PRESTONS ROAD FLYOVER

The Prestons Road Flyover carries the East India Dock Link  highway over a grade-separated junction built over the line   of the Blackwall Tunnel. The line of the highway lies   between the cast-iron lined, bored tunnel and the brick-built   cut-and-cover approaches. Potential differential movement   of the tunnel due to surcharge loading at that point was   unacceptable. 

The typical geology of the London Docklands comprises a   variable depth of made ground overlying compressible   alluvial materials which in turn overlie the London Clay. The   design challenge was increased by the constraints of the   grade separation geometry and the proximity of an elevated   section of the Docklands Light Railway.  

The avoidance of surcharge on the tunnel and the potential  for differential movement were resolved by supporting the   approach ramps on piles. The embankment loads were   transferred from the ramp fill to the piles by a granular   mattress reinforced with high-strength Paralink geosynthetic   reinforcing materials. 

Additional economy was achieved by the use of lightweight   pulverised fuel ash as the fill material. The durability of   Paralink in these chemically aggressive conditions made it   an obvious choice for the application.