On the face of it the two platform extensions should have been very similar – the same busy rail line out of Paddington Station with the same 125mph line speed, approximately the same length and width of extension, the platforms being extended at the same side of the station, the sites just a few miles apart and so the same trains passing through the worksite.
Even the same access point was used for some of the work. However, the solutions required from Tata Steel Projects to be able to deliver the platform extensions at West Drayton and Langley Stations required very different solutions.
The two projects formed part of the enabling works package for Crossrail West Outer Stations and followed on from the successful completion of a platform extension at Hayes & Harlington Station. Acting as principal contractor, Tata Steel Projects used its niche Modular Platform systems to be able to deliver both projects in different but equally challenging environments.
The extension at West Drayton was located on the top of a Victorian earth embankment with a raised ground profile due to a previous platform structure and with numerous buried services. Furthermore, there were residential properties immediately on the toe of the heavily vegetated embankment and so access was limited via the station access or a temporary scaffold.
It therefore became clear that a solution requiring minimal depth of construction, minimal excavation and removal of spoil and also minimal wet works was required. Fortunately, Tata Steel Projects can supply lightweight modular platform systems (previously known as the Corus Rail Modular Platform Systems) that can be constructed without the need for mechanical lifting and only requires a gang of installers.
This patented system, which is a Network Rail standard design and which has been used on over 80 new platforms and platform extension projects on the UK and European Rail networks, is unrivalled in its constructability in difficult access conditions and has enabled the delivery of projects to some extremely challenging timescales.
However, the frequent leg centres of the standard system still require a foundation and though this is typically easy to build, as the dead loads can be 60% less than equivalent concrete systems and the location of the footings can be behind the blue fencing and out of the track support zone, it still requires a simple strip footing or raft.
“At West Drayton we calculated the cubic metres of spoil removal, the amount of concrete that would have needed importing and when we also considered the narrow space between existing structures and services that was available to place the foundations we came to the conclusion that this solution was not ideal,” commented Tata Steel Projects’ Business Manager, John Wood.
Several years previously, Tata Steel Projects had developed the ‘Long Span’ platform system which had been used in parts of other schemes, and it was decided that this variant was the best option.
The ‘Long Span’ system uses the same basic premise of the standard modular platform system, as it shares many components and so has the same flexibility and future adjustability inherently designed into it, but replaces the frequent legs with a spanning ladder beam that bridges the 7.32 metre gap between pairs of piles, although other spans can be developed.
At West Drayton the construction depth available above existing critical services was constrained to such an extent that the Ladder Beam had to re-engineered.
The proximity of residents and the difficulty with spoil removal meant that Tata Steel Projects used low displacement piling for the foundations on this scheme. However; unseen obstructions in the ground caused some difficulty with this operation.
The nearest access point was also found to be unsuitable as the hardstanding was insufficient to crane ‘Long Span’ platform units onto road rail trailers. However, all twelve units of the ‘Long Span’ platform system were able to be delivered to an access point five miles from West Drayton, taken to the worksite by road rail vehicle, and the main bulk of the platform structure installed during a single shift of a weekend blockade.
Tata Steel Projects’ installers were then able to follow behind and adjust the platform system to the theoretical gauge, install rear fencing, platform lighting, signage, cess stairs and surfacing (using a thin GRP overlay system which was easy to transport to site) during traffic hours and non-disruptive possessions.
In theory, the extension at Langley Station was much simpler to construct with the possibility of creating a temporary access point adjacent to the footprint of the platform extension.
Therefore the method chosen was more typical of the Tata Steel Projects platform system. This uses a series of components that can be installed without the need for mechanical lifting. The bulk of the installation can take place behind blue safety fencing so the result is an equally rapid construction, just with a different method of working.
The foundations were also much simpler, though piling was used around the existing track drainage system. Also it was possible to deliver materials for a traditional asphalt, precast concrete coper and tactile paving surfacing.
Tata Steel Projects were also able to deliver a temporary lift to the opposite platform which was out of gauge.
Similar, yet different
So the two stations, while outwardly similar, required modular and offsite construction techniques from both ends of the spectrum, one lightweight with a high degree of repetition able to be installed manually and the other using much fewer but larger units transported and lifted into position with heavy equipment.
However, they did both have several aspects in common. The modular system allowed construction to be carried out safely by minimising hours worked on-site and to a high standard of quality by using factory quality assurance techniques for the components. The design is future-proofed by the inherent adjustability in the systems while the components are durable and meet the requirements set-out by Network Rail standards for steel platforms.
Also, the installations incorporate techniques that are inherently sustainable such as using offsite construction which minimises waste and transportation and also using steel which consists of a high degree of recycled material.
Importantly, by establishing the correct solution for the construction of each of these projects, and by working in collaboration with the client and key delivery partners, Tata Steel Projects was able to deliver both these schemes simultaneously.
There was actually one further similarity between the two projects. Both received a STAR Award from Crossrail in recognition of an excellent Health & Safety record and good site management. Teams of auditors visited both sites to conduct in depth assessments of the quality of both projects before presenting those awards. So they really were two jobs well done!