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Contract 1. Redbridge (J4) to Loughton (J5)

Close liaison was maintained with the local authorities, police and other interested parties during the planning and design stages. Anticipating publication in November 1972 of the Government White Paper entitled "Development and Compensation: Putting People First", the DoE in conjunction with the GLC and local authorities embarked on a detailed study of further measures that would reduce the impact of such projects on the environment. Contract 1 of the M11 was thus the first motorway constructed to incorporate the provisions of the White Paper.

Environmental considerations were very much to be desired. Contract 1, being largely urban, has undeniably affected the lives and amenities of local residents to a great extent - but it could have disrupted them entirely. No less than 27 structures comprising viaducts, bridges and subways were built on this section of the motorway. In addition, electricity, water and gas services were altered, electricity pylons and main sewers resited, and the River Roding diverted in three places. Consequently, extensive efforts had to be made to minimise the impact on residents and their amenities. Restrictions were applied on haulage routes for incoming and outgoing material; minimal use of public roads was permitted for moving excavated soil; access to the site was confined to specific locations; and most important to the local residents maximum noise levels for construction plant were established and implemented.

Other remedial measures included the siting of noise barriers, the provision of sound insulation to private dwellings in the vicinity of the motorway, landscaping motorway embankments with large-scale plantings of trees and shrubs (augmenting the GLC proposals for the Roding Valley Linear Park), the introduction of additional accesses below the motorway to permit unrestricted movement from one side to the other, and reasonable compulsory purchase and additional compensatory payments to owners and tenants whose homes or other property have been lost through or adversely affected by the construction.

Contract 1 was let in October 1973 to W&C French (roadworks) and Kier (structures). It extended through the flood plain of the River Roding from the southern terminal with the A12 in Redbridge to a partial interchange with the A1168 in Loughton. It crossed over London's A406, one of the busiest roads in Britain, to form the Woodford Interchange, which linked the M11 with the A406 and incorporated provision for further roadworks in the future.

London-Cambridge MotorwaySix viaducts occurred at this interchange. They carried two kilometres of elevated sliproads, and ranged from a 14-span, 453 metre long viaduct to one of eight spans and 243 metres long. All occurred on horizontal and vertical curves and carried a two-lane, 7.3 metre wide carriageway. The remaining 5.6 kilometres of Contract 1 running northwards to the interchange at Loughton consisted of a dual, three-lane, 11 metre wide carriageway.

For five of the viaducts, 49 of the 55 deck spans required were formed from a total of 539 precast, pretensioned concrete M beams. A special in-situ concrete integral crosshead over the piers was developed to overcome the problems of establishing beneficial deck continuity, the variables imposed by the horizontal and vertical curvatures in the essentially standard deck spans, and the closure of the gap between the longest M beam available and the greater length optimum span utilised.

The original specification laid down conditions for transporting the beams from railhead to site. In the event, however, the contractor's alternative proposal of casting them adjacent to the site and thus avoiding severe transportation problems was accepted. But to cast so many M beams at site was a major undertaking unmatched by previous experience. Further, all beams required deflected tendons, and special equipment for this purpose had to be developed and installed in the casting beds. Beams were in two sizes, 29 metre long for standard spans and 24.5 metre long for end spans; each size was 1.2 metres deep and weighing 27 and 23 tonnes respectively.

The vertical profile of the Contract 1 motorway was influenced by the need to keep the carriageway formation above river flood level whilst maintaining a minimum height above ground level roads. Hence the viaducts. In the flood plain the embankments carrying the motorway rose to nine metres, and the only sections of cutting were at the western limit where an existing A406 cutting was widened, and a 3.2 kilometre length north of Woodford Bridge where the route curves away from the river through higher sloping ground.

Approximately 1.1 million cubic metres of predominantly London clay, renowned for its unmanageability, were excavated for compaction into embankments. Much of it came from the huge cutting which forms the Chigwell Service Area, two kilometres from the start of Contract 2 at Loughton. The motorway ran straight through what was the Chigwell Council tip and the rubbish accumulated there over 30 years had to be removed. The slopes were overdug, then backfilled with clay to stabilise them. More soil for filling came from an improvement scheme on the A406 at Waterworks Corner, close to, yet unconnected with, Contract 1 but operated by the same contractor, W&C French (Construction) Limited.

The various structures of Contract 1 comprised, in addition to the six multispan viaducts already mentioned, three overbridges and two underbridges for road crossings, five river bridges, one accommodation overbridge, three accommodation underbridges and six pedestrian subways. A new bridge carrying the London Transport Central Line over the motorway was built under an advance contract designed and supervised by London Transport. All of these structures were of prestressed or reinforced concrete.

Meanwhile, the River Roding continued to meander along the general line of the motorway in Contract 1 and at the southern end of Contract 2. To minimise the need for structures over the river and also the risk of flooding in the future, the Roding was diverted in a few places. As one of the older residents in the vicinity pointed out, this was not the first time the river had been diverted and at Woodford Bridge in Contract 1, it was diverted back into its former bed! But there was now little risk of flooding, and less possibility of damage if it should ever recur.