Monitoring of slopes, rock faces and masonry walls in a 19th century public park: the example of the Buttes Chaumont Park (Paris, France)

Developed on former gypsum quarries, the Buttes Chaumont Park is a 25-hectare geotechnical complex that is unique in the world. After three years of heavy work to create, in particular, an artificial cave, a lake and an island, the park opened in 1867 and has suffered gravitational hazards ever since (landslides, rockfalls and sinkholes). The BRGM has worked with the Paris City Council since 2021 to characterize the geological and geotechnical context, identify major gravitational hazards, and monitor the evolution of instabilities in slopes and rock/masonry walls. In this context, the BRGM has proposed, defined and followed a geotechnical supervision scheme including four levels of monitoring: detailed quarterly site visits since March 2023, bimonthly tacheometric surveys (operating since December 2022), monthly manual gauges measurements (since January 2024), and automatic extensometers and temperatures measurements (since March 2024). The interpretation of the data allows to confirm and/or complement the gravitational hazard mapping that had been carried out in 2022. By analyzing the correlation between displacement measurements and meteorological conditions, we could also differentiate between seasonal/daily trends mainly associated with temperature variations, and displacements associated with gravitational processes. These results help mitigate risks in the Buttes Chaumont Park in its current state, and adapt works planned in the coming years to restore and secure the park.