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Jetties provide haul road access for the viaduct construction, keeping trucks off the road

The jetties provide construction platforms and access routes for materials and equipment.

Temporary steel jetties with a total weight of 5,000t, spanning four lakes, are playing an integral role in the construction of HS2’s Colne Valley Viaduct.

FACT FILE
HS2 Colne Valley Viaduct temporary works
Main client:
HS2
Main Works Civil Contractor: Align JV
Contractor: VolkerStevin
Structural engineer: Tony Gee & Partners
Steelwork contractor: Taziker Industrial
Steel tonnage: 5,000t

Construction of the UK’s longest railway bridge is now underway as HS2 gears up to provide a new high-speed link between London and Birmingham.

Forming an important part of the HS2 project, the 3.4km-long Colne Valley Viaduct will carry trains, travelling at speeds of over 200mph, across a series of lakes and waterways on the north-west outskirts of London.

Colne Valley covers some diverse countryside with areas of parks, green spaces and reservoirs. Along with the River Colne and the Grand Union Canal, the valley is a well-used public space offering recreational opportunities for visitors to enjoy.

In order to fit comfortably into this environment, the viaduct will be set low in the landscape, a design said to have been inspired by the flight of a stone skipping across the water. It will have a series of spans, some up to 80m-long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal.

Haul roads for the construction of the viaduct follow the bridge alignment on land, however where it spans lakes and wetlands, access is provided by temporary steel jetties that run parallel with the new structure.

Haul roads for the construction of the viaduct generally follow the bridge alignment on land, however where it spans lakes and wetlands, access is provided by temporary steel jetties that run parallel with the new structure.

The viaduct is said to have an unobtrusive design and will be set low on the landscape.

VolkerStevin is responsible for the construction of this temporary jetty on tubular piles, which will run parallel to the permanent foundations of the new viaduct. The jetty will comprise a double carriageway, two direction walkway, service passages, and storage areas with a total approximate length of 990m). Measuring 10m-wide, the four jetties are being used to help with the construction of the viaduct piers as well as providing access routes over water for plant, equipment and materials in areas that would otherwise be inaccessible.

VolkerStevin appointed Steelwork contractor Taziker Industrial, to fabricate, supply and install 5,000t of structural steelwork for the jetties. Known as jetty A, B, C and D, these not inconsiderable temporary steel structures are 384m-long, 144m-long, 300m-long and 180m-long respectively.

The jetties are being supplied to site in prefabricated steel deck modules, measuring 6m-wide x 12m-long. Using this form of offsite construction has meant a safer programme as there is less work undertaken over water, and a faster and more efficient method.

“We always have at least two modules ready to be installed at the jetty’s assembly points,” explains Taziker Managing Director Jarrod Hulme. “The modules are delivered as ladder frames, complete with crossbeams and bracings with each weighing 25t.”

“Once on site, the modules are positioned on to trestle tables before being transported to their final jetty positions.”

Positioned on a trestle, a module is made ready to be transported to its final position.

Jetty C and D were installed last year, while A and B will both complete this year (2022). The construction of each jetty followed a similar installation procedure.

The jetties were constructed sequentially with a crawler crane initially installing two x 864mm-diameter tubular steel piles, which are typically 30m-deep. A single deck module was then delivered to the rear of the crane by a Self-Propelled Modular Transporter (SPMT). It was lifted and slewed 180 degrees by the crane and placed on the piles cap heads, which connect to the module’s front.

Once the initial module was installed, every subsequent unit was lifted onto the pile caps in a similar way, while the rear of each module has a bolted connection to the previous unit.

Once a module was in place, the crane then installed a precast concrete deck unit, which was also delivered to the jetty by an SPMT in a similar manner to the module.

The installed module and deck then provided the crane with a working platform for a further two piles to be installed in readiness for the next ladder frame and deck. This procedure was repeated until the construction reached the causeway at the other side of the lake.

Taziker’s works also included the installation of safety barriers, pedestrian walkways and guardrails along the length of the jetties.

Prefabricated ladder frame modules form the jetties.

A total of 13 working platforms have also been built to enable VolkerGround Engineering to construct the cofferdams within the lakes, which in turn facilitate the construction of the viaduct’s piers. So far a total of 35 out of 56 cofferdams have been installed by the VolkerGround Engineering team, including 3 in the lakes.

These working platforms, constructed in pairs and formed with slightly larger modules, measuring 14m x 9m, are connected to the jetty at approximately 50m intervals.

Taziker worked collaboratively with VolkerStevin to agree the working procedure and design of the jetties with statutory bodies including the Environment Agency, to ensure the integrity of water and wildlife. The decking of the jetties has sealed joints and a cross-fall to a drainage system designed to minimise the risk of contaminating the lakes.

Mr Hulme says: “Once complete the Colne Valley Viaduct will be a spectacular and essential part of HS2 Phase one. By supplying and installing a major temporary component that is meeting the requirement from the Main Works Civils Contractor Align JV to keep construction traffic off local roads, Taziker has shown the quality and innovation we can deliver on major projects.”

One of the final modules is lifted into place to complete a jetty.

Summing up, VolkerStevin Senior Project Manager, Andy Dyer says: “Working closely with Taziker we are making good progress on site. Taziker’s input into the design aspect of the project has created a value engineered scheme, assisting in producing a cost efficient and practical solution.”

Once the Colne Valley Viaduct is completed in 2023, all of the temporary jetties will be disassembled and removed from their respective sites.

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