Advanced 3D technology for laying asphalt has been used in EUROVIA CS, a member of the VINCI Construction CS Group, for a number of years. It helped the Czech company for example during the construction of the highway from Hradec Králové to Jaromer, which was put into operation in the fall of 2021. On the construction of a new section of the D35 highway ‒ from Ostrov to Časy ‒ EUROVIA CS applied the Trimble Roadworks 3D Paving Control Platform technology, which was supplied by SITECH Czech.
Something is different here...
Ivan Cupal is the chief construction manager of EUROVIA CS and the main initiator of the use of the innovative 3D method. According to Ivan, the actual purchase of the technology was preceded by about two years of preparation and evaluation, during which exact calculations of the return on investment were made, and the productivity was estimated.
On the project, one can tell that there is a Trimble paving control system in use because of the two yellow masts on each side of the paver, which are connected by a cable to the control unit and subsequently to the control monitor at the rear of the machine. Since there are two masts (each controlling one side of the paver), this is a dual system. On the construction site, there are also several total stations at work, which are located on the edge of the newly laid road. They are also a sure sign that modern technologies are at work here...
Work on the D35 in full swing
During the visit, the bottom asphalt layer of the road is being laid over a relatively short distance (about 70 meters), connecting the two bridge sections (supplied by another associated company). Due to the section being short, a short screed (with a span of 6–7.5 m) was fitted to the paver. After laying the asphalt mixture in one lane, the machine returns to its starting point, it is set to the desired height and it paves another lane. Meanwhile, the new surface is compacted with asphalt rollers. The Trimble system is used when laying mechanically reinforced aggregates and underlying asphalt layers for precise leveling (6 + 6 cm VMT 22). A wide SB 250 paver (with a span of up to 12 m) is used for laying the base layers on continuous sections and subsequently for laying the bedding and abrasive layers. When laying the bed layer, the Trimble system is used in combination with a leveling frame to adjust the projected height of the highway. "The system from Trimble is suitable for very precise laying of asphalt, which requires the monitoring of the height. When we drive continuous long sections, we put the 3D system on a long screed and pave the whole length of one lane," explains Tomáš Kloz, foreman of EUROVIA CS.
Description of the technology
The basic building block of the system is a high-level digital model of the terrain. This is uploaded to the Trimble paving control system installed on the paver. The same model is uploaded to the Trimble field controller (a special measuring device with a screen, with which the worker behind the paver regularly checks the current height of the laid surface before compaction).
The paver can be equipped with a 3D leveling system, which checks the height on one side of the screed of the paver and on the other side calculates and sets the cross slope, which is automatically calculated from the direction of travel of the paver. The second variant of the leveling system uses height control on both the left and right side of the paver screed. This equipment set-up is ideal if the paver is working with a screed wider than six meters or is laying surfaces that are in curves and slopes.
The control unit is connected to two communication prisms, which are located on the masts on the trailing arms of the paver. These monitor the total stations and measure the position of the paver screed. All information is displayed on a ten-inch tablet with the Android operating system, through which the required height corrections and settings of the 3D leveling system are also carried out.
If working with a short screed without stopping, there are three total stations on the construction site (two are intended for guiding the paver; the third for independent control of the laid layer using a measuring stick with a field controller). If the paver works with a long bar without stopping, a total of five total stations are required (four for guidance, one for independent inspection).
For the sake of double checking, manual measurement is still taking place during the course of the project. A worker with a measuring rod moves on the rear platform and randomly measures the actual height of the laid surface. This is then compared with the height indicated by the system on the paver. According to Tomáš Kloz, there are only minimal manual adjustments to the laying height, usually only when connecting to a new lane. Otherwise, the Trimble 3D system essentially works fully automatically without the need for manual height corrections.
Advantages versus specifics of use
One of the necessary activities when working with a 3D system is calibrating the screed. After installing or replacing the smoothing bar, and before starting the actual work, it is necessary to aim the lower edge of the bar against the prism located on the mast of the trailing arm to determine the individual distances. Also, minor corrections have to be made every morning (the recalibration of the system). It is also necessary to calibrate and charge the total stations, and preparing the 3D digital elevation model of the terrain also takes some time.
As the representatives of EUROVIA CS confirm, the benefits clearly outweigh the investment. By controlling the paver using a 3D digital terrain model, the speed and efficiency of laying asphalt is rapidly increased. Fewer employees are needed on the construction site (it works in automatic mode), there is no need for a surveyor to be permanently present, and last but not least, there is no need to worry about the construction of string lines, which is a classic, conventional method of laying control, known for decades. "It takes up to four days to set string lines on more difficult sections, and we are then confined to only the staked space," says Tomáš Kloz, adding: "When you have a 3D system on your machine, you can cross over to any section of the highway, in short, you are much more flexible."
The second benefit that is mentioned often is accuracy. The Trimble Roadworks 3D system achieves millimeter accuracy; the exact number depends on the type of material being laid. In general, the finer the material to be laid, the higher the accuracy of the work. The variance stated by the manufacturer is 3-5 mm.
Other benefits derive from the technical configuration of the system. Trimble Roadworks 3D automatically adjusts both sides of the paver screed. In practice, this means that the system is able to monitor not only the height of the laid surface, but it can also take into account the current position of the paver, including, for example, rotation. "The software can calculate how the paver is turned in relation to the road, what the slopes should be, and the system automatically adjusts the level on the screed accordingly," explains Tomáš Kloz. The dual system allows the operator to efficiently lay the surface both on straight sections and in bends, on sections with an elevation and the like. In more fragmented terrain, however, it is necessary to count on deploying a larger number of total stations in order to ensure line of sight visibility to the paver-to-total-station axis. Another advantage can also be the ability to reset the system to single mode at any time, in which case one side of the machine is controlled by the total station and the other by the 3D tilt.
"The deployment of the Trimble 3D system from SITECH has a huge benefit for us in terms of speed of work, ease of use and accuracy," concludes Ivan Cupal. "It fully proved itself on the construction of the section of the D11 highway, which we completely finished using a 3D terrain model. Of course, there are places where this technology does not fit, but in ninety-five percent of cases we were able to deploy it without any problems," adds the chief construction manager of EUROVIA CS.
One of those examples where the functionality is limited, is if there is a large gradient on a short section and it would therefore be necessary to deploy a large number of total stations. During the pilot operation of this new technology in the Czech Republic, the EUROVIA CS team was able to rely on the comprehensive support of SITECH Czech, which helped with the debugging of systems, the supply of the necessary components and the training of employees.
For more complex projects, SITECH offers the possibility to rent extra total stations or other necessary components. More information can be found on the website of SITECH Czech.
Trimble Roadworks 3D enables, among other things:
- laying asphalt layers with an accuracy of 3-5 mm,
- minimizing the amount of asphalt used,
- reducing the amount of waste due to more accurate work,
- use of different types of material
How to program the machine from the office?
Thanks to the connection between the office and the field, it is possible to communicate more efficiently and the time required for data transmission is reduced. The Trimble SNM941 Connected Site Gateway data transfer modem enables the automatic wireless transfer of 3D models stored in the cloud, from the office to the machine. The machine operator always has the latest version of the project at his disposal. In addition, the productivity data obtained from the machine is automatically transferred back to the office, where they can follow the progress of the construction work online, download diagnostic files and rely on the technical support of SITECH Czech.