Britpave: The British In-Situ Concrete Paving Association

High speed link must be built right first time

The proposed 100 mile HS2 rail line will see trains travelling at speeds of up to 250mph and will reduce the journey time between London and Birmingham from 1 hour and 24 minutes to 49 minutes. Construction of the line is due to start in 2016 with completion in 2026 following which a second Y-shaped route will take the line north to Manchester and Yorkshire. The high speed route is an infrastructure improvement that is sorely needed. However, if HS2 is to really to fulfil its potential then it must be built right first time.

The UK’s rail network compares poorly with many other countries. It is based upon the 19th century ballast track system that is unsuited to the performance demands and sustainability criteria of the 21st century.

One of the major problems with ballast track is that moves under load which results in the need for on-going maintenance to restore the line and level and for the ballast to be regularly cleaned or replaced. The speed of high speed trains travelling between 300kph to 400kph results in powerful air flows which can cause the ballast to fly and damage the undercarriage of the train. Furthermore, there is the potential issue of ballast settlement. In France, where they opted for traditional ballast when the high-speed TGV network was developed, they have managed to make it work – but at a cost. On some lines the rails have to be swept clean and the ballast replaced and repacked every night. The French are now reported to be examining replacing ballast with concrete slab track having found that the use of ballast tracks undermines the speed, efficiency and safety of high speed trains.

“For the UK a range of solutions are being examined”, explained Joe Quirke, Chairman of the Britpave Rail task Group. “These include limiting the speed of trains, gluing the ballast or using a surface net to contain the ballast. The simplest solution is don’t use ballast.”

Quirke advocates the use of modern concrete slab track. Concrete slab track construction has integral design that optimises the design of trackside elements and it maximises operating efficiency by eliminating unplanned maintenance, provides high levels of safety and comfort and impressive long-term performance. In addition, slab track allows reduced construction depth and structure gauge. All of these benefits add-up to a lower whole life cost compared with ballasted track that easily offset any higher initial capital cost of the track system.

“Concrete slab track is used used by the highly successful Japanese rail network and increasingly throughout mainland Europe”, explained Quirke. “It is competitive on first cost and cheaper on whole life cost when compared to the equivalent ballasted system, offers superior performance in terms of reliability and track quality and has a low maintenance, long-term operational life.”

Concrete slab track for tunnels has been used in the UK for rail tunnels for reduced maintenance and reduced height. This is an important consideration for HS2 where extensive tunnelling is proposed to reduce its environmental impact. Unfortunately, outside of the tunnel ballast track is used.

This results in the problem of transition joints between ballast and slab track which can impair the ride quality. If the joints are spread over 50m the ride quality should not be affected. However, this assumes ‘very good’ ballast track throughout the transition and this is just about impossible to ensure and maintain. “Again there is a simple solution, avoid transitions joints by using slabtrack throughout”, said Quirke.

“High-speed rail should be fast, reliable, low-carbon mode of transport with low maintenance and high long-term performance. That will only be achieved if HS2 is built right first time”, said Quirke.