 Aktuelle Projekte / Bois de Peu Tunnel, Besançon - France
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During the construction of the southern by-pass of Besançon, several structures, including two tunnels were built in the section Mercureaux.
The joint venture "Tunnel du Bois de Peu" began driving two 500 m long tubes in August 2005. An exploratory gallery providing geological information revealed two sections that could cause difficulties during the driving of the tubes:- A zone consisting of an alternation of marls and limestone in the tunnel section PM 325 m. Excavation of the section was done by the drill and blast method.
- A zone consisting of brittle clayey marls in the section of the portal Vallon (PM 500 m). This zone was built with steel arches and shotcrete together with a reinforcement of the tunnel floor. Excavation was done by crown drive.
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| Longitudinal section of the Tunnel Bois de Peu and geological structures in the plane (Source : www.contournement-besancon.com) |
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| Solexperts AG was contracted by "Tunnel du Bois de Peu" the joint venture to instrument three geotechnical cross- sections. The sensors are linked together by the Solexperts GeoMonitor data acquisition system. One of the cross-sections, situated in the region TM 325 m of the descending tube, is equipped with Solexperts six-point modular extensometers for the measurement of absolute displacements. Two additional cross-sections located at the "Vallon" tunnel portal are equipped with Solexperts modular extensometers, earth pressure cells at the contact rock/lining and vibrating wire extensometers on the lining and in the inner concrete shell. |
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| View from the portal "Vallon" towards the descending tube with the instrumented reinforcement of the tunnel floor at the time of the breakthrough |
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Installation of the vibrating wire extensometers before the emplacement of the shotcrete shell |
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Additionally, the extrusion of the tunnel face during the driving is surveyed with Sliding Deformeters. The aim of these measurements is to determine the displacement of the tunnel face (extrusion) during the driving related to the number of anchors and the quality of the rock mass.
The GeoMonitor data acquisition system allows the operator (D.D.E. - Direction Départementale de l'Equipement) to view measurements in real-time and evaluate the behaviour and long-term stability of these problematic zones. The technical quality, field experience and flexibility of the Solexperts team adds to the success of the instrumentation and monitoring during the on-going tunnel driving. |
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| View of the tunnel face with anchors |
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| In addition to the above instrumentation, the C.E.T.U. (Centre d'Etude des Tunnels in Lyon) measures strains on fibre glass anchors in the tunnel face using 2 Solexperts loggers. These two loggers were delivered and installed by Solexperts AG and are placed at the rear end of the borehole and retrieved during the on-going driving. |
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| Completely equipped reinforced cross-section. |
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| Measurement |
Instruments and Specifications |
| Absolute convergence |
10 Solexperts six-point modular extensometers.
Length : 10 m
Range: 100 mm |
| Deformation on steel arches |
28 welded vibrating wire extensometers
Range : 3000 µm/m |
| Deformations in the inner concrete shell |
28 vibrating wire extensometers encased in concrete + 2 test specimens
Range : 3000 µm/m |
| Earth pressure at the outer wall |
16 earth pressure cells at the contact rock/lining
Range : 1.7 MPa |
| Data acquisition system |
Central GeoMonitor with 7 memory interfaces in the tunnel.
A total of 172 sensors |
| Extrusion during driving |
60 m Sliding Deformeter casings.
Accuracy : 0.01 mm |
| Anchor strain |
2 data acquisition systems at the rear end of the borehole, retrievable during the driving. |
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