Slope 3D Survey DX Case Study: Productivity and Safety Improved with LRTK Introduction

Introduction: What are the challenges in slope surveying?

"Slope" refers to the inclined parts of roads and reclaimed land, where works such as shotcrete or slope-frame construction are carried out to prevent collapse. In these slope works, it is essential to accurately survey the post-construction slope geometry (as-built) to confirm it matches the design. However, surveying on steep slopes has posed major challenges in terms of safety, workload, and time. With the Ministry of Land, Infrastructure, Transport and Tourism promoting *i-Construction*, site digitalization (DX) has attracted attention, and new solutions are being sought to overcome the limits of conventional slope surveying methods. There have been reports of falls and near-miss incidents during slope surveys, so improvements are desired not only to boost productivity but also to ensure worker safety. This article organizes the problems of traditional as-built slope surveys and, through a case study of on-site introduction of the smartphone 3D surveying system "LRTK", concretely presents points that led to improvements in productivity and safety.

Limits of traditional methods: Danger, labor, and reporting burden

Traditional as-built slope surveys have the following issues:

• Danger: Survey personnel had to step onto steep slopes to measure with tape measures or staffs, or climb scaffolding installed on the slope for measurements. There was always the risk of falls or falling rocks, imposing a heavy burden on safety management. Although aerial lifts have sometimes been used, in narrow mountain areas vehicles cannot always be brought close enough to be used.

• Labor hours: On steep terrain, simply obtaining each survey point took considerable time. Teamwork with multiple people and placement of safety watchers for high-altitude work were also required, consuming much manpower and man-hours. On large slopes, measurements could take from half a day to several days.

• Reporting burden: Based on heights and gradients measured on-site, drawings and as-built management tables had to be created manually. Organizing numerous survey points, calculating errors versus design values, and compiling them into prescribed formats was tedious. If any points were missed, revisiting the site was necessary, which placed a heavy burden on site supervisors and surveying technicians.

Background of the LRTK introduction site: Trigger and reasons for selection

At a slope construction site facing the above issues, ensuring safety and improving efficiency of as-built surveys became urgent. In fact, there had been a near-miss where a worker slipped during a conventional survey, prompting the site supervisor to seek a non-contact way to measure safely. With limited personnel and the need to meet the construction schedule, labor-saving and faster surveying were also required.

At that time, the site supervisor learned about a new smartphone-based 3D surveying system called "LRTK" at a construction ICT seminar. LRTK is a system in which a small RTK-GNSS receiver is attached to a commercial smartphone, and by scanning the surroundings with the phone’s camera or LiDAR, high-accuracy 3D point cloud data can be obtained. Unlike drone photogrammetry, it does not require flight permissions or large-scale equipment, and its ability to be operated by one person in a short time was highly valued, so it was introduced on a trial basis. Of course, the client was briefed in advance about the new method, and the trial was conducted after obtaining consent regarding conformity with as-built management procedures and the format of deliverables.

The deciding factors were that it was low-cost and easy to operate. The fact that anyone on-site could handle it without purchasing expensive laser scanners or arranging specialist operators was appreciated. As described later, LRTK also integrates with cloud services, enabling sharing of point cloud data and automated creation of as-built reports, so it was expected to streamline preparation of submission materials to the client.

Introduction process: From preparation to on-site operation

Let’s briefly follow the process from preparing to implementing LRTK for surveying.

• Preliminary preparation: First, the contractor procured the LRTK Phone (a smartphone-mounted RTK-GNSS receiver) and installed the dedicated app on a compatible smartphone. In the initial setup, settings were configured to receive correction information (QZSS CLAS signals and reference station data via the network). To align the positioning datum with the site coordinate system, verification measurements at known points were also performed.

• On-site surveying: On the survey day, the worker attached the LRTK device to the smartphone with a magnet and brought it to the site. After arriving, they launched the app, received RTK correction signals from satellites, and began positioning immediately. From safe positions such as the base or side of the slope, they held up the smartphone and walked to scan, sweeping their view across the entire slope. Even complex terrain was captured down to the last detail as 3D point clouds in just a few minutes.

• Data processing: The acquired point cloud data was automatically uploaded from the smartphone to the cloud on-site. A high-precision point cloud model was generated on the LRTK cloud service, and the data could be checked immediately from an office PC. Operation of conventional point cloud processing software was unnecessary, so once scanning on-site was complete, the as-built 3D model was almost finished.

• Report creation and utilization: From the point cloud on the cloud, required cross-sections and dimensions can be obtained immediately. For example, overlaying the design cross-section with the measured point cloud to check slope thickness and gradient can be done with a click. Since measured values required for as-built management documents are automatically calculated, the person in charge only needs to check and export them to complete the as-built report creation. The point cloud data itself can also be shared with the client, enabling intuitive 3D presentation of finish conditions that are hard to convey with paper drawings alone.

Results obtained: Reduction in survey days, personnel, and reporting time

Using LRTK achieved greater efficiency than expected. Here are some specific results:

• Shorter survey duration: Sites that previously took 1–2 person-days for as-built slope surveys were completed within half a day after LRTK introduction. For example, a slope 50 m long with a 30 m elevation difference could be measured on-site in about an hour in the morning, and the as-built data整理 could be finished the same day (a 75% reduction in work time).

• Reduced required personnel: Previously, surveys were conducted with a surveyor plus 2–3 assistants (3–4 people total), but with LRTK’s non-contact measurement, the work can be completed by one person in principle (at most two people if a safety watcher is required). With personnel significantly reduced, staff could be reallocated to other construction tasks, improving overall site productivity.

• Reduced report creation time: By using as-built dimensions automatically calculated from point clouds, report preparation time was dramatically decreased. Tasks that formerly took half a day (4 hours) or more—organizing survey points, drafting drawings, and transferring data into tables—now require only about 30 minutes of data checking and export after LRTK introduction. This reduced administrative burden on survey staff and allowed more time for quality control tasks.

Tangible safety improvements: Non-contact surveying of hazardous areas and reduced personnel

Site staff strongly felt the safety benefits of this introduction. The greatest effect was that no one needed to enter dangerous steep slopes. Previously there were occasions where workers had to climb the slope with lifelines, but with LRTK, surveying can be done from a safe distance. For example, even on fragile cliffs or areas at risk of collapse, current conditions can be captured non-contact, reducing the risk of secondary accidents.

Additionally, reducing personnel lowered the exposure of staff to on-site risks. Tasks that used to require three people can now be done by one, minimizing the number of people exposed to hazards. There is no longer a need to erect temporary scaffolding or deploy aerial lifts just for measurements, eliminating preparatory work associated with safety measures. Survey staff reported they felt relieved not to have to climb cliffs with lifelines, easing the mental burden on managers as well. The necessity for other workers to wait during surveys was also eliminated, simplifying overall site safety management as a secondary benefit.

Feedback and reactions from clients and inspectors

How did clients react to this new surveying method? During actual inspections, the inspecting officials were initially skeptical about deliverables derived from point clouds captured with a smartphone. However, after reviewing the submitted as-built reports and 3D models, they expressed surprise and reassurance at the measurement accuracy and coverage.

Where previously decisions were made from a limited number of survey points, the ability to visualize the entire slope with point cloud data was highly valued as it meant "nothing was overlooked and the data is reliable." Inspectors could check areas of concern with arbitrary cross-sections and, if necessary, add points themselves to verify errors, enabling flexible inspection. As a result, the time required for as-built confirmation was reduced and the inspection was completed smoothly.

The client municipality also appreciated the contractor’s proactive use of ICT technology. Since this initiative aligned with the national *i-Construction* drive, there is interest in expanding the approach to other work types and sites in the future. In addition to improved site safety management, the enhanced information sharing between client and contractor contributed to strengthening trust through a positive approach to DX.

Ripple effects on the entire construction project after introduction

The benefits of LRTK extended beyond making a single as-built survey easier. The tool was applied to other tasks on site, contributing to overall project efficiency.

For example, scanning the existing terrain before construction improved accuracy in earthwork volume calculations and planning. On this site, the original slope topography was captured in 3D on a smartphone before construction, which helped accurately calculate cut-and-fill volumes compared to the design. This improved quantity management from the initial stage, smoothing cost control and schedule management across the project.

During construction, partial point cloud surveys were also conducted as needed and used for intermediate checks and progress management. Because as-built confirmations that were previously done monthly could be performed more frequently at major milestones, errors and defects could be detected and corrected early, reducing rework.

Furthermore, the acquired 3D data can be used for post-construction maintenance. With the final slope geometry stored in the cloud, future periodic inspections can easily detect long-term deformation by comparing newly scanned point clouds to the original. This data will be useful for future collapse risk assessments and repair planning. The ability to retain point cloud data as an asset that supports aftercare is a major advantage of construction DX.

In this way, the ripple effects of LRTK introduction spread not only within the site but throughout the company. Other site supervisors and technicians came to understand its usefulness, and internal horizontal deployment progressed. The company now holds internal training on LRTK operation, and 3D surveying is becoming commonplace across various civil engineering works, not limited to slopes. A culture of proactively adopting advanced technology has taken root, ultimately enhancing competitiveness and positively affecting bidding.

Conclusion: The future brought by slope surveying DX

DX in as-built slope surveying is creating a virtuous cycle in which safety, productivity, and accuracy all improve. In this case, introducing the smartphone point cloud surveying system LRTK demonstrated that high-accuracy data can be obtained quickly from a safe distance on hazardous slopes, and reporting can be performed seamlessly. Replacing previously routine heavy and dangerous tasks with digital technology is beginning to fundamentally change site management.

Going forward, if such DX technologies are adopted across civil surveying in general, places that were difficult or impossible to measure will steadily decrease. A time is approaching when anyone can easily master 3D scanning and perform as-built and quality management based on data. That means aspects that were previously based on experience or intuition will be visualized, enabling more objective and persuasive construction management.

A future image beyond slope surveying is that common practice at construction sites will shift from "work that involves danger" to "safe work using data." Digital tools can provide solutions to industry challenges such as labor shortages and the decline of veteran technicians. As in the case presented here, accumulating DX at individual sites can be expected to realize a future of safer and more efficient infrastructure construction and maintenance.

Extra: Easy 3D surveying and report integration anyone can start with LRTK

Challenging the conventional notion that "high-precision 3D surveying requires expensive equipment and specialized knowledge," the smartphone surveying system LRTK is changing the landscape. As this case shows, combining a smartphone with a palm-sized GNSS receiver enables anyone to easily measure point clouds with centimeter-level accuracy. No complicated configuration is needed—just press a button in the dedicated app and walk. Positioning and scanning are processed automatically in the background, so even without special skills you can immediately obtain 3D as-built data.

Moreover, LRTK leverages cloud integration to streamline data utilization. Point clouds and photos collected on-site are automatically synced to the cloud, allowing continuation of processing on an office PC or sharing with stakeholders with one click. The cloud includes robust features such as map display of survey coordinates, comparison with design data, and cross-section creation, and even supports automated creation of as-built reports that used to be manual. "Without calling in a specialized surveying team, we can measure, digitize, and complete the report ourselves"—such a future is already being realized with LRTK.

Starting from slope surveying, this smartphone point cloud technology can be widely applied to bridges, tunnels, reclaimed land, and water and sewer management. For those who thought DX tools were difficult and avoided them, LRTK—starting from the familiar smartphone—lowers the barrier to entry. As a means to balance safety-first site operations with productivity improvements, why not give this new 3D surveying experience a try?