Innovative Freezing Solutions for the Paris Underground
Challenging ground conditions and limited space in metropolitan Paris required the use of a ground freezing technique instead of conventional methods such as soil mixing and jet grounding for stabilisation and sealing works. Thus, ground freezing was applied at the “Vert de Maisons” train station for the construction of a vaulted ceiling needed for the excavation of a mezzanine tunnel, as well as for the construction of a 75 metre long and frozen bottom plate to stabilize the ground. In total, around 150 freezing boreholes with individual lengths ranging from 8 to 78 metres were drilled, amounting to approximately 4,500 metres overall. Other applications within the project included the construction of a connecting tunnel from the metro to a mine shaft and creating underground links between a railway station and adjacent buildings.
Our Services
Between 2015 and 2021, CDM Smith was commissioned by several construction firms and planning agencies to carry out laboratory testing of frozen soils and provide consulting services. In addition to soil-mechanical categorization tests, mineralogical trials and chemical analyses (salinity) we also performed uniaxial and triaxial compression and creep tests at various temperatures on undisturbed drill core samples as well as on artificially reprocessed soil samples. As ground freezing was applied in close proximity to existing underground constructions and overground infrastructure and buildings, frost heave and frost pressure tests were necessary to evaluate the impact of those freezing measures on existing structures.
Planning and Consulting based on Laboratory Values
Based on our laboratory results we were able to derive static and thermotechnical parameters for various formations. These formed the basis for the static assessment of the frost body and the thermotechnical evaluation to determine the frost body’s chronological development and the required energy. During the planning phase of the freezing measures, CDM Smith advised different contractors on the design and selection of the most appropriate freezing technique.
Did you know?
The project is backed by Société du Grand Paris, a national company responsible for the conception, design and implementation of the Grand Paris Express. The Grand Paris Express aims to become a fully digital metro system. The project's goal is to improve connections between Paris's three airports, various business districts and scientific centres, as well as to reduce the use of private cars in favour of public transport and create better connections between work and residential areas.
