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

Introduction: What are the challenges in slope surveying?

A slope (法面) refers to the inclined parts of roads or developed 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 shape (as-built) to verify conformity with the design. However, surveying on steep slopes has posed major challenges in terms of safety, workload, and time. In recent years, driven in part by the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* promotion, digitalization (DX) of construction sites has attracted attention, and new solutions are needed to overcome the limits of conventional slope surveying methods. There have been reported cases of falls and near-miss incidents during slope surveying, so improvements have been sought not only for productivity gains but also to ensure worker safety. This article organizes the issues of conventional slope as-built surveying and, through a case study of on-site introduction of the smartphone-based 3D surveying system LRTK, concretely presents the points that led to improvements in productivity and safety.

Limits of Conventional Methods: Danger, Man-hours, and Documentation Burden

Conventional slope as-built surveying has been criticized for the following issues.

• Danger: Surveyors had to enter steep slopes to use tape measures or staffs, or climb scaffolding installed on the slope to take measurements. There was always the risk of falls or falling rocks, imposing a heavy burden on safety management. Although aerial work platforms were sometimes used, in narrow mountainous areas vehicles could not always be brought alongside, making such measures impractical in some cases.

• Workload: On steep terrain, simply acquiring each survey point took significant time. Teamwork with multiple people and the placement of safety personnel for high work were necessary, requiring many personnel and man-hours. For large slopes, the surveying itself could take half a day to several days.

• Documentation burden: Based on the heights and slopes of points obtained on site, drawings and as-built control tables had to be created manually. Organizing numerous survey points, calculating errors relative to design values, and compiling them into the prescribed formats was tedious. If points were missed, crews had to return to the site, which placed a heavy burden on site supervisors and surveying technicians.

Background of LRTK Introduction: Trigger and Selection Reasons

At one slope construction site facing the above issues, ensuring safety and improving efficiency in as-built surveying became urgent. In fact, there was a near-miss incident where a worker slipped during conventional surveying, and the site supervisor sought a non-contact, safe measurement method. With limited personnel and schedules to meet, labor-saving and speeding up of surveying work 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 attaches a compact RTK-GNSS receiver to a commercial smartphone and uses the phone’s camera and LiDAR to scan the surroundings, enabling acquisition of high-accuracy 3D point cloud data. Unlike conventional drone photogrammetry, it does not require flight permits or large-scale equipment, and the ability to measure solo in a short time was highly regarded, so a trial introduction was decided. Of course, the client was informed of the new method in advance and consented to its conformity with as-built management procedures and the format of deliverables before the trial.

The decisive factors were that it was low-cost and easy to operate. The fact that anyone on site could use it without purchasing an expensive laser scanner or arranging a specialist operator was valued. As described below, LRTK also links with a cloud service, enabling point cloud data sharing and automatic creation of as-built documents, which promised efficiency in preparing submission materials for the client.

Implementation Process: From Preparation to Field Operation

Let’s briefly follow the flow from preparation to actually conducting surveying with LRTK.

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

• Field surveying: On the survey day, a 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 the smartphone aloft and walked to scan the entire slope. Complex terrain was captured as a 3D point cloud down to the corners 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-accuracy point cloud model was generated on LRTK’s cloud service, and office PCs could access the data instantly. The point-cloud processing software that was traditionally required was unnecessary, so once scanning was completed on site, the as-built 3D model was nearly finished.

• Document creation and utilization: From the cloud point cloud data, required cross-sections and dimensions could be obtained immediately. For example, overlaying the design cross-section with the measured point cloud to check slope thickness or gradient was easy with a button click. Since measurement values required for as-built management documents were also automatically calculated, the person in charge only had to verify and print them, and as-built documentation was completed. The point cloud itself could be shared with the client, allowing the finished condition—difficult to convey with paper drawings alone—to be intuitively shown in 3D.

Results Achieved: Reductions in Survey Days, Personnel, and Documentation Time

Using LRTK produced greater efficiency than expected. Here are some concrete results.

• Shortened survey days: Sites that previously required a total of 1–2 days for slope as-built surveying completed the task within half a day after introducing LRTK. For example, even a slope 50 m (164.0 ft) long with a height difference of 30 m (98.4 ft) could be measured on site in about an hour in the morning, and as-built data could be organized the same day (a 75% reduction in work time).

• Reduced required personnel: Previously, surveying required a surveyor plus 2–3 assistants (3–4 people total), but non-contact measurement with LRTK is basically completed by one person (even when a safety watch is required, about 2 people). With a significant reduction in manpower, personnel could be reallocated to other construction tasks, improving productivity of the whole site.

• Reduced documentation time: By using as-built dimensions automatically calculated from the point cloud data, the time to prepare reports was dramatically shortened. What used to take half a day (over 4 hours) to organize survey points, create drawings, and transcribe tables now only requires about 30 minutes of data checking and outputting after LRTK introduction. This reduced administrative burden allowed survey staff to allocate more time to quality control tasks.

Perceived Safety Improvements: Non-contact Measurement of Hazardous Areas and Reduced Staffing

Site staff strongly felt the safety benefits of this introduction. The greatest effect was that people no longer had to enter dangerous steep slopes. Previously, there were occasions when workers had to don lifelines and climb the slope, but LRTK allows surveying from distant safe zones. Even on fragile cliffs or places at risk of collapse, the current condition can be grasped non-contact, contributing to reduced risk of secondary disasters.

Additionally, reduced staffing lowered exposure to site risks. Tasks that previously required three people could be completed by one, minimizing the number of personnel exposed on site. There was also no longer a need to erect scaffolding or deploy aerial work platforms solely for measurement, reducing preparatory safety work. Survey staff commented, “It’s reassuring that we don’t have to climb cliffs with lifelines anymore,” which eased managers’ psychological burden as well. The elimination of the need for other workers to wait during surveying simplified overall site safety management, a beneficial side effect.

Client and Inspector Evaluation and Reactions

How did clients respond to this new surveying method? At inspections, the inspector in charge was initially skeptical about the unfamiliar deliverable of a point cloud obtained with a smartphone. However, upon reviewing the submitted as-built documents and 3D model, they expressed surprise and reassurance at the measurement accuracy and comprehensiveness.

Whereas acceptance had previously been decided based on a limited number of survey points, the ability to visualize the entire slope with point cloud data was highly valued as “no omissions and trustworthy.” Inspectors could check points of concern in arbitrary cross-sections and, if necessary, add their own measurement points to verify errors, enabling flexible inspection. As a result, the time required for as-built verification was shortened and inspections were completed smoothly.

The client municipality also appreciated the contractor’s proactive use of ICT. As an initiative aligned with the national “i-Construction” drive, there are expectations for expansion to other work types and sites in the future. The improved on-site safety management and enhanced information sharing between client and contractor contributed to strengthening trust and demonstrated a positive stance toward DX.

Spillover Effects on Overall Construction after Introduction

The benefits of LRTK were not limited to making a single as-built survey easier. The tool was applied to other tasks on site, contributing to overall construction efficiency.

For example, scanning the existing terrain before construction improves accuracy in earthwork quantity calculations and construction planning. In this project, the original terrain of the slope was 3D surveyed by smartphone before starting work, aiding accurate calculation of cut-and-fill volumes by comparison with the design. This increased quantity management accuracy from the initial stages, smoothing cost and schedule management for the entire project.

During construction, partial point cloud surveys were conducted as needed and used for intermediate inspections and progress management. Because as-built confirmation, formerly done monthly, could be performed frequently at major stages, errors or defects were detected early and corrected, reducing rework.

Furthermore, the acquired 3D data can be used for post-construction maintenance. With the final slope shape data stored in the cloud, comparing newly scanned point clouds during periodic inspections years later makes it easy to grasp long-term changes. This data will be useful for future collapse risk assessments and repair planning. Being able to retain point cloud data as an asset that looks beyond construction to aftercare is a major advantage of construction DX.

Thus, the ripple effects of LRTK adoption extended beyond the site to the company as a whole. Other site supervisors and engineers learned of its usefulness, and horizontal deployment within the company progressed. Now, LRTK operation training is conducted in internal training, and 3D surveying is becoming common in various civil engineering projects beyond slopes. A corporate culture positive toward advanced technologies has taken root, ultimately enhancing competitiveness and positively affecting contract acquisition.

Conclusion: The Future Vision Brought by Slope Surveying DX

DX in slope as-built surveying is creating a virtuous cycle in which safety, productivity, and accuracy all improve. In this case, the introduction of the smartphone point cloud surveying system LRTK demonstrated that high-precision data can be obtained quickly from a safe distance on dangerous slopes and reporting can be done seamlessly. By replacing the heavy and dangerous work that was once taken for granted with digital technology, site management is beginning to change dramatically.

If such DX technologies spread across not only slope surveying but civil surveying in general, places that were difficult or impossible to measure will steadily decrease. An era is near in which anyone can easily perform 3D scanning and conduct as-built and quality management based on data. That means aspects previously dependent on experience and intuition will be visualized, enabling more objective and persuasive construction management.

A future vision beyond slope surveying includes the shift of site norms from “work that involves risk” to “safe work using data.” Digital tools can provide solutions to industry challenges such as labor shortages and the decline of veteran technicians. By accumulating DX efforts on each site as in this case, we can expect a future of safer and more efficient infrastructure construction and maintenance.

Bonus: Simple 3D Surveying and Document Integration Anyone Can Start with LRTK

Challenging the conventional wisdom that “high-precision 3D surveying requires expensive equipment and specialist knowledge,” the smartphone surveying system LRTK is changing the game. As introduced here, combining a smartphone with a palm-sized GNSS receiver enables anyone to easily perform point cloud measurements with cm level accuracy (half-inch accuracy). No complicated settings are required—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, by leveraging cloud integration, LRTK smooths the utilization of acquired data. Point clouds and photos collected on site are automatically synchronized to the cloud, and continuing processing on an office PC or sharing with stakeholders is just one click away. The cloud provides rich functions such as map display of survey coordinates, comparison with design data, and cross-section creation, supporting even the automatic creation of as-built documents that used to be manual. “Without calling a specialist surveying team, we can measure, digitize, and complete reports ourselves” — that future is already being realized by LRTK.

This smartphone point cloud technology, which began with slope surveying, can be applied widely to bridges, tunnels, developed land, and water and sewer maintenance. For those who have shied away from DX tools as seemingly difficult, starting with the familiar smartphone and LRTK lowers the barrier. As a means to balance safety-first site operation with productivity improvement, why not try this new 3D surveying experience at least once?