Robore uses Tyrolit sawing machines and consumables for demanding and high profile project
During construction of the new Tyne Tunnel in the North East of England, underground approach roads on the north and south sides were built using cut and cover techniques up to the river walls. The roads then had to be linked with the tunnel, which is of immersed tube design comprising four prefabricated caisson structures set into a deep trench in the river bed.
To allow this work to take place, main contractor Bouygues Travaux Publics constructed transition shafts on both banks of the river. South London-based controlled demolition and diamond cutting specialist, Robore was asked to devise a method for cutting an opening in the walls on the north and south sides down to the river bed, up to 26 metres below the high water mark, to allow the tunnel connections to be completed.
Jeff Lawrence, contracts director at Robore, commented, “The complex nature of the project deterred some wire sawing equipment suppliers from getting involved with us. Of the companies that were interested, Tyrolit emerged as the most experienced and able partner to assist us in getting the job done. During trials, its sawing machines proved very reliable and the latest electroplated diamond wire delivered good sawing speeds and cost per cut.”
It was decided that the south and then the north concrete walls would be removed in nine sections, each being cut full height and removed by sea crane, with the largest central key stone weighing in excess of 175 tonnes.
Initially, Robore diamond drilled all the wire feed holes and lifting holes, some up to two metres deep. This was done from within the transition structure in dry conditions. As each hole penetrated the wall below the water line, it was plugged to prevent the shaft from flooding.
Once the river bed had been excavated down to the level where the cut across the bottom of the walls was required, wire sawing commenced
using four remotely controlled Tyrolit SB wire sawing machines positioned on top of the south wall, above the level of the water at high tide.
Robore used specially constructed deflection pulleys designed by Tyrolit to transfer the direction of wire travel from the vertical plane to the horizontal, enabling the bottom cut to be executed. A dive master and two teams of 10 experienced divers, one on days and one on nights, were employed to locate and clear each of the wire feed holes and to thread the wire through the pulleys accurately in virtual darkness.
Tyrolit’s three-star DWM-C wire achieved above 1 m2/hr cutting speed and typically completed 21 square metres in a 24-hour period, allowing for time spent making adjustments and monitoring the cut. This was despite having to saw through concrete containing reinforcing bars ranging from 16 to 55 mm in diameter.
To overcome the initial problem of the wire drawing debris from the river bed into the cut and stopping the saw, the direction of drive was reversed to pull the wire out into the river, forcing the debris away. Up to 86 metres of wire was used to complete the cuts on the deeper south bank.
Next, Robore completed the vertical cuts, with the central key stone removed first so that the other eight could be lifted free without jamming. When cutting the centre section, the saws were set at a 45 degree angle from inside to out to enable easy removal of the key stone by river crane. Each subsequent vertical cut was a straight pull, with divers used at regular intervals to verify cutting positions and move temporary supports as required.
Over the course of a week, all of the remaining eight sections on the south side were similarly removed. Work was carried out in severe winter conditions, with snow driven by winds of over 50 mph and temperatures during the night dropping to minus 7 degrees Centigrade. The project was therefore not only technically difficult but physically demanding as well.
