Improving Safety in Slope Surveying: Reducing Hazardous Work with Labor-Saving 3D Point Cloud Technology

Introduction: Why is slope surveying hazardous?

A slope (norimen) refers to an inclined surface formed artificially or naturally on roads, dams, or development sites. Accurately surveying the shape of such slopes is indispensable for construction planning and as-built control. However, the actual sites of slope surveying often feature steep inclines and unstable ground, making the surveying work itself highly hazardous. In practice, occupational accidents have occurred, such as slips and falls while surveying on poor footing or being struck by falling rocks from above. High-altitude and slope work on slopes always carry the risk of falls or collapses, making surveying a nerve-wracking task for surveyors.

The dangers of slope surveying accompany every phase of construction. Pre-construction site investigations require stepping onto steep slopes to understand topography and geology, and during construction and post-completion inspections there are occasions when measurements on the slope are required. In other words, it becomes necessary to approach the slope repeatedly throughout pre-construction, construction, and post-construction phases. How to carry out these tasks safely has been a long-standing challenge.

Problems with conventional methods: slope intrusion, high-altitude work, and personnel burden

In conventional slope surveying, it was common for surveying staff to enter the slope directly to take measurements. For example, to measure points on a slope with a total station, a worker carrying a prism must climb the steep slope to the installation points. Height measurements using tape measures or ranging rods require people to move along the slope while measuring. Such methods—where people enter the slope and measure directly—are always accompanied by the risk of slipping or falling.

To perform high-altitude work safely, traditional measures include installing lifelines and wearing safety harnesses. However, no matter how careful one is, risk can never be reduced to zero, and fundamentally reducing the amount of high-altitude work on slopes has been seen as the real solution. In addition, slope surveying imposes heavy physical burdens, requiring multiple personnel to be deployed and rotated. Achieving the required accuracy often depends on veteran surveyors, the work is time-consuming, and it becomes a significant burden amid labor shortages.

Furthermore, conventional methods can only measure a limited number of points, so the resulting data are fragmentary. To understand the overall shape of a slope requires measuring many points, but due to danger and effort, compromises are sometimes made with a minimum number of sample points. This can lead to oversights and measurement errors, leaving issues in terms of quality control.

Emergence of "non-contact × labor-saving" surveying with 3D point clouds

Recently, advances in ICT have produced new surveying methods that realize non-contact, labor-saving workflows. At the core of this is measurement using 3D point cloud technology. A point cloud is a collection of numerous 3D coordinate points obtained by laser scanners or photogrammetry, digitally reproducing the shape of an object with high accuracy. By converting a slope into a point cloud, the entire slope can be reconstructed on a computer, and required dimensions and gradients can be measured later at will.

The biggest feature of 3D point cloud surveying is that data can be collected remotely without the surveyor directly contacting the slope. Because distance and shape are measured using laser beams or photography, people do not need to enter hazardous areas. Also, tasks that previously required several people shift to being primarily equipment-operated, enabling measurements by a small number of personnel. It is attracting attention as a groundbreaking solution that truly realizes "non-contact × labor-saving."

With the push for i-Construction and ICT-enabled construction by the Ministry of Land, Infrastructure, Transport and Tourism, adoption of 3D point cloud technology at worksites is progressing. In slope works, cases of using three-dimensional measurement for initial surveys and as-built control are increasing. By replacing dangerous work that previously required climbing slopes with digital technology, dramatic improvements in safety and work efficiency can be achieved.

Methods overview: using TLS, drones, and smartphone RTK scanning appropriately

Although we generally refer to 3D point cloud surveying, there are several methods available on site. Here we introduce the characteristics and appropriate uses of three representative methods: terrestrial laser scanners (TLS), drone aerial photogrammetry, and the recently spreading smartphone RTK scan.

Terrestrial Laser Scanner (TLS)

A TLS (Terrestrial Laser Scanner) is a tripod-mounted laser measurement device that emits laser light from the ground directly at the object to acquire high-density point cloud data. TLS’s strengths are the ability to measure distance with millimeter-level (0.04 in) high precision and its long reach, able to measure tens to hundreds of meters (tens to hundreds of ft) ahead. By placing equipment in safe positions such as the bottom of the slope and scanning the entire slope, detailed terrain data can be obtained without people climbing the slope.

Even on slopes with many trees or rocks, TLS can construct a model including hidden parts by scanning from several vantage points with good lines of sight and merging multiple point clouds. In practice, when comprehensive measurements are required on steep terrain, TLS is sometimes used to complement drone measurements in areas blocked by vegetation. The equipment is large and requires specialized knowledge, but it offers high precision and reliability and is useful for as-built confirmation of slope geometry.

Drone photogrammetry (UAV aerial survey)

Drone photogrammetry uses aerial photography to create point clouds of a site. A camera-equipped UAV (unmanned aerial vehicle) photographs terrain including slopes, and 3D models are generated from multiple photos using photogrammetry techniques. The biggest advantage of drone surveying is that it can cover large areas in a short time. Large-scale slope surveys that would take people days to complete can be captured as point cloud data in a short flight.

Drone photogrammetry enables complete non-contact surveying since the surveyor does not need to enter the slope and can shoot from above. Because it can photograph from directly overhead or oblique angles, it records complex terrain without omission, including areas that are difficult to see from the ground. However, slopes densely covered with trees make it difficult to extract the ground surface from photos, so combining with ground-based measurement such as TLS is effective. Drone flights also require consideration of conditions such as battery life and wind, but when conditions are met, drones are an extremely efficient and safe surveying method.

Smartphone RTK scan (smartphone surveying)

The recently introduced smartphone RTK scan combines smartphones with high-precision GNSS (RTK) receivers to obtain point clouds. The latest iPhones and iPads are equipped with LiDAR sensors, and by combining these with RTK centimeter-level positioning (cm level accuracy (half-inch accuracy)), anyone can easily perform 3D surveying. With dedicated smartphone apps, simply walking around the site while scanning allows you to generate point clouds in real time around the walking path.

The advantage of a smartphone + RTK is mobility and ease of use. Because the device fits in your pocket, heavy equipment or special piloting skills are unnecessary, allowing immediate surveying whenever needed. It can be used as a one-person, one-device surveying tool and is especially powerful for small slopes or supplementary detailed measurements. Since point clouds obtained with RTK always carry highly accurate position coordinates, aligning positions in post-processing is smooth. When drone flights are difficult or TLS is unnecessary for a simple survey, smartphone scanning becomes a new option.

On-site safety benefits: zero contact, fewer personnel, and no scaffolding

The safety benefits that 3D point cloud technology brings to sites are immeasurable. Here we summarize the particularly important points of "zero contact," "reduced personnel," and "no scaffolding."

• Zero contact: The greatest benefit is that surveying staff do not have to enter hazardous areas. Laser scanning and drone aerial photography allow data acquisition without touching the slope, greatly reducing the risk of slips and collapses. Even slopes that cannot be approached due to collapse risk can be safely assessed with remote measurement. By making surveying non-contact, the risk of occupational accidents on site drops dramatically.

• Reduced personnel: Slope surveys that previously required multiple people can be conducted with a minimal number of staff by using point cloud technology. For example, drone surveys can cover large areas with about one operator and one observer, and TLS can be operated and data-collected by one to two people. Reducing personnel reduces the number of people exposed to danger. Also, because surveys can be completed quickly with fewer people, prolonged high-altitude work is avoided, reducing physical and mental burdens on workers.

• No scaffolding: Introducing point cloud surveying can eliminate the need to erect scaffolding or use aerial work platforms solely for surveying. Traditionally, temporary scaffolding or lifting workers with aerial work platforms was used to safely access slopes; those scaffolding erection tasks themselves carry accident risks. Switching to non-contact surveying removes the need to install scaffolds or suspension equipment in the first place, simplifying site preparation and reducing surrounding safety measures, which improves overall safety levels.

In this way, 3D point cloud technology fundamentally removes situations in which people are exposed to danger, ensuring safe surveying operations. It reduces risks not only for the surveyors themselves but also for nearby workers and third parties, contributing to overall site safety management.

Automating reports with point clouds: reducing the burden on construction managers

Once 3D point clouds are acquired, subsequent data processing and report creation are also dramatically improved in efficiency. Conventionally, confirming as-built conditions of a slope required plotting field-measured points on drawings, calculating deviations from design values, and compiling reports. Using point cloud data, much of this work can be automated by software.

For example, to check the finished slope gradient, a cross section line can be extracted from the point cloud and compared with the design cross section to analyze differences. Surface-based as-built evaluation, which would be difficult with dozens of hand-measured points, becomes possible with a single scan. As-built management software can compare point clouds with a 3D design model to color-code areas of insufficient thickness or automatically calculate volumes of embankment and excavation. Construction managers can confirm quality based on objective evidence shown by point clouds and take early corrective action when issues are found.

Point cloud technology also helps significantly with report preparation. By sharing point cloud data in the cloud, detailed analysis and drawing creation can be done on office PCs. Extracting required numerical values from the vast point cloud collected on site and automatically reflecting them in reports prevents manual calculation and data-entry errors. Photo management and recording in survey field notebooks are also digitized, reducing the burden of paper-based organization.

Recently, efforts to visualize point cloud data combined with AR (augmented reality) have attracted attention. Viewing the site through a tablet can overlay a predicted completion model based on the acquired point cloud onto the real scene, enabling intuitive recognition of deviations between design and actual conditions. This makes it possible not only to "check as-built numerically" but also to "visually confirm as-built," facilitating explanations to clients and stakeholders.

Automation and visualization through 3D point cloud use greatly reduce the burden on construction managers and improve as-built management accuracy. Freed from tedious data processing and report creation, engineers can spend more time on creative tasks and overall management.

Compatibility with client inspections: smoother inspections with 3D data

Point cloud data acquired for as-built management also benefits client-side inspection work. Traditionally, for final inspections the client would conduct on-site verification based on drawings and measured values submitted by the contractor, and re-measurements would be performed as necessary. With objective digital records in the form of 3D point clouds, inspectors can evaluate as-built conditions while directly viewing the data, making inspections smoother than before.

For example, if point cloud data for a slope project are submitted at final inspection, the client can freely view the slope geometry on an office PC and check necessary sections and gradients. Areas that are hard to see on site can be easily checked in virtual space, reducing the risk of overlooking critical points. Also, if comparison results between the point cloud and the design model (such as color-coded heat maps) are provided, the acceptability of as-built conditions can be judged at a glance, smoothing the communication until inspection approval.

The Ministry of Land, Infrastructure, Transport and Tourism’s “As-Built Management Guidelines (draft) — Slope Works” also indicates as-built management methods using three-dimensional measurement technologies and recommends using point cloud data as part of the completion documents. This means that the foundation for clients to accept 3D data as official deliverables is being established. In practice, some sites that adopted point cloud as-built management use electronic deliverables directly for inspection instead of paper drawings.

By sharing 3D data between contractor and client, inspections based on data with high transparency become possible. For clients, the need to enter hazardous slopes to check details is reduced, enabling efficient and safe quality verification. Ultimately, data-mediated trust is built, leading to faster inspections and smoother consensus building.

Conclusion: Protecting survey safety and quality through labor reduction

Using 3D point cloud technology in slope surveying is revolutionizing work that was once fraught with danger. Through non-contact measurement and labor reduction, surveyor safety can be secured while detailed data acquisition improves survey quality—resolving challenges that were once difficult to reconcile. By supplementing and substituting labor with technology, we can protect workers’ lives and health while raising the level of construction management and quality assurance.

Improving safety and efficiency go hand in hand. Reducing hazardous work decreases occupational accidents and prevents project interruptions and personnel loss. High-precision as-built management using point clouds reduces the risk of rework and additional corrections. In other words, the leeway created by labor and effort reduction generates a virtuous cycle that boosts overall site productivity and quality.

As the construction industry faces chronic labor shortages and an aging skilled workforce, DX tools like 3D point cloud technology will become increasingly important. To achieve safe, worker-friendly sites while ensuring reliable quality, please consider adopting these new technologies.

Bonus: Start safe point cloud surveying with smartphones × LRTK

For those who feel that acquiring the latest equipment is a high hurdle, there is good news. Recently, solutions have emerged that allow easy point cloud surveying using smartphones. A representative example is surveying with a smartphone + LRTK. LRTK is a technology that turns a smartphone into a centimeter-accuracy surveying device (cm level accuracy (half-inch accuracy)) by attaching a compact RTK-GNSS receiver to the phone.

Using a smartphone and LRTK, 3D measurement of slopes that previously required expensive specialized equipment can be conducted easily by one person. For example, even points at the top of a steep slope that cannot be approached can be acquired from a safe location by capturing the target with the smartphone camera and obtaining its coordinates. Scanning the site while walking with the smartphone’s built-in LiDAR scanner can acquire a slope point cloud in minutes. Because RTK provides absolute coordinates to the acquired point cloud, no correction work is needed later when comparing with design drawings or calculating as-built quantities.

Smartphone surveying using LRTK is attractive because it achieves labor reduction, improved safety, and report efficiency with a small device. Acquired point cloud data can be uploaded to the cloud and shared immediately, allowing volume calculations and drawing creation in the office or 3D viewing with stakeholders. AR features can overlay design models on the as-built point cloud to help confirm as-built conditions and reach consensus at the construction site. Surveying tasks that previously relied on specialists are becoming doable by anyone with a smartphone.

As a first step toward safe and efficient slope surveying, consider point cloud surveying with smartphone × LRTK. By skillfully adopting the latest technologies, you can protect site safety and quality while improving productivity.