Quarries and subsoil of Paris’s 6th arrondissement
High risk Paris 75006
The 6th arrondissement (Odéon, Saint-Germain-des-Prés, Val-de-Grâce) lies on the Grand Réseau Sud. The Lutetian coarse limestone quarries there were worked at one or two levels. The density of Haussmannian buildings above these underground voids makes it an area to monitor: subsidence, cracking and sinkholes (fontis) are real risks there. The area’s geotechnical conditions require G1 soil studies before any underpinning project.
What public data say about the 6th
| Underground network | Grand Réseau Sud (GRS) |
|---|---|
| Mined rock | Lutetian coarse limestone |
| Undermined area | Part of the ~508 ha of the Grand Réseau Sud. |
| Galleries | Included in the GRS’s ~200 km of galleries. |
| Selected risk level | High |
| Confidence in the classification | high |
| Nature of the ground | Lutetian limestone plateau |
| Foundation issue | Ground generally stable at depth outside areas with listed quarries. A G1/G2 geotechnical study is recommended before any underpinning or construction project. |
Sensitive sectors of the 6th
- Odéon, Saint-Germain-des-Prés, Val-de-Grâce areas
- Dense Haussmann buildings above underground voids
Ground, fill and clay shrink-swell
The 6th arrondissement (Odéon, Saint-Germain-des-Prés, Val-de-Grâce) lies on the same Lutetian coarse limestone plateau as the 5th, mined by the Grand Réseau Sud (see quarry section).
Ground generally stable at depth outside areas with listed quarries. A G1/G2 geotechnical study is recommended before any underpinning or construction project.
Unlike almost all French municipalities, inner Paris has no official mapping of the clay shrink-swell hazard (RGA). The BRGM explains this explicitly: the Paris subsoil is largely made up of reworked and artificial materials (backfill, infilled former quarries), which does not correspond to the standard methodology for this mapping — centred on detached houses, which are in the minority in Paris. This does not mean that there is no risk of differential settlement, but that no official area-by-area study exists for the capital: a ground investigation remains the only reliable way to assess a specific plot before purchase or construction.
Your steps in the 6th before a purchase or works
A G1 ground investigation is recommended before any underpinning project, major renovation or purchase. IGC (Paris quarry inspectorate) consultation and an Errial statutory risk statement (ERP) are compulsory.
- IGC (Paris quarry inspectorate) information sheet — the authoritative source on the condition of the parcel’s subsoil: €10, issued within 8 days, via the City of Paris online service.
- Statutory risk statement (ERP) — mandatory for sale and letting, generated from Errial; note, it does not return cavity data in Paris.
- geotechnical survey — G1 mission before purchasing a building plot, G2 AVP before a construction or underpinning project.
- Referral to the IGC (Paris quarry inspectorate) for planning — prefectoral orders require it to be consulted for any planning permission in a quarry-risk area.
Frequently asked questions
Are there underground quarries beneath Paris’s 6th arrondissement?
Yes. The 6th arrondissement is recorded in the public data of the IGC (Paris quarry inspectorate) as an area affected by the « Grand Réseau Sud (GRS) » network, in Lutetian coarse limestone. The assigned risk level is « High », with high confidence in the area’s classification. The Val-de-Grâce / Odéon area is included in the Grand Réseau Sud on the Left Bank.
How can I tell whether my precise address in the 6th is in an undermined area?
Quarry zoning must be read at plot level rather than arrondissement level. There are two options: the official information sheet from the IGC (Paris quarry inspectorate), at €10 and issued within 8 days, which is the legally binding source; and Sous-sol Paris’s instant pre-assessment, at €15, which matches your address against public data and immediately provides you with a readable report, including the steps to take. This pre-assessment is for information only and does not replace the IGC information sheet, the statutory risk statement (ERP), or a geotechnical study.
Why does the 6th’s cavity data not appear on Géorisques?
Because for départements 75, 78, 91, 92, 93, 94 and 95, cavity data are not published on the Géorisques portal: they can be consulted with the IGC (Paris quarry inspectorate) for Paris and the inner suburbs, or with the relevant interdepartmental service. This is why a standard statutory risk statement (ERP) remains silent on Paris quarries and gypsum.
Is the 6th’s quarry risk covered by insurance?
Disorders linked to former quarries do not fall under the « natural disaster » scheme. In the event of collapse, infill works, estimated at 40 000 to 200 000 €, remain the responsibility of the owners. This is what makes checking before purchase essential.
Other arrondissements
- Subsurface of the 5th arrondissement
- Subsoil of the 7th arrondissement
- Subsoil of the 4th arrondissement
- Subsoil of the 8th arrondissement
- Subsoil of the 12th arrondissement
- Subsurface of the 13th arrondissement
- Subsoil of the 14th arrondissement
- See the 20 arrondissements
Sources
- City of Paris — Everything you need to know about the subsurfaces
- Institut Paris Région — Underground risk study (quarries)
- Wikipedia — Paris, Geology section
- BRGM InfoTerre — Explanatory note for the 1/50000 geological map of Paris
- BRGM — Why is there no map of the clay shrink-swell hazard for Paris?
- Géorisques — Clay shrink-swell, 2026 version (data)
- Géorisques — Underground cavities (data)
- City of Paris — the IGC (Paris quarry inspectorate) location
- City of Paris — Known areas of former quarries (IGC)
Page updated on 11 September 2026.