The Boulou Fault Zone Its Geology and its Impacts on the Perthus Tunnel project The Boulou Fault Zone Eastern Pyrenees, France Its Geology and its Impacts on the Perthus Tunnel project Jonathan GERTHOFFERT Marc-Stéphane GINOUX 10/05/20151

CONTENTS Localisation Geology Hydrology Impacts on the Perthus Tunnel Project Solutions 10/05/20152

Localisation Eastern Pyrenees - France/Spain border High speed railway project between France and Spain  Perthus Tunnel excavated under the Pyrenees  Bitube km long  Excavation from the South to the North with TBM designed for good quality rocks 10/05/20153

Geology The Boulou Fault zone:  Part of a large ductile shear zone  25 km long  Dip to the North  Dip angle between 50˚-70˚  Crossed perpendicularly by the tunnel over a distance of 50 meters 10/05/20154

Geology 5 FRANCE SPAIN Pyrenees Source: SEA CONSULTING

Geology Rock composition from the South to the North  Gneiss  Weathered Gneiss  Gneiss Gouge  Fault Gouge  Schist Gouge  Weathered Schist  Schist Top soil  1m deep, clay, fault gouge, very fractured 10/05/20156

Geology 7 FAULT ZONE Stream Source: González et al.

Hydrology High groundwater level Stream at the surface Links with deep thermal sources Abundant presence of clay in the fault gouge due to an old thermal water circulation over the fault plan >>> Fault zone has a low permeability and saturated soil 10/05/20158

Engineering aspect Very bad rocks and low depth excavation (~15 m)  High risk of overexcavation and cave-in  Important settlements at the surface  High risk of water infiltrations  Living area above the tunnel Interception of the geological structure producing thermal sources  Risk of important modification of the aquifer 10/05/20159

Engineering aspect Site investigation to study the Fault zone  Excavation of an experimental gallery  Analysis of the soil thanks to in situ and laboratory tests  Pressuremeter, triaxial tests, …  RMR, compressive strength, …  Hydrological study  In situ : piezometer  Chemical Analysis and flow rate measurements in the thermal baths Modelling and calculation of the soil behaviour and validation with the excavation of the experimental gallery 10/05/201510

Solutions Water Pumping from experimental gallery and 5 water wells to drain groundwater  No infiltration during tunnel excavation Realization of a concrete trench to protect and divert the stream  Environmental protection Jet grouting from the surface and the TBM  Reinforcement of the soils : better mechanical properties allowing excavation Constant speed and medium pressure of the TBM cutting head applied on the rock face 10/05/201511

Conclusion Geologic, hydrologic and topographic surveys during the crossing of the fault The fault zone was crossed successfully  Very low settlements  No overexcavation  Preserved site 10/05/201512

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