What makes HS2's bridges and viaducts different from other projects | New Civil Engineer

2022-06-15 15:07:34 By : Mr. Liu Gary

The number of different aspects that need to be considered in the design and construction of High Speed 2 (HS2)'s bridges and viaducts has not been seen on other projects, according to HS2 Ltd's head of civils structures.

HS2 Phase One will see the construction of more than 500 bridging structures, including over 50 major viaducts which will stretch for a combined total of 15km across valleys, rivers, roads and flood plains.

HS2 Ltd head of civils structures Tomas Garcia told NCE's Future of Bridges conference that there are a number of key considerations when it comes to the structures.

These include the need to minimise the whole life cost of assets and to promote offsite manufacture. In addition environmental mitigation is important, in relation to both noise and the low alignment of some viaducts, along with derailment mitigation and safety considerations. Reliability and durability is also key given the "demanding operations regime".

What makes the project different from other similar schemes, however, is the need to consider all of these aspects together.

"There are international examples that cover some of the above aspects but we couldn't find any similar projects that covered all of them," Garcia said.

As such, HS2 developed design requirements and specimen designs, prior to contract award, to help engineering firms and architects develop their designs.

"A lot of them were set up independently but we wanted to make sure all of them combined could be achieved," Garcia said.

HS2 Ltd also created a benchmark for viaducts for designers' use and the specimen designs are included in the technical standards, which are considered as part of the selection process. There are two types of specimen designs: 'beacon' structures like the Colne Valley Viaduct and a standard viaduct design, used on the Wendover Dean and Thame Valley viaducts.

Work is currently ongoing on a number of the projects impressive viaducts.

With the switching on of Dominique, the 700t bridge building machine known as a launching girder, HS2 engineers began putting in place the 1,000 unique pre-cast elements that will make up the 3.4km Colne Valley Viaduct earlier this month.

The viaduct will be the longest railway bridge in the UK. It will cross a series of lakes and waterways between Hillingdon and the M25. Construction is being led by Align JV – made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick.

The 18m-high, 18m-wide and 160m-long launching girder will sit on top of the bridge piers and lift the giant concrete deck segments that form the viaduct’s arches into position. Once a section is complete, the machine’s hydraulic rams push it forward and into position to build the next stage.

There pre-cast segments are in a variety of shapes to allow for the viaduct’s gentle curves, and each weigh up to 140t – around the size of a double-decker bus. They are being manufactured in a 105,000m3 purpose-built temporary factory close to the viaduct’s north abutment.

Meanwhile, Garcia has previously told NCE that the Thame Valley Viaduct could be a game-changer for the industry, proving that pre-fabricated structures can also be attractive.

HS2 Ltd announced that the 880m-long viaduct will be entirely pre-fabricated before being assembled on site - and Garcia believes its visual qualities show that a balance can be found between functionality and appearance.

“This viaduct potentially will change the view of the industry,” he said. “Traditionally when you talk about precast or offsite solutions, mostly people tend to think about this horrible functional solution.

“Whereas this is a very good example that something functional and engineering led can look great with the right design input. I hope this will change the view of many stakeholders.”

Crossing the flood plain of the River Thame, just outside Aylesbury, the ambitious modular design has been worked up by HS2 Ltd’s main works contractor EKFB - a team made up of Eiffage, Kier, Ferrovial Construction and Bam Nuttall - working with their design partner ASC (a joint venture between Arcadis Setec and Cowi) and architects Moxon.

Set low into the landscape with a simple and consistent profile, the underside of the viaduct will be just 3m above the ground, with 36 25m-long spans crossing the river and surrounding wetlands.

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Tagged with: Colne Valley viaduct hs2 Thame Valley Viaduct viaducts

One of the differences about HS2 bridges is that they are all paid for by the British taxpayer in their entirety, like the rest of this scandalously out-of-control project. HS2’s business plan and economics are so fundamentally flawed that it couldn’t attract private capital (the original plan). It wouldn’t get on the table of any boardroom in Britain, such are its hideous economic claims. It should have been scrapped years ago.

“…..each weigh up to 140t – around the size of a double-decker bus.” Dimensions of a double-decker bus are about 9.5m x 4.4m x 2.5m, a volume of 104.5 cu. m., which means that the density of each concrete segment is about 1.3 tonnes/cu. m., half the usual mass of reinforced concrete. Could it be the writer has got the volume units wrong, and it should be a single-decker bus?

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