JUNCTIONS AND BREAKTHROUGH
THE TOPOGRAPHY IN THE TUNNEL:
A SUCESSFUL JUNCTION UNDER SEA:
Starting 38 km distance apart on two sides of the channel following a path with hollows and bumps, the TBMs found themselves exactly face to face following a precise mastery of the topography.
A JOINT ANGLO-FRENCH TOPOGRAPHIC BASIS UTILISING AMERICAN SATELLITES
French and English topographical systems were not correlated with each other in altimetry with a suggested discrepancy of 44 cm between their respective ‘zeros’.
12 stable geodetic points have been chosen in France and England and the Global Positioning System (GPS) was selected to receive signals from the atomic clocks of 18 U.S. Navstar satellites on French, English and American receivers parked on the 12 points with an accuracy of 10-6.
Triangulation led to the establishment of landmarks on each side of the channel, the transposition of these landmarks into the shaft and the installation of benchmarks every 50 metres into the completed tunnels, forming bases of control every 400 metres.
AN EXCEPTIONAL RESULT:
The under-land TBMs emerged less than 2 cm from the axis of both the previously constructed portal of Beussingues in the Terminal and the shaft.
The under-sea service tunnel TBM, after more than 15.6 km of boring toward its British equivalent, checked the relative positions of the two machines when the distance between them was still sufficient for them to change trajectory so as to « rectify the situation », if needed.
To do this:
- The French and British TBMs stopped at 100 metres distance from the other.
- A small ‘pilot’ drilling was run from the UK TBM to check the relative positions of the two TBMS.
- The difference measured between the theoretical axes of the tunnels was only of 358 mm horizontally and 58 mm vertically. This historic breakthrough has helped establish that the zero in England is 36 cm above the zero of the continent.
UNDER LAND TUNNELS:
28th OF APRIL 1989: THE UNDER LAND SERVICE TUNNEL
The first breakthrough on the French side was the breakthrough of the under land tunnel in the face of the Beussingues portal after having drilled 3 251 m from the Sangatte shaft.
The under land service TBM shield is the only one to have not been dismantled. It is now on view at Coquelles on a roundabout of the D243 near the Pierre Matheron square.
18th OF DECEMBER 1989: BREAKTHROUGH OF THE UNDER LAND SOUTH RUNNING TUNNEL
The breakthrough of the South under land running tunnel took place at the portal of Beussingues after having drilled 3 265 m.
This TBM was rotated on an air cushion at the portal to drill the north running tunnel from the portal to the Sangatte shaft.
29th OF NOVEMBER 1990: BREAKTHROUGH OF THE UNDER LAND NORTH RUNNING TUNNEL
The under land tunnels are then completed and the TBM is dismantled in the Sangatte shaft.
1St OF DECEMBER 1990: HISTORICAL SERVICE TUNNEL UNDER SEA BREAKTHROUGH
On the 1St December 1990 Graham Fagg for British team and Philippe Cozette for French team completed the break through in the last Gallery with Jackhammers, this was in the undersea service tunnel, between England and the Continent opening the fixed link …. And England was no longer an island…
To do this:
- After the verification of the topography survey, the British TBM resumes its normal progression for 40 metres.
- Then it deviates to the right out of the track and finally was buried in the concrete.
- The following ‘train’ of the two TBM’s are evacuated to the rear.
- The French TBM shield is dismantled, with its skirt still left in situ.
- A gallery of small section is dug allowing the stroke of Jackhammer of the historical digging.
- The lining of the tunnel is reconstructed by the installation of cast-iron rings.
26th OF MAY AND 28th OF JUNE 1991 BREAKTHROUGH OF THE UNDERSEA RUNNING TUNNELS
To that end:
- The British TBM is deflected downwards, under the French TBM and buried in the concrete.
- The French TBM bores in full face through to the British tunnel.
- The following train of the two TBMS trains is evacuated to the rear
- The French TBM shield is dismantled, its skirt still left in situ.
The south running TBM drilled 18 857 m and the north running TBM 20 007 m.