The S-PASS project and its challenges
The S-PASS project aims to collect and analyze subsurface data from the Greater Paris metropolitan area. Through a 3D digital model integrating geology, geotechnics, and infrastructure, it seeks to improve subsurface knowledge, share it with citizens and developers, and evaluate possibilities for sustainable use of this resource. Among the envisioned applications, geothermal energy and the valorization of construction materials are priority areas.
URBIDAS: unveiling urban subsurface through DAS imaging
The urban subsurface, often overlooked, plays a key role in the energy transition and sustainable development. The regional S-PASS project, in collaboration with the Université Gustave Eiffel, aims to better understand and leverage the subsurface resources of the Greater Paris metropolitan area. Within this framework, the exploratory URBIDAS project innovates by using seismic imaging techniques based on telecom optical fibers to characterize and monitor the near-surface urban subsurface.
URBIDAS: innovation for urban subsurface monitoring
The URBIDAS project (URBan subsurface: Imaging and monitoring through DAS measurement) is part of this dynamic. It explores the use of telecom optical fibers as permanent and ultra-dense seismic sensor networks. These technologies, based on distributed acoustic sensing (DAS), enable the transformation of existing optical fibers into subsurface imaging and monitoring tools.
Expérimentation sur le campus de Nantes de l’Université Gustave Eiffel.
© PEPR Sous-sol, bien commun
Why telecom optical fibers?
Traditional seismic imaging methods are limited in urban environments due to access difficulties, small-scale subsurface heterogeneities, and electromagnetic noise interference. Telecom optical fibers offer an innovative solution:
- Reduced cost: utilization of existing telecom infrastructure.
- Continuous monitoring: ability to track subsurface changes over long periods.
- High resolution: up to 2 meters (with a range of 50 km).
- Insensitivity to electromagnetic noise.
- Accessibility: single measurement device connected to one end of the optical fiber.
A promising initial experiment
An initial experiment in a controlled environment was conducted in a peri-urban setting on the Nantes campus of the Université Gustave Eiffel. On a 600 m² geophysical site with a depth of 6 meters, 600 meters of optical fibers were temporarily deployed on the surface. Two types of fiber-to-soil coupling were tested:
- Fiber laid on the ground (coupling of the fiber and soil through the weight of the optical cable).
- Fiber laid on the ground and covered with a 10 kg sandbag (coupling of the fiber and soil through additional ballasting along with the weight of the optical cable).
Two vibration generation methods were tested: a hammer and a vibrating pot. The results show that optical fibers can provide high-quality imaging, even at small scales (5-100 m), paving the way for geotechnical applications and monitoring urban infrastructure in the near subsurface.
Next Steps: Toward Real-World Application
The URBIDAS project now plans to test these technologies in real-world urban conditions, in collaboration with existing operators. The goal is to evaluate the feasibility of using optical fibers for subsurface monitoring on existing urban networks.
These advancements will contribute to better management of subsurface resources, particularly for applications such as geothermal energy, energy storage, seismic risks, or urban planning.
A Step Toward Sustainable Subsurface Management
The URBIDAS project illustrates how technological innovation can transform our understanding and use of the urban subsurface. These technologies enable us to move toward more responsible and sustainable management of underground resources, essential for the energy transition and the development of future cities.