THE PROBLEM
The southern approach road entrance and exit ramps were routed in a cutting excavated through the silty clays and gravels of the river bank and flood plain. Importantly there was minimum land available to accommodate the radius of the slip road, so near vertical earth retaining structures of up to 8 metres high were needed, which required a low environmental impact and high aesthetic appeal .
THE SOLUTION
The Tensartech TW1 Earth Retaining System was used to construct two reinforced soil retaining walls, one of which at 200m long is one of the longest of its type in the UK.
PROJECT DESCRIPTION
The £260m New Tyne Crossing project, administered by Concessionaire TT2, is building a second vehicle tunnel beneath the river Tyne, between East Howdon and Jarrow, to supplement the existing vehicle tunnel, pedestrian and cycle tunnels. This major project, which will be managed until 2037, is one of the most important transport infrastructure projects currently under construction in the UK. In addition to the new tunnel, the existing vehicle tunnel will be extensively refurbished, a toll plaza built at the north entrance and a completely redesigned southern entrance and interchange at the entrance to the existing tunnel. Because these entrances represent the visible part of the tunnel after the cut and cover sections and immersed tubes are completed, great care has been taken in their design, construction and finishing. It was important to liaise with the near-by residents whose houses border the southern entrance construction and to leave them with a high quality installation which has maximum aesthetic appeal. Tensar International was awarded the design and supply sub-contract for the reinforced soil retaining walls.
“The Tensartech solution was chosen as it can use site won materials (gravels, silts etc) instead of high cost imported aggregates for the retained fill,” commented Senior Engineer Sebastien Richard of Bouygues TP. “This minimises the transportation requirement, and uses much less concrete than more conventional retaining walls, which also saves site time and equipment.” The project achieves excellent sustainability credentials with an attractive textured finish, within rapid construction schedules and a tight budget. The aesthetically pleasing, split face modular TW1 blocks, supplied here in two pigmented versions of flint and pewter, are dry laid by hand, without the need for a mortar. Because of this and the lack of insitu concrete, curing time is eliminated and the structure is immediately trafficable and ready for pavement construction of the slip road.
