Moving Mary

When the UK National Grid was awarded the £100m contract to excavate a 5km tunnel under the River Humber to carry a replacement gas pipeline, the project involved transporting a German-built tunnel boring machine (TBM), by road, from Immingham Docks to Goxhill, north Lincolnshire.

Fracht AG designed a transport solution from Germany to Rotterdam, where the machine, named Mary, was loaded for onward shipment to Immingham.With 18 months to go before Mary’s arrival at Immingham, Fracht UK and Collett & Sons worked in collaboration to devise a plan for the onward road journey.

The machine consisted of four components: the 30t cutter head, 4.8m long by 4.5m high and wide; a 70t shield that was 4.5m long; a 95t machine can (at 9.6m the longest and heaviest load); and a 20t tail shield. On arrival at Immingham, each was surveyed and then loaded onto Collett’s awaiting trailers.

The cutter head and the shield set out first. Many tight bends and turns needed to be negotiated on the 27mi route. The total rigid length of the largest loaded trailer was 29m; the combination tractor and trailer unit measured 40m.

For this reason Scheuerle selfpropelling powerbooster trainers were used. At tight or restricted-space turns these are capable of being detached from the tractor unit and powered, with their load, by an on-board Power Pack Unit. Steering is done manually by a steersman on foot, via a wireless remote control unit. With it, the hydrostatic drive, lifting and hydraulic steering and brake systems, as well as the electric power supply are controlled.

The system can also act as a booster when connected to the tractor, giving additional power on gradients. Equipped with shiftable drive axles the system can be towed, as a normal unpowered trailer, at up to 80km/h; the power boost cuts in automatically when the tractor-trailer speed falls below 9mph (14km/h), eliminating the need for a second, pusher, tractor unit.

On this trip, however, restricted turning spaces rather than gradients were the main problem. One such point occurred at the Thornton Road and College Road crossroads in Barrow upon Humber, where the team faced an extremely tight left hand turn. The teams had already arranged the removal of five sections of Amco barrier, a concrete sign post, a blind summit sign and the complete removal and reduction of an entire splitter island, which was taken down to road level—and had also resurfaced the Northeast side of the junction with stone 3m from the kerb. To navigate this section of the route, the driver and steersman disconnected the air, hydraulic lines and drawbar coupling between the tractor and trailer and disconnected the tractor. Using the remote control unit the steersman manually manoeuvred the selfpropelled trailer module, successfully negotiating it round the intricate and difficult bend.

The tractor unit was re-attached, and the journey continued. For the loads to go through Goxhill’s residential area, parking restrictions were in place and trees were pruned to give a clear envelope 5m high and 5.5m wide. At the Ferry Road Rail Bridge the trailer’s hydraulic suspension was raised to allow the low deck to safely clear the crest, whilst the entire combination was manoeuvred at crawl speed in the centre of the carriageway until clear of the structure. Leaving Goxhill the heaviest load again required the tractor to be disconnected and the trailer to be manually steered, using PowerBoost.

The final approach to the delivery site also required extensive roadway modifications. Temporary road signs were removed, loose items were cleared from the site and five separate areas of grass verge were resurfaced. The average width of the East Marsh approach road was 2.8m, below the 3m axle width of the loaded components. The teams had placed 30m of plating from the junction onwards, followed by 30m of hardcore, to ensure vehicle and trailer stability on this narrow section of track. The entrance to site had been widened and the site gates dismantled. Three and a half hours after leaving Immingham the cutter head and shield were delivered.

After unloading, the empty trailers left the site, under police escort due to their size. The following day, the tail shield and machine made the journey. Once assembled, Mary will be used to build a tunnel under the Humber to take a replacement high pressure gas pipeline. The pipeline will replace the one which lies on the riverbed. Due for completion in 2019, once built it will be the longest gas pipeline in a tunnel, inserted in a single string, in the world.