Investigating a Collapsed Tunnel After a Landslide in the Swiss Alps
A road tunnel in the Swiss Alps was struck by a landslide, cutting off access to a village and disrupting a popular ski resort. The Elios 3 drone played a crucial role in assessing the damage and planning an effective response. This case highlights how advanced technology can make emergency situations safer and more efficient.
Key Benefits in a Nutshell
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Safety The unstable condition of the tunnel made it too dangerous for human entry. Instead, local authorities used the Elios 3 to gather critical data without risking lives. |
Efficiency The Elios 3 was deployed quickly, capturing both LiDAR and visual data simultaneously, which allowed for rapid analysis and decision-making. |
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Analysis The LiDAR scans provided detailed point cloud data, allowing authorities to visualize the entire tunnel structure, including where the landslide had entered and its path. |
Speed The quick deployment of the drone enabled early repair efforts, and the tunnel was reopened by June of the same year, minimizing disruption during the busy summer season. |
Landslides are common worldwide and can be triggered by natural factors like mountain slope geometry, or human activities such as deforestation and construction. Climate change is also increasing their frequency and severity. In Switzerland, landslides often occur in early spring due to changing weather conditions that loosen soil and rock, leading to sudden collapses.
A Landslide in the Swiss Alps
On the night of February 3rd, 2024, several landslides hit the valley around Riddes, Switzerland. One road tunnel between Riddes and La Tzoumaz partially collapsed, severely limiting access between villages and cutting off parts of a major ski resort. Every day the tunnel remained closed added to the challenges faced by residents and tourists, who had to take long detours. Determining the closure duration was essential to keep affected people informed.
The interior of the tunnel was covered in debris. Image credit: Canton ValaisÂ
Access to the tunnel was extremely dangerous, so investigators needed a safe and fast way to gather information. Local authorities turned to innovative solutions to get answers quickly.
Planning a Landslide Investigation with Drones
The landslide occurred in the canton of Valais. Authorities needed to understand the cause of the collapse and assess the tunnel's damage to plan repairs and prevent future incidents. Due to the site’s instability, entering the tunnel was not an option, so a remote survey was necessary. The Valais authorities used the Elios 3 drone equipped with a Surveying Payload to capture images, videos, and LiDAR data, providing a complete view of the situation inside the tunnel.
This project was handled by the Department de la Mobilité du Territoire et de l’Envrionment, the local infrastructure authority. Since the tunnel is owned by the canton, no external parties were involved in the investigation phase.
Flying a Drone in a Collapsed Tunnel
The tunnel, built decades ago, may have contributed to the collapse. A small window in the outer wall, likely added for natural light, may have weakened the structure over time. Within 24 hours of the incident, the Valais drone pilot began planning the mission, focusing on the area around the window.
The visual feed from the Elios 3 showed how the landslide caused the tunnel roof to collapse
The initial flights focused on mapping the debris, assessing damage, and gathering situational data to help clear the area. LiDAR surveys were key to understanding the layout of the collapsed section. Subsequent flights examined the window’s impact on the tunnel’s stability, collecting detailed images for further analysis.
Findings from Drone Surveys in the Collapsed Tunnel
The Elios 3’s images revealed that the tunnel had been deteriorating over time. The open window allowed cold air to enter, accelerating freeze-thaw weathering that weakened the rock. Over 60 years, this process, combined with traffic vibrations and minor seismic activity, gradually compromised the tunnel’s structural integrity.
Investigators also believe that explosives used during the original excavation may have caused decompression in the surrounding rock, weakening the outer walls. By 2023, signs of instability were evident, with small rockfalls occurring in December, reducing the thickness of the rock pillar separating the tunnel from the surface.
LiDAR scan clearly shows the layout of the collapsed tunnel section and where the rocks came through
These findings will inform future repairs and help improve landslide prediction and mitigation strategies. As climate change increases the likelihood of such events, using drones like the Elios 3 ensures that investigations can be conducted safely and efficiently.
The Impact of Drones in Emergency Response
Without the Elios 3, investigating the collapsed tunnel would have been extremely difficult and risky. Sending personnel into the tunnel was not an option, and securing the area could have delayed recovery efforts significantly. The use of drones allowed for a faster, safer, and more efficient assessment, enabling the authorities to respond quickly and effectively.
The fly-through of the LiDAR scan shows the full extent of the damage
The use of the Elios 3 in this case was transformative. It allowed investigators to enter the tunnel just one day after the incident, vastly improving the speed of the response. In the past, securing a landslide site could take days or even months before any meaningful data could be collected. With drones, teams could work more efficiently and with fewer people, saving valuable time and resources.
By leveraging innovative technology that prioritizes safety, the Valais authorities were able to gather critical data quickly while ensuring the well-being of all involved. The insights gained from this event will play a key role in future repairs and research, especially as climate change continues to increase the risk of unpredictable geological events.
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