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.

The The BoulouBoulou Fault Zone Fault ZoneEastern Pyrenees, France

Its Geology and its Impacts on the Perthus Tunnel project Its Geology and its Impacts on the Perthus Tunnel project

Jonathan GERTHOFFERT

Marc-Stéphane GINOUX

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CONTENTSCONTENTS

LocalisationGeologyHydrologyImpacts on the Perthus Tunnel

ProjectSolutions

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LocalisationLocalisation

Eastern Pyrenees - France/Spain border

High speed railway project between France and Spain

Perthus Tunnel excavated under the Pyrenees Bitube - 8.2 km long Excavation from the South to the North with

TBM designed for good quality rocks18/04/23 3

GeologyGeology

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GeologyGeology

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FRANCE

SPAIN

Pyrenees

Source: SEA CONSULTING

GeologyGeology

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GeologyGeology

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FAULT ZONE

Stream

Source: González et al.

HydrologyHydrology

High groundwater levelStream at the surfaceLinks 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

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Engineering aspectEngineering 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

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Engineering aspectEngineering aspect

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SolutionsSolutions 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

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ConclusionConclusion

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APPENDIXAPPENDIX

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