Challenges of Pile Driving Work: Ensuring Accuracy and Labor Shortage

In pile driving work, which forms the foundation of civil engineering and construction projects, millimeter-level precise positioning is required. Traditionally, the marking of pile locations (layout marking) was performed on-site by surveying technicians based on coordinates from the drawings; they would mark the ground or drive wooden stakes as markers, and heavy equipment operators relied on these to carry out work. However, this method requires manpower and time, and carries the risk of errors. For example, insufficient communication between the surveying personnel and the operator can cause position shifts, or if temporary marker stakes move during work it will affect construction accuracy. Also, in locations where it is physically difficult to install markers, such as steep slopes or areas by water, achieving accurate positioning was inherently difficult.

At some large-scale sites, machine guidance that equips heavy equipment with GNSS (satellite positioning) has begun to be introduced, but dedicated high-precision equipment is very expensive and has not become widespread at small- and medium-sized sites. As a result, ensuring accuracy in pile driving has become an issue at many construction sites. Traditional analog surveying using transits and tape measures is time-consuming and lowers productivity. It is not uncommon for setting out pile positions to take half a day, and sites have been seeking more efficient and reliable methods for guiding pile driving.

Increased difficulty of positioning in the top-down construction method

In urban underground works and similar projects where the top-down construction method (top-down method) is increasingly being adopted, setting out pile positions becomes even more difficult. The top-down construction method is a technique in which the above-ground frame is built first, and the underground structure is constructed sequentially from the upper floors down to the lower ones, offering the advantage of allowing aboveground and underground work to proceed in parallel within a limited construction period. However, the underground columns and foundation piles placed early in the construction become permanent members that support later structures, so even deviations of a few millimeters (a few hundredths of an inch) in the position of each individual pile are unacceptable.

At top-down construction sites, survey work must be carried out surveying in confined spaces covered by the first-floor slab and intermediate slabs, making it difficult to secure line of sight. Unlike conventional methods with the ground largely open, it is hard to set reference lines with adequate clearance or to position surveying instruments at a distance. In urban areas surrounded by high-rise buildings, securing locations to set up surveying equipment is also difficult, and satellite positioning is often obstructed. Moreover, because aboveground and underground work proceed simultaneously, there is pressure that there is no time for rework, and a single surveying-point error can have a ripple effect across the entire construction process. In fact, on one large site, multiple surveying teams double-checked the same pile layout and proceeded with construction only after confirming their results differed by no more than a few millimeters. To succeed in top-down construction, how reliably and quickly surveying and layout tasks can be performed is the key.

RTK positioning and AR technology opening a revolution in pile-driving layout

A key technology attracting attention for solving these issues is RTK positioning. RTK (Real Time Kinematic) is a technology that corrects errors in satellite positioning (GNSS) in real time using correction data from a base station, allowing positions to be determined with an accuracy of a few centimeters (a few inches). Simply put, it is an “ultra-high-precision GPS usable on site,” and it makes it possible to match the coordinates on design drawings and the actual on-site positions almost exactly. For example, if you specify the coordinates of the point where a pile should be driven with an RTK-capable device, you can guide the pile to the location indicated by the device, drastically reducing errors compared to conventional methods.

Surveyors traditionally performed setting-out with tape measures and transits, but with RTK you can navigate directly to the target coordinates, eliminating the intermediate setting-out process. Improving construction accuracy through GNSS utilization is an important theme in the Ministry of Land, Infrastructure, Transport and Tourism's advocated "ICT construction" and "i-Construction." By incorporating RTK into pile-driving guidance, it becomes possible to place piles with the same accuracy for anyone, without relying on the intuition and experience of skilled workers. For heavy equipment operators, attaching a receiver to the machine or the pile and seeing real-time deviations from the target position allows them to carry out pile-driving work safely and reliably while monitoring the display at hand. High-precision positioning with RTK is thus revolutionizing pile-driving guidance (navigation to pile positions).

Effortless high-precision stake-out enabled by smartphone surveying and LRTK

In recent years, smartphone surveying, which makes it easier to take advantage of RTK, has emerged and brought significant changes to worksites. Smartphone surveying, as the name implies, is a method of using a smartphone as a surveying instrument; by simply attaching a dedicated small RTK-GNSS receiver to the smartphone, centimeter-level positioning becomes possible. For example, the device called LRTK Phone, developed by a venture company originating from Tokyo Institute of Technology, transforms a commercially available smartphone into a pocket-sized high-precision surveying instrument simply by attaching a small receiver weighing approximately 165 g. Because it can be used anywhere as long as there is power and a smartphone, the era in which each field worker can carry a high-precision positioning device—one device per person—has become a reality.

The benefits of smartphone surveying are immeasurable. First, the operation is intuitive and easy. Because the dedicated app displays the current position and target points on a map, it is easy for workers without specialized knowledge to use. Next, there is improved work efficiency. Marking stake positions that used to require calling a surveying team can now be done by the workers themselves with just a smartphone. By sharing design coordinate data in advance via cloud integration, a system can also be implemented that guides workers to the target point on site just by pressing a button in the app. Furthermore, because positioning results and construction records can be shared to the cloud from the field instantly, the reporting work after returning to the office is greatly simplified. In other words, by adopting smartphone surveying, anyone on site can identify stake-driving positions "anyone, immediately, and accurately," leading to a dramatic improvement in productivity and construction accuracy.

Small smartphone surveying devices are also highly effective in disaster sites. Even in disaster-stricken areas where communication infrastructure has been severed, LRTK devices can directly receive centimeter-level correction information (cm level accuracy (half-inch accuracy)) (CLAS) transmitted from Japan's Quasi-Zenith Satellite "Michibiki" and continue high-precision positioning. In fact, during the 2023 Noto Peninsula earthquake, LRTK was used for field surveys in environments where base stations were down, making a major contribution to rapid surveying under difficult conditions.

High-precision coordinate navigation that guides you to stake positions without getting lost

The smartphone surveying app is equipped with a coordinate navigation function that allows anyone to reach the target point without getting lost. Simply select in the app the coordinates of the stake positions you previously registered in the cloud and instruct “go to this coordinate,” and the screen will display the direction and distance to the destination in real time. As you approach the destination, the display switches to a precision guidance mode resembling a crosshair target, allowing fine adjustments down to within a few centimeters (a few inches). By aligning the device position according to the blue arrows and guide indicators, you can stand precisely on the stake placement point. Because positions can be identified via intuitive on-screen guidance without special skills, wasted movement and alignment are reduced, enabling one person to efficiently mark out multiple stake positions in succession. In actual fieldwork, there are reports that stake marking using the latest GNSS×AR guidance was completed in about 1/6 of the time compared to traditional optical surveying. For example, on a certain bridge pier foundation project, stake positioning that used to take half a day was completed in about 1 hour with the introduction of smartphone RTK guidance, significantly shortening the working time.

ARで見える杭位置：仮想杭による直感的な確認

Using a smartphone's AR (augmented reality) function, you can intuitively confirm the positions where piles will be driven through the camera. A virtual pile model (AR pile) can be overlaid on on-site footage to visualize a marker that shows "a pile will be installed here." Even in places where it is not possible to physically drive wooden piles, the virtual pile appears on the smartphone screen, making it easier to share position information with operators and nearby workers. For example, in reinforcement work on steep slopes, a smart procedure has been practiced in which an AR pile is placed from a safe, distant location to identify the position, and the ground directly beneath it is excavated and the pile is driven. In this way, the function of designating a target point through the camera and acquiring coordinates—subject positioning—makes it possible to determine pile positions even from a distance. Even in locations that were traditionally difficult to mark, such as waterfronts or concrete surfaces, AR displays can indicate "a pile is here," enabling visual positioning.

AR also helps with preliminary reviews of construction plans. If you load BIM/CIM and other completed model of a structure onto a smartphone, you can project it onto the real site at its coordinate position so all stakeholders can share the finished-image. Because LRTK continuously measures the user’s position with high accuracy, the model’s position does not shift even when workers move. It also makes it easy to overlay design data from drawings onto the site space to perform clash checks and to have everyone confirm construction procedures. Using AR to integrate digital information into the site can contribute not only to verifying pile-driving positions but also to the overall DX (digital transformation) of construction.

Application of point cloud scanning to as-built management

By combining a smartphone LiDAR scanner with RTK, it is also possible to record a site as highly accurate 3D point cloud data. Scanning with a regular smartphone alone tends to produce positioning errors and distortion, but by walking while LRTK continuously corrects your position to centimeter-level (cm level accuracy (half-inch accuracy)), you can assign accurate coordinates to the acquired point cloud. With just a smartphone in your pocket you can scan the existing terrain and structures entirely and perform tasks on the spot such as measuring the distance between any two points and measuring volumes. There is no need to bring a dedicated laser scanner or PC to the site, and in-house staff can easily perform 3D measurement and quantity calculation, improving efficiency for verifying earth embankment volumes and as-built inspection. The acquired point cloud data can be uploaded and shared to the cloud immediately, so the 3D situation can be viewed remotely via a browser.

Furthermore, LRTK is also equipped with a function that automatically attaches high-precision position coordinates and orientation information to captured photos and accumulates and manages them as a time series. It is also possible to link photos to their capture locations on the point cloud data and display them; for example, you can save bridge crack locations together with the point cloud model and photographs. You can also overlay a 3D model of the construction plan with the point cloud to compare them and automatically calculate the difference in earthwork volume from the discrepancy between the design and the current conditions. With these functions, consistent data utilization with a single smartphone becomes possible, including post-pile-driving as-built management and report preparation. The role of smartphone surveying in promoting the digitization of overall field operations will be very significant.

Benefits of Labor Reduction and Eliminating the Need for Skilled Workers on Site

The effects of labor reduction and no need for specialized skills brought by the latest smartphone surveying solutions provide significant advantages to site operations. Intuitive guidance enables even novice workers to set stake positions with accuracy comparable to veterans, so layout work no longer depends on specific skilled personnel. As a result, this contributes to resolving labor shortages and reduces the hassle of calling in specialized staff from other departments for surveying. Because one person can complete everything from surveying to marking stake positions, it also leads to personnel allocation optimization and simplification of work procedures. In addition, since workers are less often required to signal near heavy machinery, it also contributes to improved safety.

Furthermore, the low cost and ease of use also encourage wider adoption. Compared with conventional high-precision GNSS equipment that used to cost several million yen, the combination of a smartphone and a compact receiver has a lower barrier to entry. Because it can be operated on a smartphone people are already familiar with, there is little need to learn how to use a new dedicated device from scratch. This approachable ease of use and price point make it easy for small and medium-sized enterprises and small-scale construction projects to adopt. When each technician has a high-precision positioning tool and everyone on site can utilize digital data, it raises construction quality and at the same time leads to work-style reform.

Conclusion: Digital transformation of layout work starting with LRTK

Traditional stakeout has long been plagued by issues of accuracy, time, and manpower, but the new approach introduced in this article—smartphone × RTK × AR—is significantly improving those areas. Even without relying on surveying teams, anyone on site can perform high-precision positioning, and the quality and productivity of stake installation will dramatically increase. Although there are constraints due to factors such as satellite reception conditions and considerations for equipment management, overall smartphone surveying combined with RTK guidance is set to become the new standard on job sites. The revolutionary approach of "guiding stake placement with a smartphone" is bringing an era in which anyone can place stakes without mistakes within reach.

The main advantages of this technology can be summarized as follows.

• Improved construction accuracy: Always guide pile positions with errors within a few cm (a few in). This minimizes the discrepancy between design coordinates and actual pile locations, improving structural quality and safety. It also prevents accumulation of errors in foundation work involving a large number of piles.

• Dramatic improvement in work efficiency: Intuitive guidance using RTK and AR drastically reduces the time required for staking out positions. A single worker can quickly measure points, enabling workforce reductions and simplified setup. It also reduces wasted time on moving and aligning.

• Easy low-cost adoption: Cheaper than conventional expensive surveying instruments and able to leverage existing smartphones, requiring almost no new operational training. Equipping one device per person becomes realistic even on small- and medium-sized sites.

• Versatility and contribution to DX: Can be used widely not only for pile-driving guidance but also for as-built surveys and construction quality management. The same data is useful for downstream processes and maintenance, contributing to the digitization of the entire site.

Such high-precision smartphone positioning system LRTK is already beginning to deliver results at construction sites across the country and is attracting attention as an optimal solution for the i-Construction era. If you have concerns about conventional positioning work, consider introducing LRTK-based simple surveying at your sites to realize DX for pile-driving operations. Details are also available on the [LRTK official site](https://www.lrtk.lefixea.com). Let’s harness cutting-edge technology on site and advance the development of next-generation worksites where anyone can perform construction accurately and efficiently.