| Topic: | Engineers' view of what the tunnel construction would mean in Chiswick | |
| Posted by: | Thomas Barry | |
| Date/Time: | 14/02/15 23:12:00 |
| 'it was important to select portal locations that would allow for the continuation of traffic flow during construction. The location for the Western Portal was more constrained due to the road layout and the need to have it within close proximity to Hogarth Roundabout without making the alignment overly long and costly. The Western Portal, located 450m west of the junction between the A4 and Sutton Court Road, is 3 lanes in each direction and has a broad central reservation and crossing area allowing space for the portal and lanes in both directions for traffic flow. This location is also the required distance from the Fullers Brewery and the River to allow the tunnel to reach a suitable depth before the obstructions at a gradient of 4% or less. ... Due to the required size of the portals it may only be possible to keep one lane open for traffic; this would cause significant disruption to traffic. This could be minimised either by constructing the portals in two phases closing half the road at a time. This could also be achieved through top down cut and cover construction, where by the roadway could be reinstated during construction to reduce adverse impacts on traffic. It is possible to provide diversions around the open cut sections of the tunnel to re-join the route around Sutton Court Road junction where the cut and cover section begins. An estimated 150,000 lorry movements would be required for the removal of excavated spoil from the site. It is assumed that some of the excavated material will be retained on site and used to backfill above the tunnel, and lorry movements associated with this are not considered. It is likely that this spoil could be removed by river transport. A further estimated 40,000 movements will be associated with delivery of tunnel segments, concrete and other materials.' 450m west of Sutton Court Road is Harvard Hill, so presumably by 'allowing space for the portal and lanes in both directions' they mean widening it onto the park and taking a chunk out of the paths and grass either side. The width would need to be 40m, which is about twice the current three lane road (based on measuring the width over the sliproads coming up from Chiswick Roundabout. The total above ground worksite would extend from Harvard Hill right up to the Sutton Court Road junction. About half of it would be covered over eventually, although with significant above ground roads put on top. It's no wonder the cuddly artists impressions only show Hammersmith, isn't it? |