Supporting Pile-Driving Work with GNSS Receivers ─ Streamlining Construction with High Precision

Importance of Piling Work and Traditional Challenges

In piling work that forms the foundation in civil engineering projects, placing piles in the correct positions is paramount. Traditionally, surveyors set out positions on site based on coordinates on drawings, marking the ground (making marks) or driving wooden stakes as reference points, and heavy equipment operators relied on these to install piles. However, this method tends to be labor- and time-intensive and carries a risk of errors. For example, if communication between the surveyor and the workers is insufficient and positions shift, or if the reference stakes move, construction accuracy is affected. Also, on slopes or waterside areas where it is physically difficult to install markers, staking out positions itself is challenging.

On large sites, machine guidance systems equipped with GNSS (satellite positioning) have begun to be introduced on heavy equipment, but the dedicated equipment is expensive and has not yet spread to small and medium-sized sites. As a result, ensuring piling accuracy remains a challenge at many construction sites. Traditional optical surveying for staking out pile positions was time-consuming and a factor that hindered productivity (it has been reported that conventional surveying methods took about six times longer than the latest technologies). Against this background, the field has been demanding more efficient and accurate methods for guiding pile driving.

The value GNSS receivers bring to stakeout

One of the keys to solving this challenge is RTK positioning technology. RTK (Real Time Kinematic) is a technology that corrects satellite positioning (GPS and GNSS) errors in real time using correction information from a base station, enabling position determination with centimeter-level accuracy (half-inch accuracy). Simply put, it's "a highly precise GPS usable on site." With RTK positioning, it becomes possible in stakeout operations to match the coordinates on the design drawings exactly with the actual on-site positions. For example, if you program the coordinates of the points where stakes should be driven into an RTK-capable device, guiding personnel on site to the positions indicated by that device can minimize deviations in stake locations.

Traditionally, surveyors used tape measures and transits (optical surveying instruments) to determine pile locations, but with RTK you can navigate directly to target points on survey data, eliminating intermediate staking-out work. In the "ICT construction" and "i-Construction" initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism, improving construction accuracy using GNSS is a key theme. By incorporating RTK into pile-driving guidance, reliance on skilled workers' intuition is reduced, enabling anyone to place piles with the same level of accuracy. For heavy equipment operators, real-time information from receivers mounted on the vehicle or the pile that shows the offset between their position and the target position allows them to perform pile-driving while monitoring a local display, improving safety and reliability. RTK positioning technology is thus revolutionizing pile-driving guidance (navigation to pile positions).

How smartphone integration and the cloud are changing construction sites

In recent years, "smartphone surveying," which makes it easier to utilize RTK positioning, has emerged and is bringing significant changes to construction sites. Smartphone surveying, as the name suggests, is a method of using a smartphone as a surveying instrument. By simply attaching a dedicated compact RTK-GNSS receiver to a smartphone, centimeter-level positioning—previously requiring specialized equipment—becomes possible. For example, a device called "LRTK Phone," developed by a startup, turns an iPhone into a pocket-sized surveying instrument simply by attaching a receiver weighing about 165 g, allowing it to be carried anywhere and used as needed. This has ushered in an era in which everyone on site can carry a high-precision positioning device of their own.

The benefits that smartphone surveying brings are immeasurable. First, the operation is intuitive and simple. Because the smartphone app displays the current position and the target point on the screen, it is easy for workers without specialized knowledge to use. Second, increased efficiency. Tasks that used to require calling a surveying team to set out positions can now be handled by the workers themselves with just a smartphone. If design coordinate data is shared in advance via cloud integration, a system can be realized that guides users to the target point by simply pressing a button on site. Furthermore, because positioning results and construction data can be uploaded and shared to the cloud in real time, reporting work after returning to the office is also simplified. In short, by introducing smartphone surveying, pile-driving positions can be identified “by anyone, immediately, and accurately,” and improvements in site productivity and pile-driving accuracy can be expected.

Accurate positioning guidance with GNSS for a single operator

When coordinate navigation by GNSS becomes available, the task of guiding stakeout positions can be performed by a single person. In conventional layout work, at least two people were required: a surveyor handling a total station or tape measure, and a worker marking the stake positions. However, if a worker carries a high-precision GNSS device, they can be guided to an exact point and mark it alone. By following the arrows and distance readout on a smartphone screen, there is no need to ask others for instructions.

Furthermore, the visual guidance function provided by AR (augmented reality) also strongly supports solo work. Because a virtual target marker is displayed through the smartphone camera, workers can intuitively grasp the discrepancy between their position and the target point. Even if they are not directly above the target point, they can make fine adjustments while confirming on the camera the image of “the stake is there.” Also, if there is a function that alerts by sound or vibration upon approach, they can tell they are close to the point even when looking away from the screen. In this way, with GNSS position guidance, a single person can stake out positions with accuracy comparable to conventional methods. Not only does this lead to a reduction in personnel, but precise AR navigation also reduces unnecessary movement and rework, allowing work to proceed efficiently. From the heavy equipment operator’s perspective, there is also the advantage of increased safety because a guide does not need to stand nearby.

On-site application examples using LRTK (guidance accuracy, AR display, work history, point cloud matching, etc.)

By utilizing LRTK, the latest smartphone RTK system, the following benefits can be obtained in pile-driving operations.

• High-precision guidance: The LRTK system achieves high-precision positioning within a few centimeters horizontally (within a few inches horizontally), and its guidance accuracy rivals that of conventional dedicated surveying instruments. By obtaining correction information from the Geospatial Information Authority of Japan's electronic reference point network and the CLAS signal of the Quasi-Zenith Satellite System Michibiki (QZSS) and performing real-time position correction, centimeter-level positioning (half-inch level positioning) can be stably achieved anywhere nationwide within communication coverage without a mobile base station (even in locations where communication is difficult, positioning can continue by receiving Michibiki's signals). On the smartphone app, a target display shows the direction and distance to a pre-registered target coordinate, and as you approach the target point a crosshair marker appears on the screen allowing fine adjustments of a few centimeters (a few inches). This enables pinpoint guidance to the stake-driving location, minimizing positioning errors.

• Work support via AR display: Using the camera's AR functions, you can overlay virtual piles and design models onto the real-world scene viewed through a smartphone. For example, in cases where it has been difficult to set survey points on steep slopes or in areas with poor footing, you can, from a safe location, place a virtual pile in the AR view to indicate "there is a pile here." In one slope reinforcement project, the AR pile-placement feature was used to place virtual piles from a distance to pinpoint positions, and then excavation was carried out directly beneath those points to drive the piles. This is a good example of how positions can be accurately determined even without placing physical markers, improving safety and reliability.

• Work History and Daily Report Output: In LRTK, the entire set of positioning and guidance data is recorded automatically. Photos taken on site are automatically tagged with precise position coordinates and orientation information, and each stake’s point data is saved to the cloud with timestamps. This leaves a record of "when, where, and what was done," making it possible to review the sequence later. Creating forms such as daily reports also becomes easier, and by exporting the data accumulated in the cloud you can quickly summarize the day’s work results (for example, which stakes were completed). Reporting omissions and input errors in survey results are reduced, making site management smarter.

• Use of point cloud data: LRTK not only handles stakeout but also supports 3D scanning (photogrammetry) functions using iPhone and iPad LiDAR and cameras. After pile-driving work, the same device can measure the as-built condition of the site as point cloud data, and that data can be instantly compared with the design model in the cloud. Because the acquired point clouds already have global coordinates, comparing them with design data and detecting deviations is smooth. For example, if you scan the construction area after pile driving is completed, you can confirm on the spot whether the actual placement of the piles matches the design, and you can also apply it to volume calculations. Since point clouds and drawing data can be centrally managed in the cloud, being able to seamlessly handle everything from pre-pile-driving stakeout to post-construction inspection and recordkeeping in one system is another major strength.

• Low cost and ease of use: Compared with high-precision GNSS equipment that traditionally cost several million yen, smartphone surveying devices like LRTK are offered at very affordable prices. Because they are inexpensive, provisioning one device per person becomes realistic, making them easy to adopt even for small and medium-sized enterprises and small-scale construction projects. Also, since they make use of existing smartphones, there is almost no need to become proficient with new dedicated terminals. The convenience of being able to perform positioning and guidance on a familiar smartphone screen should help accelerate their adoption on job sites.

Thus, by using LRTK, the efficiency and accuracy of pile-driving operations have begun to improve dramatically. There have been reports that stake layout that used to take half a day can be completed in about 1 hour with smartphone RTK guidance. In comparative experiments, stake layout using GNSS×AR was completed in about 1/6 of the time required by the conventional optical method, which took the most time, demonstrating astonishing efficiency gains. Moreover, even at disaster recovery sites where communications infrastructure has been cut off, a small smartphone RTK receiver can be deployed without bringing bulky equipment. In fact, there are cases in which, with base stations down, receivers continued to achieve high-precision positioning by receiving Japan's satellite positioning augmentation signal (CLAS), contributing to surveying at disaster sites. With small, inexpensive, and easily portable GNSS receivers, high-precision piling support is becoming possible regardless of location or circumstances.

Key Points and Outlook for In-house Implementation

When introducing new technology into your company's operations, it is advisable to keep the following points in mind while also looking ahead to future prospects.

• Limitations of GNSS positioning: Satellite positioning cannot achieve high accuracy unless there is a clear view of the sky. Under overpasses, inside tunnels, or in locations surrounded by tall buildings, positioning becomes unstable even with RTK (the so‑called "satellites are not visible" condition). In forests, reflections and blocking of satellite signals can also cause degraded accuracy or make positioning impossible. Therefore, in such environments it is important to prepare backup measures, such as combining with traditional optical surveying (total station) or establishing control points in advance.

• Handling the equipment: Even though they are smartphones and small GNSS receivers, they remain precision instruments. They have waterproof and dustproof features, but compared with surveying equipment that has dedicated rugged housings, the risk of damage on site is higher. When operating in rain or using them at heights or on heavy machinery, take measures to protect the devices, such as attaching fall-prevention straps or using waterproof cases. Also, because they are battery-powered, securing backup power is essential for long periods of continuous use.

• Personnel Adaptation: You should also be mindful of resistance to digital technologies. In particular, more experienced workers may feel uneasy about operating smartphone apps. When introducing them, it is important to provide thorough explanations and a training period to support skill acquisition. However, the operation itself is intuitive and the interface supports Japanese, so in most cases people appreciate the convenience once they try it. Demonstrating it on site so they can experience the benefits firsthand is recommended.

By establishing operational rules while keeping the above points in mind, you should be able to introduce GNSS receiver technology smoothly. Looking ahead, construction guidance that combines RTK positioning with smartphones could become an industry standard. At infrastructure construction sites where accuracy and efficiency are required, this technology will strongly support the commonplace yet difficult task of driving piles accurately and quickly. In the construction industry, which faces labor shortages and challenges in skill transfer, it is expected to contribute to creating an environment in which anyone can carry out high-quality construction work without mistakes.

Finally: Encouraging Simple Surveying with LRTK

In this article, we have introduced in detail the challenges in pile-driving work and the latest solutions using GNSS receivers from the perspectives of improving accuracy, increasing efficiency, and reducing manpower. The issues of "accuracy", "time", and "manpower" that were problems with conventional methods are being greatly improved by a new approach combining smartphone surveying and RTK. An era is imminent in which, without relying on specialized surveying teams, each worker on site can handle high-precision positional information and simultaneously achieve improved pile-driving accuracy and increased productivity.

Of course, there are constraints unique to satellite positioning and operational considerations for equipment management, but overall, construction guidance combining RTK and smartphones is likely to become the new standard on future construction sites. In infrastructure projects that demand accuracy and efficiency, this technology should strongly support the obvious-yet-difficult task of 'driving piles accurately and quickly'. Let’s make good use of cutting-edge RTK guidance technology and promote the creation of construction sites where anyone can perform high-quality work without mistakes.

The LRTK series is a solution that enables such simplified surveying. Using familiar tools—a compact RTK receiver and a smartphone—it enables centimeter-level positioning and dramatically shortens the time required for surveying and stakeout. It also supports i-Construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism, making it an ideal choice for the construction industry's DX (digital transformation). Please consider adopting LRTK, which advances job sites to the next stage through improved accuracy and efficiency. Make use of GNSS receiver-assisted stakeout support to update your construction sites to be smarter and more accurate.