Digital monitoring of major urban construction sites

• 300,000 inhabitants
• 160,000 vehicles in the main part of the city
• 190 million tram passengers every year.

Not only does the highway A5 influence the planning scenarios in the greater Karlsruhe area, but also the inner-city use of the state street B10. This is the most important inner-city east-west connection for the region. The city of Karlsruhe as well as the federal state of Baden-Wuerttemberg react on the development of the traffic and the whole region by launching two exceptional tunnelling projects for the relief of over-ground traffic with the project The Combined Solution.

Projects like this come with concerns from citizens. Construction noise, disruption of daily life, costs, pollution and environmental restrictions are only a part of the potential issues that must be taken into account when working on this kind of large-scale urban projects.

The city government and the Karlsruhe Rail Infrastructure Society (KASIG) builders have set up a long-term and very early information campaign for this purpose. This takes place in the form of a project website, but also through public events and an information centre. The aim of the builders as well as of the participating construction companies and consortia was also to make the best use of the possibilities of digital solutions for construction site documentation. Leica Geosystems’ solutions for surveying used by Karlsruhe Ingenieurbüro GEO GmbH are the decisive factors in this digital documentation.

Highest accuracy from day one

The construction companies Ed. Züblin and Schleith are responsible for the construction of the Kriegsstraßentunnel next to Karlruhe’s major area, Ettlinger Tor. Combined with a second tunnel in Kaiserstraße, both construction projects make up The Combined Solution for the city of Karlsruhe, which will help to significantly alter the traffic situation in the inner city from 2020 and 2021 respectively.

In the Kriegsstraße, this means that the vehicles are brought underground, while trams, pedestrians and all bicycles move above ground. On a path of 1,600 metres, the road tunnel dramatically changes the cityscape - as well as during the construction work. The construction planning and subsequent construction supervision is also given special importance for this reason.

The objective of the construction supervision cooperation, consisting of DB Engineering & Consulting, Emch+Berger and BUNG, is to obtain:

• highest accuracy in surveying
• preservation of evidence
• monitoring.

Before working on new construction sections, the task was the initial surveying of the construction area as well as an area of 50 m in all side streets. The expected accuracy of the data was 2 cm. This task was taken over by the team of IngenieurTeam GEO, using the Aibot X6 unmanned aerial vehicle (UAV). Equipped with the RTK and GNSS module, this technology allows airborne data to be collected parallel to the on-site operation, delivering highly accurate data by combining the Aibot HP GNSS 2 and the Sony Alpha 6000 with a 20 mm lens.

A special challenge when flying in the city centre

Around the project, the Federal Court of Justice and the Karlsruhe State Theatre are critical buildings. As is customary in the case of a tunnelling construction site, it must be ensured that the construction does not lead to unplanned changes in the environment. Any reductions or unwanted volume changes must be excluded. This exclusion has to be documented and monitored. Conventional methods can only be used to a limited extent in parallel to construction measures for security and time reasons.

The use of an UAV was then recognised as an optimal solution for data capturing in the sense of an efficiency-oriented project process. The advantages of the 3D measurement and the monitoring compared to a purely point-based data acquisition using terrestrial methods lie in particular in the various usage scenarios of the generated data. They can not only answer questions from a surveying engineer's point of view, but they can also be used as a basis for the planning of the traffic routes during construction work. They can be used in pro- and retrospective construction planning and are a decisive factor in volume calculation almost in real time.

On one hand, you have the advantages of using UAV; on the other, you have challenges of flying in the city centre. Thus, the narrowness of the city has to be taken into account already in the planning of the automated flight, and, therefore, the flight route and altitude planning has to be defined specifically. Potential disturbances of the flight by cranes, vegetation and possible magnetic field disturbances due to the existing infrastructure and development play a role.

Benjamin Busse, an experienced expert in the field of the use of surveying drones at IngenieurTeam GEO, has therefore placed special emphasis on the involvement of all stakeholders during the planning phase.

"The new drone regulations in Germany do not allow flights over federal streets," said Busse.

"Thanks to a good relationship with all stakeholders, we got the special permission for the inner-city flights over the B10 with traffic, pedestrians and tram."

Digital results and economic benefits

The deliverables for the project included:

• classical orthophotos
• high-resolution single images for documentation
• digital elevation models
• point clouds.

At the same time, the inspection of traffic route planning was mandated. This took place on the basis of existing plans, which were combined with the information from the orthophotos. As a result of the data from the flights and the high information quality, it is now planned to carry out quarterly monitoring, critical volume calculations as well as a supplement to the construction site diary through videos and photos from the bird's perspective with the help of UAV solutions.

Using conventional measurement and surveying methods, not only significantly less data could be collected, a team of five people would have needed six weeks to deliver the desired results. The team of two people for the UAV workflow only needed seven days.

Conventionally, Leica Geosystems total stations were used. The UAV team worked with a Aibot X6 Version 2, the Sony ILCE-6000, the Aibot HP GNSS 2 as well as a Leica Viva GS15 GNSS Smart Antenna for measuring the ground control points. The costs for the client using the conventional method would have been 180 per cent higher than working with the UAV solution. The monetary perspective is even more attractive from the UAV operator's point of view: the costs for IngenieurTeam GEO using the UAV solution were only a fifth of the costs of conventional methods.

"We see the UAV technology as part of our tool box," adds Martin Schwall, co-founder and managing director with IngenieurTeam GEO. "From a customer's point of view, UAVs allow fast and digital results with many advantages for additional information."

Digital workflows offer many advantages

The use of the UAV solution from Leica Geosystems offers a multitude of advantages. The digitisation of the processes associated with construction projects always depends on a high data quality and density. For example, the information from the UAV flights can be used not only for planning and monitoring but also for machine control and project communication tasks. In a further development step, the data of the UAV will also be seamlessly integrated into the software solutions of Leica Geosystems.

The results are not only faster, but can be customised to meet individual requirements with little effort. While conventional methods generate selective data, they do not capture image data, and, therefore, do not allow digital visualisation. The use of a digital end-to-end solution based on UAV, corresponding sensor technology (here high-resolution RGB camera) and suitable software for postprocessing and data processing offer real benefits, such as:

• 3D measurement information
• option of a parallel inspection based on the image data
• data capturing parallel to the day-to-day business
• much higher safety for the locally working surveying engineers and UAV operators.

The generated data is the basis for answering existing and future questions and will help to archive all construction progresses from the first day.

"As a next step, Leica Geosystems will fully integrate the UAV solutions in the software solutions for construction, monitoring and surveying," said Valentin Fuchs, product manager UAV, Geospatial Solutions Division, Leica Geosystems. "Helping our customers to visualise information and to use the collected UAV data to automate and speed-up processes is part of the bigger picture of future developments."