Essential for ICT construction! RTK piling balances accuracy and efficiency

Table of Contents

• Importance of ICT construction and RTK piling

• Challenges of conventional pile driving work

• What is RTK piling?

• Benefits of RTK piling

• Utilization of simple surveying with LRTK

• FAQ

Importance of ICT construction and RTK piling

In recent years, the construction industry has been promoting "ICT construction" (i-Construction) to improve productivity and ensure quality. Early ICT construction efforts focused on introducing automatic control of heavy machinery (3D machine control) in earthworks (such as land development and grading), but recently the application of digital technologies has expanded to structural works such as foundation piling for bridges. The Ministry of Land, Infrastructure, Transport and Tourism has also been developing guidelines for ICT-utilized construction, for example by drafting procedures for as-built management using three-dimensional survey data. ICT construction refers to initiatives that utilize digital technologies from surveying and design through construction and inspection to streamline and sophisticate construction processes. Among these, accuracy control in pile driving work is particularly important. If the positions of piles that form the foundations of buildings or bridges are off, it can significantly affect safety and structural performance. Therefore, driving piles into exact positions (pile centering) is the most important task in construction management; at the same time, shortening schedules and reducing labor are major site demands. As a key to reconciling the often conflicting goals of "accuracy" and "efficiency," pile driving methods that utilize RTK are attracting attention. This article explains what RTK-guided piling is and how it can achieve both accuracy and efficiency.

Challenges of conventional pile driving work

First, let us organize the challenges that conventional pile driving work faced. In conventional methods, survey teams used tapes and total stations on site to stake out positions for piles based on the coordinates shown on design drawings. It was common practice to measure distances from reference points and install markers on the ground called pile markers or batter boards, which machine operators then relied on to drive the piles. However, this manual staking process was time-consuming and labor-intensive and was easily affected by weather and terrain conditions. For example, surveying may be interrupted on rainy or snowy days, and it can be difficult to install accurate pile markers in highly uneven terrain. Also, because humans perform the work, survey errors and marking mistakes cannot be completely eliminated, and small offsets can lead to later construction errors. If pile position errors are discovered after construction, repairs and rework will incur extra time and cost and can affect the overall schedule.

Safety issues cannot be overlooked either. Marking out pile positions is done within the operating area of heavy machinery, so workers are always at risk of inadvertently approaching the equipment. The risk of survey staff falling or coming into contact with machinery increases particularly on slopes or muddy, unstable footing. In some cases, it was difficult to install pile markers on inclined sites, causing operations to stall. To solve these problems of conventional methods and to perform pile driving more accurately, efficiently, and safely, new technologies have attracted attention in recent years.

What is RTK piling?

A new piling method that has emerged to solve these issues is pile driving that utilizes RTK. RTK stands for *Real Time Kinematic*, and it is a positioning technology that adds correction data to positioning information from satellites such as GPS, reducing errors to a few centimeters. While conventional GPS can have errors of several meters, RTK enables centimeter-level high-precision positioning (cm level accuracy (half-inch accuracy)) even on construction sites. Specifically, a base station (a receiver that serves as a reference point) installed on site communicates correction information in real time with a rover (a receiver mounted on machinery or surveying instruments), dramatically improving positioning accuracy. Recently, enhancement signals from Japan’s Quasi-Zenith Satellite System (QZSS, "Michibiki") such as CLAS have been put into place. In addition, the spread of network-type RTK services (VRS method), which distribute correction information from electronic reference stations via mobile communication networks, has made centimeter-level positioning possible without installing a dedicated base station. With these infrastructure improvements, RTK technology is becoming more accessible than before.

So how is RTK applied to pile driving? The answer is that it provides real-time, high-precision position information to machine operators and survey personnel. By mounting an RTK-GNSS receiver on a pile driver (piledriver) or connecting it to a worker’s tablet or smartphone, the exact position where the pile should be driven can be determined on the spot. Traditionally, pile markers had to be driven into the ground before piling to indicate positions, but with RTK piling, a digital "car navigation" system informs the machine or person of the deviation between the current position and the target position.

For example, a tablet screen can overlay pile position data from the design drawing onto a map or AR (augmented reality) display; a worker who moves according to those instructions can accurately place a pile without being an expert. As the worker approaches the target position, guidance such as "○ cm remaining" is displayed, and when the specified position is reached, a marker overlaps on the screen to visually indicate completion of positioning. It is a site-version navigation guidance system: the combination of RTK’s centimeter-level accuracy (cm level accuracy (half-inch accuracy)) and digital technology has dramatically advanced piling work. Such a system that provides operators with real-time position information based on GNSS and three-dimensional design data is generally called 3D machine guidance and is a core technology of ICT construction.

Benefits of RTK piling

Pile driving that utilizes RTK simultaneously solves the accuracy, efficiency, and safety challenges associated with conventional methods. The specific benefits are as follows.

• Accuracy improvement: Because pile positions can be guided with centimeter-level accuracy (cm level accuracy (half-inch accuracy)), position offsets are almost eliminated. Construction can be carried out exactly according to design drawings, preventing construction errors and rework caused by position deviations. It is especially effective for projects requiring strict accuracy control, such as high-rise buildings and bridges.

• Increased work efficiency: The time required for surveying and marking is drastically reduced. On sites where surveying and marking used to take half a day, RTK guidance can reduce that to a few hours, greatly improving efficiency. In fact, there are reports that switching from conventional optical surveying to RTK + AR guidance shortened pile staking time to about 1/6. Of course, the extent of the effect depends on site conditions, but reducing machine idle time while waiting for surveying or staking leads to overall productivity gains.

• Reduced personnel and costs: The number of dedicated staff such as surveyors and assistants can be reduced, lowering labor costs. Because RTK systems can be used without specialized surveying skills, they are easier to introduce in sites facing labor shortages. Also, since retrofittable GNSS receivers and tablet apps can be used without special modifications to machinery, initial investment can be kept relatively low.

• Improved safety: It eliminates the need to perform risky on-site surveying in hazardous locations. For example, on slopes, AR can remotely identify pile positions from a safe location, reducing the need for workers to enter unstable areas. It also helps prevent near-miss accidents between people and machines around heavy equipment, improving overall site safety.

• Streamlined quality control: RTK piling leaves digital records of the exact coordinates of each installed pile. You can provide evidence that construction was completed within a few centimeters of the design position, making as-built reporting to clients and regulatory authorities smoother. Combined with photogrammetry data, it provides useful information for as-built management and later inspection and maintenance.

• Versatility: Once RTK-GNSS surveying equipment is introduced, it can be used for a wide range of purposes beyond piling. For example, it can be used for as-built surveys of ground shape after construction, locating buried utilities, and checking finishes by overlaying design drawings with on-site images in AR, making it a multipurpose DX tool on site.

Thus, RTK piling technology is a solution that realizes the ideal of "accurate, fast, and safe" on site. Because it simultaneously addresses traditional challenges such as ensuring positioning accuracy, shortening work time, coping with labor shortages, and improving safety, it is becoming an indispensable technology for ICT construction.

Utilization of simple surveying with LRTK

By adopting RTK piling on site, high-precision and efficient piling can be performed without relying on a specialized surveying team. Furthermore, in recent years, a simple surveying method using smartphones has emerged as an easy-to-introduce approach even without expensive dedicated ICT machinery. A representative example is a system called LRTK developed by a startup originating from Tokyo Institute of Technology. With LRTK, a dedicated ultra-compact RTK-GNSS receiver is attached to a smartphone or tablet, and design data and current position are displayed in AR on a dedicated app, enabling anyone to easily perform pile staking and surveying. Simply attaching a receiver weighing only in the 100-gram range to the back of the smartphone transforms it into a centimeter-class surveying instrument without complicated cable wiring. Intuitive screen operations visualize the points where "the pile should be driven," so even non-veterans can work without hesitation. Because of the convenience of a smartphone-based system, one-device-per-person operation is realistic, and it has already begun to be adopted at many sites.

Using simple surveying with LRTK, pile guidance and as-built measurement—previously reliant on specialized equipment and skilled technicians—can become routine tasks that anyone on site can perform. The burden of strenuous surveying work is reduced, allowing freed-up time to be allocated to other productive tasks. As a tool that advances on-site DX (digital transformation) one step further, LRTK supports construction from both accuracy and efficiency perspectives. The use of such advanced technologies also contributes to alleviating labor shortages and improving work styles. With fewer repetitive surveying tasks, site staff can spend more time on higher value-added work. If you are interested, consider actively adopting these new technologies to experience next-generation construction styles.

FAQ

Q1. What is the difference between conventional pile driving methods and RTK piling? A1. In conventional methods, survey staff manually mark pile positions on site, and heavy machinery drives piles based on those marks. With RTK piling, GNSS positioning allows machines and workers to understand in real time the difference between their current position and the design pile position. In short, digital technology provides navigation instead of manual pile markers. As a result, surveying work is reduced and accuracy is dramatically improved.

Q2. What level of accuracy can be achieved with RTK piling? A2. With general RTK-GNSS positioning, planar positional accuracy is typically within an error range of 2-3 cm (0.8-1.2 in) (and under favorable conditions, centimeter-level accuracy (in the 1 cm range (around 0.4 in)) is possible). Vertical accuracy is also on the order of a few centimeters. This level of accuracy is sufficient for usual civil engineering work and can achieve results comparable to conventional total station surveying. However, accuracy is affected by satellite reception and the surrounding environment, so equipment calibration and checking the positioning environment are important.

Q3. How much does work efficiency improve by introducing RTK piling? A3. It depends on site conditions, but the time required for surveying and marking can be greatly reduced. For example, at one site, work that used to take half a day for surveying and marking pile positions was completed in just a few hours with RTK and AR guidance—an efficiency improvement of more than five times. Because the same work can be done with fewer personnel, it directly leads to shorter overall schedules and labor savings. Of course, the extent of the effect depends on site conditions, but reducing heavy equipment idle time while waiting for surveying or staking contributes to overall productivity gains.

Q4. What equipment and preparations are required to introduce RTK piling? A4. Fundamentally, you need a GNSS receiver capable of centimeter-level positioning and software that uses positioning data (apps or systems installed on machinery). GNSS receivers can be provided as a set of a fixed base station and a rover, or you can use a network-type (virtual reference station) RTK service via mobile networks. In addition, a tablet or monitor that shows pile positions based on the receiver’s data is required. Recently, aftermarket kits that can be retrofitted to machinery and RTK devices that attach to smartphones (e.g., LRTK) have appeared, making it easier to introduce systems depending on budget and site scale.

Q5. What if satellite positioning cannot be used due to location or weather? A5. In places where sky visibility is limited—such as among high-rise buildings, in mountainous areas, or inside tunnels—GNSS positioning is difficult. In such cases it is common to combine other positioning methods, such as optical surveying with total stations (TS) or laser guidance systems. RTK functions in light rain, but during typhoons or thunderstorms, it is advisable to suspend surveying work for safety reasons. By using RTK and conventional technologies appropriately according to site conditions, stable construction accuracy can be maintained.

Q6. Can non-experts operate RTK piling systems? A6. Yes. RTK piling systems feature intuitive operation screens and guidance functions so that non-experts can use them. In practice, beginners can identify pile positions simply by following arrows or AR markers displayed on a smartphone or tablet. Once basic equipment use is learned, accurate pile staking can be performed without specialized surveying knowledge. Indeed, ease of use is a major advantage of adopting RTK technology.

Q7. Is RTK piling necessary for small-scale projects? A7. It is not always indispensable, but the benefits of RTK piling can be realized even on small projects. Tasks that were previously done by simple visual estimation can, with RTK, lead to fewer re-measurements and rework, improving efficiency. However, for very small sites that require only a few piles, some may forgo introduction from a cost-effectiveness perspective. With the decreasing cost of RTK equipment and advances in smartphone-based solutions, it is expected that RTK piling will become standard even for small- and medium-scale projects in the future. In public works, the adoption of RTK-GNSS for ICT construction is spreading regardless of project size, so small projects may also commonly use it going forward.

Q8. How does RTK piling differ from surveying with a total station? A8. Total station (TS) surveying can achieve millimeter-level accuracy, but it requires setting up the instrument and often multiple personnel, making it labor-intensive for wide-area construction. RTK piling has the advantage of allowing one person to efficiently position over a wide site and proceed with work while confirming positions in real time. However, in places where GNSS reception is not possible (such as inside tunnels or indoors) or when extremely strict accuracy is required, TS assistance is effective. By using RTK and TS according to site conditions, you can leverage the strengths of each method for accurate control.

Q9. Can a smartphone’s GPS be used instead? A9. General smartphone GPS has errors of several meters, making it difficult to use for high-precision tasks like pile driving. RTK uses dedicated correction information to reduce errors to the centimeter level. Recently, solutions such as external RTK receivers that attach to smartphones (e.g., LRTK) have appeared, enabling centimeter-class positioning with familiar devices; however, standalone smartphone GPS alone is insufficient for the required accuracy.

Q10. Does RTK positioning take a long time to prepare or initialize? A10. Even when installing a dedicated base station, equipment setup is completed in a few minutes. With modern systems, RTK positioning often achieves initialization (fixed solution acquisition) within one minute, so you are not kept waiting long to start work. Satellite geometry and weather can sometimes lengthen initialization time, but even so, high-precision positioning can generally begin much more quickly than conventional batter board installation and surveying.