Reference, completed project

Monitoring and support services for the City of Paris concerning the project to ensure the safety of the Parc des Buttes Chaumont

The Parc des Buttes Chaumont (Les Buttes Chaumont Park), situated in Paris' 19th district, is a complex site with a long history. This landscaped park includes an artificial island, caves and a view over the city from a hill that was previously exploited for its gypsum. After the occurrence of rock falls and subsidence in 2021, the City of Paris asked BRGM to carry out an in-depth assessment of the site and help the City define and implement a project to make the park safe.

13 November 2024

East face of the island (Parc des Buttes Chaumont, Paris, 2023).

The need

The Parc des Buttes Chaumont was used as a gypsum quarry from the 16^th to the 19^th centuries, before being converted into a landscaped park by the architect Adolphe Alphand between 1863 and 1867. The site was laid out in keeping with the Romantic spirit of the time, and visitors can today stroll around the Park's various features, including an artificial island and caves, and enjoy a view of the city of Paris from a mound made from a large pile of gypsum that was left on site. In May 2021, following the occurrence of various problems (falling rocks, subsidence, etc.), the City of Paris' Park and Green-Space Department asked BRGM to conduct an initial assessment of the state of the park. BRGM was then commissioned to carry out a series of specific missions: site survey, geological and geotechnical diagnosis, definition of an instrumentation programme, geophysical data acquisitions and support services as part of the project aimed at restoring the park and ensuring its safety.

The results

Initially, documentary research was carried out concerning the history of the Park. This involved three phases: information gathering, classification and sorting of the data, and finally an overall analysis and summary of the information. Around 2,800 documents were collected, classified, digitised and processed. The most important information was entered in a GIS database, then summary sheets were drawn up for each zone.

The second phase involved analysing the likelihood of rock falls, which resulted in the roll-out of an instrumentation (sensor) programme for the most high-risk sectors and the demarcation of various zones that needed to be closed to the public.

Since the beginning of 2023, regular monitoring of the instrumentation systems installed on site and quarterly visits to the Park have been carried out by BRGM. Finally, following the draining and cleaning of the Park's lake in late 2023/early 2024, a geophysical data-acquisition campaign (micro-gravimetry and radar) was carried out from the bed of the lake, with the aim of identifying subsurface anomalies linked to former open-pit and underground mining operations.

Our partnership with BRGM is important because it gives us an expert insight into the underlying problems of this iconic Parisian park. The study enabled us to assess the risks present in certain areas, which we then used to back up our request to close the park to the public while we carried out the necessary work. BRGM's support was also invaluable during the work phase, since they helped us choose a service provider capable of meeting our safety requirements and the constraints linked to a listed park, while safeguarding the picturesque nature of the site and its biodiversity.

Ghislaine Lépine, Head of the Studies and Works Division, City of Paris

Monitoring of the gypsum rock faces (Parc des Buttes Chaumont, Paris, 2023).

Using the results

The work carried out enabled us to retrace the geological and geotechnical history of the Park, while also gathering additional data, which was exploited to monitor the most sensitive areas and ensure public safety. BRGM's mission will continue until all the restoration and safety work in the Park has been carried out, with the work scheduled from 2025-2026.