164
H.Grann
Fig. 15.4. Tie-in chamber installation site and catamaran vessel
15.5.5
Pipelaying in the Tunnel
After recovery and dismantling of the boring machine and the tunnel jacking facilities,
a welding station was set up on-shore in front of the tunnel entrance shaft and the two
approximately 250o-m lengths of 4o-in. parallel pipeline were gradually welded and
hauled through the tunnel from the tie-in chamber (see Fig. 15.6). Upon completion of
this job, the tie-in between the two off-shore and on-shore pipelines was made, the tiein chamber was cut to a level of 2 m below the seabed and both the tunnel and the
remaining part of the tie-in chamber were filled with a special temperature-stable concrete mixture.
15.5.6
Backfilling of the Dredged Material
After completion of the pipelaying and the tie-in operations in the tie-in chamber, the
trench and the access channel were backfilled with sandy material from the interim
storage area. Backfilling took place by means of trailer suction hopper dredgers of different sizes, depending on available water depth. The material dumping was carried
out in a controlled manner using discharge pipes to avoid dispersion and loss of material in the strong tidal currents. The total amount of sand being backfIlled was approximately equivalent to the amount of material being dredged; thus, the mass balance in
the system was re-established, which was one of the conditions given in the authority
permission.
H.Grann
Fig. 15.4. Tie-in chamber installation site and catamaran vessel
15.5.5
Pipelaying in the Tunnel
After recovery and dismantling of the boring machine and the tunnel jacking facilities,
a welding station was set up on-shore in front of the tunnel entrance shaft and the two
approximately 250o-m lengths of 4o-in. parallel pipeline were gradually welded and
hauled through the tunnel from the tie-in chamber (see Fig. 15.6). Upon completion of
this job, the tie-in between the two off-shore and on-shore pipelines was made, the tiein chamber was cut to a level of 2 m below the seabed and both the tunnel and the
remaining part of the tie-in chamber were filled with a special temperature-stable concrete mixture.
15.5.6
Backfilling of the Dredged Material
After completion of the pipelaying and the tie-in operations in the tie-in chamber, the
trench and the access channel were backfilled with sandy material from the interim
storage area. Backfilling took place by means of trailer suction hopper dredgers of different sizes, depending on available water depth. The material dumping was carried
out in a controlled manner using discharge pipes to avoid dispersion and loss of material in the strong tidal currents. The total amount of sand being backfIlled was approximately equivalent to the amount of material being dredged; thus, the mass balance in
the system was re-established, which was one of the conditions given in the authority
permission.