surveying simply by attaching a palm-sized high-precision GNSS receiver to a smartphone. By combining the smartphone’s built-in camera or LiDAR sensor to perform 3D scanning, point cloud data of the site can be obtained instantly, and on-the-spot comparisons with design drawings and as-built pass/fail determinations can be made.

The advantage of such smartphone surveying devices is that they are affordable and easy to use. With a compact GNSS unit weighing a few hundred grams (a few ounces) and a commercially available smartphone, there is no need to prepare special equipment—just launch a dedicated app and point the camera to complete the survey. Because they are intuitive to operate even for those who are not experienced surveyors, each field staff member can potentially use their own smartphone as a surveying instrument. Initial costs are far lower than those of conventional surveying equipment, making one-device-per-person deployment realistic and attractive for small and medium-sized contractors.

Additionally, data acquired with a smartphone can be automatically uploaded to the cloud and shared, enabling office staff to check results the moment measurements are taken on site. Combining photo measurement or AR (augmented reality) features expands applications to include photographic records of as-built conditions and visualization of buried items on drawings. This technology is truly a first step in on-site digital transformation (DX), and even sites that could not afford expensive ICT construction machinery or large equipment can start digitalization through smartphone surveying and expect significant benefits. Try these easy-to-use solutions and experience the efficiency gains in as-built management on your site.