Digging Deep in Complex Ground: The Geotechnical Challenges of Saint-Cloud Station (Grand Paris Express Line 15)

Abstract:

This presentation focuses on the geotechnical challenges and construction methods associated with a deep metro station of the Grand Paris Express, located on the western section of Line 15. Built on the slopes overlooking the Seine valley, the station is situated in a dense urban environment next to numerous infrastructures including railway tunnels, hospital facilities and historic retaining structures. These constraints require strict control of ground movements and construction impacts by the geotechnical and monitoring team of the Line 15 project.

The geological context is representative of the Paris Basin stratigraphy, with heterogeneous formations including Lutetian limestone and plastic clays (Argiles Plastiques) layers overlying deeper chalk formations. The hillside is also characterized by historical instability, through the potential creep of clay formations toward the Seine and the resulting detachment of the limestone blocks. Furthermore, the presence of historical underground works and former limestone quarries increases the geotechnical complexity of the site.

To address these conditions, an extensive ground investigation campaign was carried out, including more than fifty boreholes and exploratory drilling reaching depths up to 80 meters. The station is constructed using deep diaphragm walls reaching approximately 55 meters in depth and anchored into the chalk to ensure global stability and limit ground movements. This case study illustrates how geological conditions, urban constraints and structural design interact in the construction of deep metro stations within the Grand Paris Express program.

Short bio:

Nicolas Walbrecq is a geotechnical engineer specialized in the design of geotechnical structures and geotechnical engineering. He has worked on major civil engineering projects in France and abroad, notably the Grand Paris Express Line 15. He is currently Head of the Design Office at Botte Fondations, part of VINCI Construction, where he leads engineering activities related to foundation systems and complex geotechnical structures.

Mélaine Bommertz is a geotechnical engineer at Dodin Campenon Bernard, part of VINCI Construction, a civil engineering company specialized in major infrastructure and underground construction projects. Graduated from the École Nationale des Ponts et Chaussées, she works on large-scale infrastructure developments including the Grand Paris Express. Since 2024 she is involved in the Line 15 project in geotechnical analysis, site follow-up, monitoring, and the adaptation of construction methods to ground conditions.