Tunnel Breakthrough

Design and build contractor, Bouygues Travaux Publics, broke through the remaining concrete diaphragm wall at the end of the final section of Sprayed Concrete Lining (SCL) tunnel in Jarrow this month. Removal of this underground wall completes the excavations for the land tunnel through Jarrow making it possible to walk from the south junction all the way to the river section of the tunnel.

tunnel breakthrough image

Representatives from the New Tyne Crossing’s project promoter, the Tyne and Wear Integrated Transport Authority (TWITA), Concessionaire TT2, and Bouygues Travaux Publics watched the final diaphragm wall being demolished.

Cllr David Wood, Chair of TWITA, said: “This is an exciting milestone for the project and I am very proud to see the land tunnel through Jarrow opened up. It is incredible to think that the first dig to create the tunnel trench happened around a year and a half ago, and we are already refilling the trench above the new tunnel with the soil we removed. The process has gone very smoothly and I am delighted with progress.”

Trevor Jackson, Managing Director of TT2, said: “This is a tremendous moment for everyone involved in the project.  There is still work to do to complete the tunnel structure, but to be able to walk from one end of the land tunnel to the other beneath Jarrow really gives a sense of achievement and brings us one step closer to opening the new tunnel to traffic.

“I would like to take this opportunity to thank the local community and also TT2’s customers, who have been very patient throughout the building works.”

Fabrice Cao, Section Manager for Bouygues Travaux Publics, said: “I am very happy to have reached this stage in construction. The SCL sections have brought particular challenges and have required some sophisticated measures to enable us to complete them. It has been hard work to build this part of the tunnel but it has undeniably been worth the effort as it has prevented major utility diversions.”

The new vehicle tunnel comprises two short sections of SCL, equating to approximately 4% of the land tunnel excavations (32 metres and 40 metres long). SCL techniques were adopted in two locations in Jarrow in order to avoid lengthy diversions for a combined sewer and a gas main that cross the site.

The river section of the tunnel was built using immersed tube technology. The bulk head walls separating the four river tunnel units are currently being demolished. Once these have been fully removed there will be uninterrupted passage from one end of the tunnel to the other. It is anticipated that this milestone will be reached by early July 2010.

Picture: At the mouth of the final section of Sprayed Concrete Lining tunnel as the final underground diaphragm wall is demolished.

From left to right: Andrew Coapes, Technical Manager, TT2; Fabrice Cao, Section Manager, Bouygues Travaux Publics; Trevor Jackson, Managing Director, TT2; Cllr David Wood, Chair of the Tyne and Wear Integrated Transport Authority.

Notes

1. The SCL sections use a technique to mechanically excavate the tunnel beneath the ground and reinforce the excavation at the same time, using sprayed concrete.

2. The majority of the land tunnel either side of the Tyne was built using a technique known as “cut and cover”, which involved excavating a deep trench, constructing the tunnel at the bottom of the excavation, and then backfilling with soil. The cut and cover excavations were completed in October 2009.

3. The sections of cut and cover tunnel and SCL tunnel are separated by temporary underground concrete “diaphragm” walls whilst construction work takes place. Structural work on the first SCL tunnel, located in Jarrow’s Riverside Park, was completed in December 2009. The demolition of the final SCL diaphragm wall marks completion of the main structural works for the SCL tunnels.