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Sydenham Bypass (Northern Ireland) High Containment Safety Barrier
Although not a Concrete Step Barrier, Sydenham Bypass High Containment Safety Barrier was a complex, high profile
project, with physical constraints which had to be considered by the Contractor and incorporated through the entire Design and Construction process.
Our innovative solution for extrusion of a high containment concrete barrier provided the quickest construction method to minimise road and rail disruption, whilst providing full containment properties. Our design permitted for lighting and security fencing to be integral with the barrier. Although the extrusion of concrete barriers is relatively common, the size requirements of a high containment barrier make the process much more difficult. In fact, Sydenham Bypass was the first barrier of its type in Ireland.
The success in this project was dependent upon all the organisations involved, with HBS (Highway Barrier Solutions), Extrudakerb and Peter Cole Consultants forming a highly collaborative design and build team.
Health and Safety was paramount on this project, with Traffic Management and Railway Safety being coordinated constantly throughout the project.
BACKGROUND
Following the Selby railway disaster, when a car strayed off the road and onto a railway line, the Government’s efforts to help prevent a repeat incident saw the Sydenham Bypass being identified as a high priority for preventative work.
The client used a performance specification for a ‘High Containment H4a’ restraint system, allowing HBS to propose a product and method to suit the site specific requirements.
The project required substantial site clearance, removal of contaminated material and design and construction of a new foundation and barrier incorporating full technical approval. An anti- intruder fence and integrated street lighting mounted on the barrier from concrete build outs permitted maintenance without the need to gain possession of the railway track.
Project Partnering was essential to programme and coordinate the construction work, in particular the removal of excavated material and continuous concrete supply during night closures permitting the safe operation of the road and rail network during peak periods.
INNOVATION
Completed within programme and below budget during October 2006, the scheme involved the construction of an extruded Concrete High Containment Safety Barrier along the length of the city-bound carriageway of the Sydenham Bypass. The slipformed concrete barrier system employed by HBS offered the only practical solution in terms of time, disruption and cost.
This type of High Containment Barrier had never been constructed in Ireland and as the concrete mix is critical, a good relationship and understanding between slipform contractor and concrete supplier was essential. The barrier required a very stable mix to permit extrusion to the required height of 1.65m with a maximum slump of 5mm. The concrete mix design, incorporating polypropylene fibres, has taken four years to develop.
An added factor was the need to keep rail and road traffic flowing. The bulk of the concrete pours took place from 8.00pm to 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. HBS in-house traffic management team installed and maintained the traffic management on the scheme. As the project moved citybound, close to a densely populated residential area, specialist noise screens were employed for the extrusion machine to reduce noise emitted from the work area.
THE SLIPFORM PROCESS
Through value engineering, minor modifications permitted reduced foundation depths. The dedicated, highly skilled Extrudakerb team operated the slipform pavers to ensure accurate alignment and control of concrete supply. 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 of producing 18m3 per hour (25 to 30 linear meters per hour). Outputs were dependent on a number of factors including: length of barrier, quality of concrete supply and ease of access for concrete supply vehicles.
At the heart of the operation is the slipform paving machine; typically a three or four tracked prime mover to which the slipform paving mould is attached. The basic mix for barrier concrete is class C28/35 with air entrainment. Concrete design was in accordance with BS EN 206-1 and BS 8500. Aggregate selection is important and the natural interlock of a crushed angular stone is very helpful. With the sensitive nature of the concrete mix, co-ordination with delivery to site and pouring into the mould was essential. Off site trials were arranged so mix designs could be refined to suit locally available aggregates and to allow the concrete supplier to fully prepare for the project.
ACHIEVEMENTS
Waste minimisation was a principal focus as part of our Environmental Management System. To reduce the number of vehicle movements and material for disposal, substantial quantities of existing excavated granular material were recycled and reused on site. Through heavy dynamic compaction this material was capable of providing a suitable sub-grade for the barrier foundation. Other waste reduction measures included directional drilling and careful segregation of contaminated material.
The client’s acceptance of a concrete barrier solution has ensured a long life zero maintenance solution making the product sustainable to a very high degree.
The project was one of four finalists nominated for the CEF Excellence Awards in
the sub-category Infrastructure – Roads and one of four short listed for the overall award for Achieving Excellence.
For more information, contact Adrian Erwee at adrianerwee@pcoleconsult.co.uk
or James Charlesworth at james@extrudakerb.co.uk