Subsea tunnel boring machine lifted with Modulift beam

23 February 2018

Stockton Drilling completed multiple subsea lifts of a 28t, 18m-long tunnel boring machine (TBM) at an offshore wind farm, using a custom lifting beam, slings and shackles supplied by Modulift.

The lifts were completed at the Beatrice Offshore Windfarm/Direct Pipe Landfalls (BOWL) in Portgordon, Scotland.

Stockton’s involvement included the trenchless installation of two independent 48in x 450m steel landfalls for high-velocity cables, using the DirectPipe system and AVN1000 micro tunneling machine from Herrenknecht. DirectPipe is a hybrid micro-tunnelling and pipe-jack system that lines the tunnel as it advances.

The TBM was recovered from the sea after each drive using a remote disconnect module—the first time the approach had been used worldwide, said Modulift. Divers were then dispatched to the TBM’s location to attach the 34t-capacity, 16.6m-long beam to a 120t-capacity crane, positioned on a rented jack-up barge. The TBM was then lifted out of the water and placed on a multi-cat for return to Buckie Harbour.

Modulift was required to design and manufacture a below-the-hook solution to lift the TBM from beneath the surface of the water, where it was positioned four degrees from horizontal. The TBM comprises ten modules each with their own individual lifting points, all of which were used to provide equal loading and to enable the machine to be lifted in one piece. The beam also had three top-lifting points to facilitate rigging the crane.

The company also used counterweights to tilt the unloaded beam to the same inclination as the seabed, ensuring all the bottom connections were carrying load.