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Neasden Super Scheme

Description of Works
The A406 North Circular Road remains one of London’s busiest A-roads. At peak capacity, it experiences traffic volumes only 10 per cent lower than the M25. The Iron Bridge and the Dog Lane Arches in Neasden are two of the most important structures along this strategic road. 

They carry the A406 across the Jubilee and Metropolitan lines, while also carrying mainline rail lines into London. Disruption to the transport network was unavoidable during the works, but Transport for London (TfL) wanted to ensure that it was kept to a minimum.

TfL commissioned FM Conway to carry out three key schemes on the A406: the renovation of the Dog Lane Arches; the refurbishment and lifting of the Iron Bridge; and the rebuilding of the retaining wall on Dog Lane itself.

Delivering Innovation

The first part of the project was to apply new waterproofing systems to the upper parts of the Dog Lane Arches and repair any areas where the concrete had been damaged. This required the phased closure of the westbound lanes of the A406, carried out in two stages.

Tom Chipperfield, Contracts Manager at FM Conway, explained:
"We established a contraflow system and took the A406 from three lanes down to two, treating each lane in turn, we carried out the required waterproofing works and resurfaced the closed carriageways."

Tom adds: "Alongside the Dog Lane Arches work, we simultaneously began key works on the Iron Bridge overhead. Part of the Iron Bridge element of the project was a simple repainting and refurbishment job. However, because the low-lying structure used to cause problems for larger HGVs, TfL also wanted us to use this opportunity to raise the bridge."

Much of the project was self-delivered by FM Conway’s own teams, with street lighting works, civil engineering, traffic management and surfacing all carried out in house. FM Conway’s own range of construction materials was also used across the project. But while this streamlined the supply chain and made rapid delivery much easier, there were still multiple stakeholders that needed to be engaged throughout the project.

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Due to the strategic location of the scheme and the potential disruption it would cause, great care was needed to respect the specific needs of all stakeholder groups.

Tom Chipperfield - Contracts Manager at FM Conway

FM Conway’s team took the opportunity of the planned lane closures to install additional cross beams, lifting the bridge by 600mm. Larger lorries can now use this stretch of the A406, providing a significant boost to business in the area.

“Due to the strategic location of the scheme and the potential disruption it would cause, great care was needed to respect the specific needs of all stakeholder groups,” says Tom. “Access to the doctor’s surgery at the local Brentfield Medical Centre, for example, was affected by the works, so we put special measures in place to enable doctors to get in and out quickly in a medical emergency.”

Challenges and Solutions

In addition to the logistical challenges associated with a busy programme of multiple works, there were several complex engineering issues to contend with. 

The Dog Lane Arches is located immediately above both the Jubilee and Metropolitan lines, and London Underground needed assurance that the track lines below would not be damaged by overloading the road. The solution came in the form of truck-mounted HIAB units. Lighter than standard cranes, these units allowed the team to move heavy materials into place without breaching weight limits.

Weather conditions during the project added challenges. Although unseasonably dry weather in the lead up to Christmas helped speed up the concrete and waterproofing works, the high winds experienced during this time created problems for the Iron Bridge works.

Tom explains: “On two occasions we had to abort weekend works on the bridge for safety reasons. However, because we had been able to deliver concrete and waterproofing work quickly, we were still able to complete that phase of the project on time overall.”