The Future of Slope Greening Construction Visible with AR

Slope greening construction is an important type of work that covers slopes such as roadsides, levees, and reclaimed land with vegetation to improve the landscape, prevent landslides, and conserve the environment. However, because work is performed on steep slopes and terrain can be complex, there are many challenges from design through construction to post-completion management. In recent years, DX (digital transformation) in construction sites has created new approaches to solving these challenges. One technology attracting particular attention is the use of AR (augmented reality) accessible via smartphones and similar devices. This article reviews the on-site challenges of slope greening construction and introduces how AR is changing the future of construction.

What is slope greening construction

Slope greening construction is work that applies vegetative cover to artificially created slopes or natural slopes. Specifically, various methods are used depending on terrain and soil, such as hydroseeding—spraying a slurry of topsoil mixed with seed and nutrients known as vegetation substrate spraying (so-called seed spraying)—laying and fixing vegetation mats that incorporate seeds into fiber mats (vegetation mat method), planting seedlings at regular intervals (planting work), and broadcasting seed (seeding work). These methods introduce greenery to otherwise inorganic concrete or cut slopes, aiming to improve the landscape, prevent erosion from rain, and restore ecosystems. While slope greening plays an important role from the perspectives of environmental consideration and disaster prevention for social infrastructure, its design and construction require high levels of expertise.

Challenges in slope greening construction

First, we outline the representative challenges that field engineers face in design, construction, and management of slope greening. Because this work deals with steep slopes, it has difficulties not seen in other trades at each stage. The main points are listed below.

• Design-stage challenges: It is not easy to grasp slope shape and the surrounding environment from drawings alone. Traditionally, gradient and greening areas are examined based on plan views and cross-sections, but with complex terrain, it can be difficult to share the finished image among stakeholders, and conveying design intent can take time. Also, planned details on drawings may not match actual terrain, forcing changes during construction. Particularly, elements that are easy to overlook on drawings—such as undulations of the slope or interfaces with surrounding environments—often emerge later, requiring plan revisions.

• Construction-stage challenges: Work on steep slopes has many physical constraints, and carrying out construction exactly as designed can itself be difficult. Attention must be paid to worker safety and to transporting and securing materials and equipment, and errors tend to occur in staking out (batter boards) and laying materials. On large slopes, it is also difficult to accurately understand on-site “where what is to be constructed,” creating risks of omissions or duplications in construction due to human error. Many tasks must rely on on-site judgment, raising concerns that quality depends on the experience and intuition of those in charge.

• Construction management (as-built verification) challenges: Verifying after completion whether work was finished according to design—known as as-built management—is also a major burden. Inspecting the slope’s overall gradient and covered area requires many measurement points, and conventionally required using surveying instruments to measure heights point by point, which took time. Moreover, measurements at height are dangerous, so the number of measurement points could not be increased indiscriminately, often resulting in inspections that lack comprehensiveness. Because measurement points are limited, oversights can occur, and there is also the burden of bringing measured data back to the office to compare with drawings. Even if problems exist, they may not be noticed immediately on site, causing rework to lag and extra costs to be incurred.

Sharing design images and forming consensus before construction

To address these challenges, visualizing the finished image with AR before construction is effective. By creating a design model (3D model) of the slope greening in advance and holding a smartphone or tablet on site, the completed greening state can be overlaid on the actual slope through the camera. For example, one can intuitively check on site which positions the vegetation mats to be laid will cover, or how far the area to be greened by spraying will spread. This allows all stakeholders on site to share the finished image of slope greening—previously only imaginable from drawings or perspective renderings. Preventing image gaps and aligning recognition early among clients, designers, and construction personnel enables smooth, irreversible consensus formation. Because the finished image is easy to share, it also helps build external consensus with local residents.

In practice, on one site where a greening plan model was overlaid on the slope using smartphone AR, the client praised that “the finished shape I couldn’t grasp from the drawings was clear at a glance.” A veteran construction management engineer remarked, “This allows confirmation without relying on experience,” and pre-construction meetings became smoother. AR-based information sharing has revitalized on-site communication, resulting in improved quality and efficiency.

The significance of experiencing elevation differences and spatial relationships with AR

One advantage of AR visualization is that you can experience height and distance on site. Slopes on plan drawings are shown only as two-dimensional lines and numbers, but in the field they have absolute heights and gradients that far exceed human height. By viewing a video with the design model overlaid in AR, one can intuitively grasp elevation differences that are hard to perceive from drawings. For example, you can confirm at true scale “up to how many meters this vegetation mat will be laid” or “how much higher the upper edge of the vegetated area is than where I am standing,” which helps in considering safety measures and construction methods.

AR also makes the positional relationships among design elements obvious. Boundaries between multiple greening methods (such as seed spraying and planting bands) and clearance distances to nearby structures can be checked on site, allowing verification in advance whether each operation can be placed as planned without interference.

Improving as-built verification accuracy with point cloud scanning × AR

AR is also powerful for as-built management to confirm post-construction quality. Recently, it has become easy to acquire the entire slope’s shape as point cloud data and to model it in 3D using drones, laser scanners, and high-performance smartphones. After constructing a slope, scanning it with a smartphone’s LiDAR or photogrammetry records the finished surface’s undulations as a collection of millions of points called a point cloud. For example, for a slope about 100 m (328.1 ft) in total length, you can scan the entire slope in a few minutes simply by walking while holding up a smartphone, which is overwhelmingly more efficient than traditional point-by-point surveying. Because point cloud data contains real X, Y, Z coordinates (positional information), it can be overlaid with the 3D model from design (or a predicted finished terrain created from design drawings) to analyze differences. For instance, by comparing the design model and the as-built point cloud and creating a color-coded heat map of height excesses and deficiencies, you can see at a glance which areas are raised higher than design and which are lower. Displaying this heat map or point cloud model in AR on site enables precise identification of where discrepancies occur on the actual slope. With centimeter-level high-precision AR overlay (half-inch accuracy), construction defects are not overlooked and corrective work can be started immediately on the spot. Conventional as-built inspections that once took days from point-by-point measurement to report creation can, with this workflow, produce instant on-site results and dramatically streamline the inspection process. The Ministry of Land, Infrastructure, Transport and Tourism is also promoting the spread of as-built management using such 3D utilization, and point cloud measurement combined with AR is likely to become a new standard going forward.

For example, in one slope project an area with insufficient spray thickness was discovered immediately by an AR heat map and corrected by additional spraying the same day. Under conventional methods, defective areas might have been discovered only after inspection, requiring reinstallation of scaffolding and redo work, but immediate checking with point cloud + AR prevented such waste. In this way, combining AR with point cloud measurement brings a rapid PDCA cycle to the site.

Smooth information sharing through cloud integration

To maximize AR and point cloud data, data integration via a cloud platform is indispensable. Traditionally, design drawings and survey data were exchanged on paper or by e-mail and managed separately at the site and the office, leading to communication errors such as the latest drawings not reaching the site or site changes not being communicated to designers. Using the cloud, 3D models and construction conditions created at the design stage can be uploaded and shared with the site in advance. Construction personnel can call up the latest data from a smartphone at any time and display it in AR, allowing construction to always be based on the latest information. Conversely, point cloud scans and as-built records obtained on site are saved to the cloud on the spot, enabling clients and designers to check progress and provide advice from the office. For example, a heat map automatically generated from as-built point clouds can be shared via the cloud with stakeholders so they can issue real-time instructions such as “reduce this area because the fill is too thick.” Centralized cloud data management helps bridge information gaps between clients, designers, and construction sites, reducing rework and conflicts due to misunderstandings. Some cloud systems also have functions to automatically generate forms from acquired data, reducing the burden of creating inspection documents and reports. Accumulated 3D data can also be used for future maintenance and improvement work. Comparing past as-built data with current conditions makes it easier to identify aging changes and repair locations, aiding long-term infrastructure management.

Lightweight and fast: useful for small sites and disaster recovery

AR construction support tools are not limited to large-scale projects. Precisely because they are lightweight systems utilizing smartphones, they are highly effective for small sites and disaster recovery situations that require rapid response. In the past, introducing ICT in small-scale projects in areas where arranging 3D surveying equipment and specialist operators was difficult posed high barriers. But with smartphone + AR, anyone can quickly take the tool into the field, making it easier for local governments to adopt for simple repairs of road slopes they manage or for small private land greening projects. In disaster recovery sites such as slope collapses from heavy rain or earthquakes, rapid situational assessment and planning are required. For example, one can measure a collapsed slope on the spot with a smartphone, calculate the collapsed soil volume from a point cloud model, and immediately share a post-repair greening plan in AR with stakeholders. A mobile, on-site solution is particularly useful for small sites or disaster response where large numbers of machines or personnel cannot be deployed. In fact, some municipalities and construction companies have begun using smartphone AR in disaster recovery sites, contributing to faster initial responses.

Start AR construction management with a smartphone: the potential of LRTK

Finally, as a concrete solution to realize these AR technologies on site, we introduce LRTK. LRTK is a positioning device that attaches a compact high-precision GNSS antenna to a smartphone, transforming a phone into a survey instrument with centimeter-class accuracy (half-inch accuracy). Compared to conventional dedicated surveying instruments, it can be introduced at lower cost, making it realistic for site staff to carry one device each. With this single device, a wide range of functions are available, from measuring current position to 3D point cloud scanning and AR overlay of design models. No complex setup or specialized skills are required—simply attach it to the smartphone and launch the dedicated app, and anyone can use it. It is designed to be intuitive so veteran technicians unfamiliar with IT can also use it without confusion.

• High-precision positioning and point cloud acquisition: Using LRTK, you can obtain high-precision point cloud data with absolute coordinates simply by scanning the surroundings with the smartphone’s camera or LiDAR. Measuring the shape of slopes is completed not by traditional manual surveying by skilled technicians but by walking the site and capturing it with a smartphone. From the acquired point cloud, calculations such as earthwork volumes and cross-section creation can be executed automatically on the spot, dramatically shortening the time from surveying to design review.

• AR overlay display: Based on the precise positional information obtained with LRTK, design drawings and 3D models can be accurately overlaid on the real landscape. The slope greening construction plan discussed here can be projected on site from models uploaded to the cloud in advance, allowing an accurate image of the finished product. It is also possible to display in AR a heat map visualizing differences between as-built point cloud data and the design model, directly preventing overlooked defects.

• Construction navigation (staking support): An AR navigation function is also available to indicate points and lines defined in the design on site. For example, you can virtually draw contour lines or construction area lines on the slope or place virtual markers where piles should be driven. This allows staking and batter board tasks, which used to be difficult for surveying teams, to be done accurately and quickly by a single person. Even on steep slopes where direct entry is difficult, you can instruct and confirm points on AR from a distance, contributing to improved safety.

By utilizing LRTK in this way, you can seamlessly perform planning, as-built management, and surveying for slope greening construction with just a smartphone. Site DX can start from familiar tools without major capital investment. Trials of smartphone AR are already progressing on small and medium-sized construction sites, and the use of digital technologies in the slope greening field is steadily expanding. Try simple 3D surveying and AR display with a smartphone and LRTK. Communication and quality control on slope greening sites will improve dramatically, providing unprecedented efficiency and peace of mind. The future of slope greening construction is steadily being opened by such digital technologies. Make the latest AR surveying technology your ally and take the step toward safer, more efficient sites. If smartphone AR devices become standard on sites, the way slope greening construction is carried out will be greatly transformed. What AR makes visible—what could not be seen before—is precisely the future of slope greening construction.