STRABAG AG is a leader in infrastructure construction in Germany and is known to be one of the biggest construction firms in Europe. In recent years, the company has moved away from using conventional technologies to embrace digital construction technologies, and this has given it a reputation for delivering complicated high-speed roadway, railway and airport projects on time and within budget. The use of mobile mapping solutions and drones, in particular, has enabled STRABAG AG to redefine the delivery of its transport infrastructure projects. Some of the digital technologies adopted by the company include Building Information Modelling (BIM), LiDAR, drones, and advanced mapping solutions, which help the company deliver precise measurements of the construction site quickly. Drones and mobile mapping solutions also help the contractors and surveyors capture topographic data points or Ground Control Points (GCPs) safely, so that stakeholders do not have to manually visit the construction sites that are often inaccessible and dangerous, located in harsh terrains.
The Project: The Northern Bavaria Motorway Directorate (NBMD) tasked STRABAG AG to conduct a pilot study for the renovation of the Federation Motorway 93 or the Autobahn 93 (A93) in Bavaria. The length of the motorway is 276 km and it consists of two tracks – a short track from the A8 near the Austrian Border to A12 in Tyrol, Austria, and another from A72 in the north of Bavaria to Holledau A9. NBMD launched the pilot project by tasking STRABAG AG to scan and collect imagery of a section of the two-lane A93 highway and subsequently create a 3D model of the same.
The Technical Process: Surveying the A93 highway was challenging for STRABAG’s surveyors and crew because the highway has no speed limit, thus making it quite unnerving to capture ground measurements when cars race past at the speed of 150 km/hour. In order to capture precise spatial data and at the same time ensure the crew’s safety, STRABAG AG proposed using unmanned aerial systems (UAS) and other advanced surveying solutions to precisely capture data and deliver the project within budget and on time.
As part of its effort to start using more digital technologies and advanced surveying tools, STRABAG AG purchased Trimble’s MX9 Mobile Mapping Solution in 2018 and used it in the pilot study of the renovation of the A93 highway. The MX9 Mobile Mapping Solution is a field-to-field system by Trimble that combines high-density laser scanning, a spherical camera for panoramic and multiangle imagery, and a high-precision Applanix GNSS inertial measurement system. The Solution includes two laser scanners that have the ability to capture one million-point clouds per second of the scanning site, giving an incredibly high-density point cloud to form a 3D model.
To capture the point clouds of the A93 highway, the MX9 Mobile Mapping Solution was mounted on top of a special vehicle to scan all the visible structural features, including overhead details such as break lines, pavement edge lines, road and building signs, and all road markings. This enabled STRABAG AG to capture panoramic and multiangle photos of the entire 20 km section accurately, within the timeframe of just two hours. With two laser scanners on the MX9 Mobile Mapping Solution, STRABAG AG was able to scan ‘cross-wise’ and capture features that were otherwise blocked. So even if the view of one scanner was blocked due to the on-coming traffic, the other scanner most definitively captured the ‘blocked view’.
Along with Trimble’s MX9 Mobile Mapping Solution, STRABAG AG also used drones and the Trimble SX10 Scanning Total Station equipped with GNSS, to provide an exact location of the existing road structure and a map of the construction environment. Using the laser scanning device, STRABAG AG was able to survey and map at least 120 ground control points (GCPs), validating the data accuracy of the mobile mapping solution.
The point cloud data collected from the MX9 Mobile Mapping Solution, the Trimble SX10 Scanning Total Station, and the drones, was integrated and processed using the Trimble Business Center (TBC) software. The processed data was used to produce the Digital Terrain Model (DTM) of the A93 highway with a 1.5 cm horizontal and 2 cm vertical absolute accuracy – the required data specification. The 3D model and the DTM showcased a real-world view of the highway ─ from the smallest concrete joint feature to the pavement edge lines. STRABAG collected and submitted the point cloud dataset, the UAS imagery, and the DTM models to NBMD.
The process of surveying roads and highways with traditional tools is normally a time consuming and costly affair involving several days of work. However, by using Trimble’s MX9 Mobile Mapping Solution, STRABAG AG could collect the required field data within just a couple of hours and have it processed instantaneously to create 3D Digital Terrain Models of the construction environment. Stakeholders from STRABAG found that using the 3D mobile mapping technology allowed crews to work during traffic hours and helped them acquire centimeter-grade spatial data of high precision and accuracy. Using the 3D model generated, NBMD could integrate the spatial data with CAD and BIM, highlighting where and when an extension or an overpass was going to be built. The 3D spatial imaging technology also helped the Directorate expedite project delivery of complicated projects on time and within budget.
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