Sydenham By-Pass - Extruded Concrete High Containment Barrier

Project Summary

As a direct result of the Selby railway disaster in Britain, when a vehicle strayed off a road onto a railway line, resulting in one train colliding with another and causing 10 deaths, the Government’s efforts to help prevent a repeat saw the Sydenham Bypass, where road and rail systems run together, being identified as a high priority for preventative work with the high containment barrier.

Completed, the barrier will extend from Dee Street Bridge to the George Best Belfast City Airport exit tunnel and will also accommodate new street lighting columns and an anti-intruder fence.

The concrete barrier is a ‘high containment’ restraint system which will prevent vehicles from crossing through and onto the railway line. European tests have shown that the barrier will contain vehicles up to a 30 tonne tanker. An average sized car such as a Ford Focus weighs less than 2 tonnes, proving that the new concrete barrier will contain 4x4s, vans and coaches. Recently, a 30 tonne articulated lorry crashed into the central reservation on the M25 near London, was still unable to penetrate the concrete barrier.

The barrier is designed to last fifty years without repair or maintenance.

That project has been under way since early June, in a joint project between the Roads Service and Northern Ireland Railways, and a partnership charter between the clients, principle contractor Highway Barrier Solutions (a division of Rodgers Contracts Ballynahinch Ltd), Extrudakerb, consultant Peter Cole from Lincoln and Readymix NI. On schedule for completion within programme and budget for next month, the scheme involved the construction of a High Containment Safety Barrier along the length of the city-bound carriageway of the Sydenham Bypass.

Paul McEvoy, director of Highway Barrier Solutions, explained that the extrusion system being employed offered the best solution in terms of time and money. HBS is the local outlet for Extrudakerb’s concrete extrusion system.

“The project involved removal of the existing palisade fencing, the widening of the embankment and the installation of a Higher Vertical Containment Barrier – built to containment Class H4A – able to contain vehicles of up to 30 tonnes from encroaching onto the railway line” he told Equip.

“We required a very stable mix”

With HBS as the principle contractors working in partnership with Extrudakerb and Readymix Concrete, he revealed that the concrete design had taken four years to develop – to match the required height of 1.65m and slump of 5mm.

An added factor was the need to keep traffic flowing. The bulk of the concrete pours took place from 8.00pm-5.00am, allowing two lanes of traffic to remain open to carry the 50,000 vehicles a day that use the busy commuter route into and out of Belfast.

Traffic Management

HBS in house traffic management team looked after the traffic management on the scheme.
And, as the project moved towards the city, efforts were made to screen the extrusion machine to reduce noise. Paul McEvoy said that Belfast City Council officials had visited the site on a couple of occasions, checking that noise levels were within permitted levels. They were. The extrusion machine used was a Gomaco, the largest in Ireland, according to Paul McEvoy.

“The mould the concrete is extruded through is fabricated by Extrudakerb’s own in house designers. Readymix provided the concrete which was quality checked every 18 cu.m. – against a norm of about every 100 cu.m. A very high standard is required. The concrete base was specified with a strength of 30N and the high barrier with 35N which included polypropylene fibres. The concrete barrier in seven days would achieve an average strength of 40N, and after 28 days, it is hitting 65-70N,” he stated, explaining this was a result of the cohesive nature of the concrete mix and the extremely low water to cement ratio.

The extrusion process saw the concrete mix poured into a hopper, constantly compacted by nine vibrating pokers, before being extruded from the rear. The process was capable if producing 18 cu.m. per hour, or 25-30 linear m. per hour – much more economically than if shuttering and pouring had been adopted, said the HBS director. With the sensitive nature of the concrete mix, co-ordination with delivery to site and pouring into the mould was essential. Extrudakerb technicians monitored each delivery and analysed water content to very precise quantities.

The actual site was 2.3km long, and the barrier, in total, 2.1km in length. The £1.8 million contract also involves the mounting of street lighting on the barrier, from concrete build outs that allowed for maintenance without the need to gain possession of the railway track.

The concrete barrier is designed to last fifty years without repair as David Jones, director of Britpave, the organisation which promotes concrete barriers to the UK, explained the benefits further:

“Until now, roadside barriers have a need to be repaired or replaced following even minor accidents. This causes congestion as lanes are closed and reduced speed limits enforced. The concrete barrier does not need to be repaired; it requires no maintenance and has a shelf life of at least 20 years more than older steel barrier systems”.

Phase 1: Excavation and Base Extrusion

Phase 2: Extrusion of Main Barrier

New Concrete High Containment Barrier

Steel Parapets

Aluminium Parapets